Ultrafast Magnetic Processes Observed 'Live' Using an X-Ray Laser

Detail of the structure of cupric oxide (CuO). The copper atoms (green) carry a magnetic moment, behaving like small compass needles. The direction of the magnetic moment is illustrated by a red arrow. A point means that the arrow is pointing out of the surface (we are looking at its sharp end), a cross shows that the arrow is pointing into the surface (we are looking at its tail end). The magnetic structure changes significantly as the temperature increases above 213 Kelvin (around -60°C). One aspect of this change is a difference in the period of the magnetic order. Unlike the ordering at low temperatures, the magnetic structure in the temperature range 213 K to 230 K is incommensurate: its period does not ‘fit’ with the period of the crystal structure of copper and oxygen atoms. To be precise, a full rotation of the direction of the magnetic moment does not require exactly four atomic separations, but a little more or a little less, depending on the direction. (Credit: Image courtesy of Paul Scherrer Institut (PSI))

ScienceDaily (Jan. 23, 2012) — In first-of-their-kind experiments performed at the American X-ray laser LCLS, a collaboration led by researchers from the Paul Scherrer Institute has been able to precisely follow how the magnetic structure of a material changes.

This is another milestone, because such investigations will also be a major focus of research at the planned Swiss X-ray Laser, Swiss FEL, at PSI. The results could contribute to the development of new technologies for magnetic storage media for the future.The study was carried out on cupric oxide (CuO). The change of structure was initiated by a laser pulse, and then, with the help of short X-ray pulses, near-instantaneous images were obtained at different points in time for individual intermediate steps during the process. It appears as if the structure begins to change 400 femtoseconds after the laser pulse strikes (1 femtosecond = 0.000 000 000 000 001 seconds). Apparently, the fundamental magnets within the material need that much time to communicate with each other and then react. In addition to this scientific result, the work proves that it is actually possible with X-ray lasers to follow certain types of extremely rapid magnetic processes.

The researchers have reported on their work in the latest edition of the technical journal Physical Review Letters (PRL).

Materials with particular magnetic properties are the basis of many current technologies, in particular, data storage on hard discs and in other media. For this, the magnetic orientation in the material is most often used: the atoms in the material behave to some extent like tiny rod magnets ("spins"). These mini-magnets can be oriented in different ways and information can be stored through their orientation. For efficient data storage, it is crucial that old data can be rapidly overwritten. This is possible if the magnetic orientation in a material can be altered in a very short time. To develop innovative materials which can store data quickly, it is therefore important to understand exactly how this change occurs as a function of time.

Magnetic orientation in motion

In experiments performed at the X-ray laser LCLS at Stanford, California, a collaboration led by researchers from the Paul Scherrer Institute have been able to study the magnetic orientation in cupric oxide, CuO. This material demonstrates completely different magnetic orientations depending on temperature: Below -60°C, the spins, which function in the copper atoms (Cu) like magnets, point periodically in one direction and then the opposite; between -60°C and -43°C, they are arranged helically, as if they were forming a spiral staircase. Although the spin orientations for the two arrangements have been known for some time, the time required to move from one arrangement to the other has only now been shown by the experiment.

"In our investigation, we began with a 'cold' sample and then heated it with an intense flash of light from an optical laser," explains Steven Johnson, spokesman for the PSI experiment. "Shortly after this, we determined the structure of the sample by illuminating it with an extremely short pulse from an X-ray laser. When we repeated this at different time intervals between the flash of light and the X-ray pulse, we were able to reconstruct the course of the change in the magnetic structure."

Mini-magnets need 400 femtoseconds to agree amongst themselves.

The results show that it takes about 400 femtoseconds before the magnetic structure begins to alter visibly. Then the structure gradually reaches its final state. The more intense the initiating flash of light, the faster the change of state. "The spins of all copper atoms are involved in the magnetic structure. Thus the atoms at opposite ends of the material must be coordinated before the structure can change. This takes 400 femtoseconds," explains Urs Staub, one of the PSI researchers responsible. "For cupric oxide, that is the fundamental limit; it simply cannot happen faster than that. This depends upon how strongly the spins are coupled between neighbouring atoms."

There is a good reason why the researchers were particularly interested in cupric oxide. Along with the screw-like magnetic orientation that occurs between -60°C and -43°C, the material is also 'multiferroic', a material where electrical and magnetic processes mutually influence one another. These materials have many different potential areas of application where magnetism and electronics interact.

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The above story is reprinted from materials provided byPaul Scherrer Institut (PSI), via AlphaGalileo.

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---

Journal Reference:

1. S. Johnson, R. de Souza, U. Staub, P. Beaud, E. Möhr-Vorobeva, G. Ingold, A. Caviezel, V. Scagnoli, W. Schlotter, J. Turner, O. Krupin, W.-S. Lee, Y.-D. Chuang, L. Patthey, R. Moore, D. Lu, M. Yi, P. Kirchmann, M. Trigo, P. Denes, D. Doering, Z. Hussain, Z.-X. Shen, D. Prabhakaran, A. Boothroyd. Femtosecond Dynamics of the Collinear-to-Spiral Antiferromagnetic Phase Transition in CuO.Physical Review Letters, 2012; 108 (3) DOI:10.1103/PhysRevLett.108.037203

2-D electron liquid solidifies in a magnetic field

ScienceDaily (Nov. 5, 2011) — Physicists from the Georgia Institute of Technology have developed a theory that describes, in a unified manner, the coexistence of liquid and pinned solid phases of electrons in two dimensions under the influence of a magnetic field. The theory also describes the transition between these phases as the field is varied. The theoretical predictions by Constantine Yannouleas and Uzi Landman, from Georgia Tech's School of Physics, aim to explain and provide insights into the origins of experimental findings published last year by a team of researchers from Princeton, Florida State and Purdue universities.

The research appears in the Oct. 27 edition of the journal Physical Review B.

The experimental discovery in 1982 of a new Hall conductance step at a fraction ?=1/m with m=3, that is at (1/3)e2/h (with more conductance steps, at other m, found later) -- where h is the Planck constant and e is the electron charge -- was made for two-dimensional electrons at low temperatures and strong magnetic fields and was greeted with great surprise. The theoretical explanation of this finding a year later by Robert Laughlin in terms of a new form of a quantum fluid, earned him and the experimentalists Horst Störmer and Daniel Tsui the 1998 Nobel Prize with the citation "for the discovery of a new form of quantum fluid with fractionally charged excitations." These discoveries represent conceptual breakthroughs in the understanding of matter, and the fractional quantum Hall effect (FQHE) liquid states, originating from the highly correlated nature of the electrons in these systems, have been termed as new states of matter.

"The quantum fluid state at the 1/3 primary fraction is the hallmark of the FQHE, whose theoretical understanding has been formulated around the antithesis between a new form of quantum fluid and the pinned Wigner crystal," said Landman, Regents' and Institute Professor in the School of Physics, F.E. Callaway Chair and director of the Center for Computational Materials Science (CCMS) at Georgia Tech. "Therefore, the discovery of pinned crystalline signatures in the neighborhood of the 1/3 FQHE fraction, measured as resonances in the microwave spectrum of the two-dimensional electron gas and reported in the Physical Review Letters in September 2010 by a group of researchers headed by Daniel Tsui, was rather surprising," he added.

Indeed, formation of a hexagonally ordered two-dimensional electron solid phase, a so called Wigner crystal (WC) named after the Nobel laureate physicist Eugene Wigner who predicted its existence in 1934, has been anticipated for smaller quantum Hall fractional fillings, ?, of the lowest Landau level populated by the electrons at high magnetic fields, for example ? = 1/9, 1/7 and even 1/5. However, the electrons in the ?=1/3 fraction were believed to resist crystallization and remain liquid.

The Georgia Tech physicists developed a theoretical formalism that, in conjunction with exact numerical solutions, provides a unified microscopic approach to the interplay between FQHE liquid and Wigner solid states in the neighborhood of the 1/3 fractional filling. A major advantage of their approach is the use of a single class of variational wave functions for description of both the quantum liquid and solid phases.

"Liquid characteristics of the fractional quantum Hall effect states are associated with symmetry-conserving vibrations and rotations of the strongly interacting electrons and they coexist with intrinsic correlations that are crystalline in nature," Senior Research Scientist Yannouleas and Landman wrote in the opening section of their paper. "While the electron densities of the fractional quantum Hall effect liquid state do not exhibit crystalline patterns, the intrinsic crystalline correlations which they possess are reflected in the emergence of a sequence of liquid states of enhanced stability, called cusp states, that correspond in the thermodynamic limit to the fractional quantum Hall effect filling fractions observed in Hall conductance measurements," they added.

The key to their explanation of the recent experimental observations pertaining to the appearance of solid characteristics for magnetic fields in the neighborhood of the 1/3 filling fraction is their finding that "away from the exact fractional fillings, for example near ?=1/3, weak pinning perturbations, due to weak disorder, may overcome the energy gaps between adjacent good angular momentum symmetry-conserving states. The coupling between these states generates broken-symmetry ground states whose densities exhibit spatial crystalline patterns. At the same time, however, the energy gap between the ground state at ?=1/3 and adjacent states is found to be sufficiently large to prevent disorder-induced mixing, thus preserving its quantum fluid nature."

Furthermore, the work shows that the emergence of the crystalline features, via the pinning perturbations, is a consequence of the aforementioned presence of crystalline correlations in the symmetry-conserving states. Consequently, mixing rules that govern the nature of the disorder-pinned crystalline states have been formulated and tested. Extrapolation of the calculated results to the thermodynamic limit shows development of a hexagonal Wigner crystal with enhanced stability due to quantum correlations.

"In closing, the nature of electrons in the fractional quantum Hall regime continues now for close to three decades to be a subject of great fascination, a research field that raises questions whose investigations can lead to deeper conceptual understanding of matter and many-body phenomena, and a rich source of surprise and discovery," said Landman.

This work was supported by the Office of Basic Energy Sciences of the US Department of Energy.

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Journal Reference:

Constantine Yannouleas, Uzi Landman. Unified microscopic approach to the interplay of pinned-Wigner-solid and liquid behavior of the lowest Landau-level states in the neighborhood of ?=1/3. Physical Review B, 2011; 84 (16) DOI: 10.1103/PhysRevB.84.165327

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'Magnetic tongue' ready to help produce tastier processed foods

ScienceDaily (Oct. 26, 2011) — The "electronic nose," which detects odors, has a companion among emerging futuristic "e-sensing" devices intended to replace abilities that once were strictly human-and-animal-only. It is a "magnetic tongue" -- a method used to "taste" food and identify ingredients that people describe as sweet, bitter, sour, etc. A report on use of the method to taste canned tomatoes appears in ACS' Journal of Agricultural and Food Chemistry.

Antonio Randazzo, Anders Malmendal, Ettore Novellino and colleagues explain that sensing the odor and flavor of food is a very complex process. It depends not only on the combination of ingredients in the food, but also on the taster's emotional state. Trained taste testers eliminate some of the variation, but food processors need more objective ways to measure the sensory descriptor of their products. That's where electronic sensing technologies, like E-noses, come into play.

However, current instruments can only analyze certain food components and require very specific sample preparation. To overcome these shortcomings, Randazzo and Malmendal's team turned to nuclear magnetic resonance spectroscopy (NMR) to test its abilities as "a magnetic tongue."

The researchers analyzed 18 canned tomato products from various markets with NMR and found that the instrument could estimate most of the tastes assessed by the human taste testers. But the NMR instrument went even farther. By determining the chemical composition, it showed which compound is related to which sensory descriptor. The researchers say that the "magnetic tongue" has good potential as a rapid, sensitive and relatively inexpensive approach for food processing companies to use.

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Journal Reference:

Anders Malmendal, Claudia Amoresano, Roberta Trotta, Ilaria Lauri, Stefano De Tito, Ettore Novellino, Antonio Randazzo. NMR Spectrometers as “Magnetic Tongues”: Prediction of Sensory Descriptors in Canned Tomatoes. Journal of Agricultural and Food Chemistry, 2011; 59 (20): 10831 DOI: 10.1021/jf203803q

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Magnetic attraction: Microchip demonstrates concept of 'MRAM for biomolecules'

ScienceDaily (Oct. 19, 2011) — Researchers from the National Institute of Standards and Technology (NIST) and University of Colorado Boulder (CU) have developed a low-power microchip that uses a combination of microfluidics and magnetic switches to trap and transport magnetic beads. The novel transport chip may have applications in biotechnology and medical diagnostics.

A key innovation in the new chip is the use of magnetic switches like those in a computer random access memory. As described in a new paper, the NIST/CU team used the chip to trap, release and transport magnetic beads that potentially could be used as transport vehicles for biomolecules such as DNA.

Conventional microfluidics systems use pumps and valves to move particles and liquids through channels. Magnetic particle transport microchips offer a new approach to microfluidics but generally require continuous power and in some cases cooling to avoid sample damage from excessive heating. The NIST/CU technology eliminates these drawbacks while offering the possibility for random access two-dimensional control and a memory that lasts even with the power off.

The demo chip features two adjacent lines of 12 thin-film magnet switches called spin valves, commonly used as magnetic sensors in read heads of high-density computer disk drives. In this case, however, the spin valves have been optimized for magnetic trapping. Pulses of electric current are used to switch individual spin valve magnets "on" to trap a bead, or "off" to release it, and thereby move the bead down a ladder formed by the two lines (see video clip at: http://www.nist.gov/pml/electromagnetics/magnetics/magnetic-101311.cfm). The beads start out suspended in salt water above the valves before being trapped in the array.

"It's a whole new way of thinking about microfluidics," says NIST physicist John Moreland. "The cool thing is it's a switchable permanent magnet -- after it's turned on it requires no power. You beat heat by switching things quickly, so you only need power for less than a microsecond."

NIST researchers previously demonstrated that spin valves could be used to trap and rotate particles and recently were awarded two patents related to the idea of a magnetic chip.

Magnetic tags are used in bioassays such as protein and DNA purification and cell breakdown and separation. The chip demonstration provides a conceptual foundation for a more complex magnetic random access memory (MRAM) for molecular and cellular manipulation. For example, programmable microfluidic MRAM chips might simultaneously control a large number of beads, and the attached molecules or cells, to assemble "smart" tags with specified properties, such as an affinity for a given protein at a specific position in the array. NIST is also interested in developing cellular and molecular tags for magnetic resonance imaging (MRI) studies in which individual cells, such as cancer cells or stem cells, would be tagged with a smart magnetic biomarker that can be tracked remotely in an MRI scanner, Moreland says. Automated spin valve chips might also be used in portable instruments for rapid medical diagnosis or DNA sequencing.

The lead author of the new paper, Wendy Altman, did the research at NIST as a CU graduate student working on her doctoral thesis. Another author, Bruce Han, was a CU student in NIST's Summer Undergraduate Research Fellowship (SURF) program.

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Journal Reference:

Wendy R. Altman, John Moreland, Stephen E. Russek, Bruce W. Han, Victor M. Bright. Controlled transport of superparamagnetic beads with spin-valves. Applied Physics Letters, 2011; 99 (14): 143703 DOI: 10.1063/1.3645615

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New nanostructure-based process will streamline production of magnetic materials

ScienceDaily (Sep. 27, 2011) — Scientists at the University of Massachusetts Amherst report that for the first time they have designed a much simpler method of preparing ordered magnetic materials than ever before, by coupling magnetic properties to nanostructure formation at low temperatures.

The innovative process allows them to create room-temperature ferromagnetic materials that are stable for long periods more effectively and with fewer steps than more complicated existing methods. The approach is outlined by UMass Amherst polymer scientist Gregory Tew and colleagues in the Sept. 27 issue of Nature Communications.

Tew explains that his group's signature improvement is a one-step method to generate ordered magnetic materials based on cobalt nanostructures by encoding a block copolymer with the appropriate chemical information to self-organize into nanoscopic domains. Block copolymers are made up of two or more single-polymer subunits linked by covalent chemical bonds.

The new process delivers magnetic properties to materials upon heating the sample once to a relatively low temperature, about 390 degrees (200 degrees Celsius), which transforms them into room-temperature, fully magnetic materials. Most previous processes required either much higher temperatures or more process steps to achieve the same result, which increases costs, Tew says.

He adds, "The small cobalt particles should not be magnetic at room temperature because they are too small. However, the block copolymer's nanostructure confines them locally which apparently induces stronger magnetic interactions among the particles, yielding room-temperature ferromagnetic materials that have many practical applications."

"Until now, it has not been possible to produce ordered, magnetic materials via block copolymers in a simple process," Tew says. "Current methods require multiple steps just to generate the ordered magnetic materials. They also have limited effectiveness because they may not retain the fidelity of the ordered block copolymer, they can't confine the magnetic materials to one domain of the block copolymer, or they just don't produce strongly magnetic materials. Our process answers all these limitations."

Magnetic materials are used in everything from memory storage devices in our phones and computers to the data strips on debit and credit cards. Tew and colleagues have discovered a way to build block copolymers with the necessary chemical information to self-organize into nanoscopic structures one millionth of a millimeter thin, or about 50,000 times thinner than the average human hair.

Earlier studies have demonstrated that block copolymers can be organized over relatively large areas. What makes the UMass Amherst research group's results so intriguing, Tew says, is the possible coupling of long-range organization with improved magnetic properties. This could translate into lower-cost development of new memory media, giant magneto-resistive devices and futuristic spintronic devices that might include "instant on" computers or computers that require much less power, he points out.

He adds, "Although work remains to be done before new data storage applications are enabled, for example making the magnets harder, our process is highly tunable and therefore amendable to incorporating different types of metal precursors. This result should be interesting to every scientist in nanotechnology because it shows conclusively that nano-confinement leds to completely new properties, in this case room temperature magnetic materials."

"Our work highlights the importance of learning how to control a material's nanostructure. We show that the nanostructure is directly related to an important and practical outcome, that is, the ability to generate room-temperature magnets."

"Our work highlights the importance of learning how to control a material's nanostructure. We show that the nanostructure is directly related to an important and practical outcome, that is, the ability to generate room temperature magnets." As part of this study, the UMass Amherst team also demonstrated that using a block copolymer or nanoscopic material results in a material that is magnetic at room temperature. By contrast, using a homopolymer, or unstructured material, leads only to far less useful non- or partial-magnetic materials.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Massachusetts at Amherst.

Journal Reference:

Zoha M. AL-Badri, Raghavendra R. Maddikeri, Yongping Zha, Hitesh D. Thaker, Priyanka Dobriyal, Raja Shunmugam, Thomas P. Russell, Gregory N. Tew. Room temperature magnetic materials from nanostructured diblock copolymers. Nature Communications, 2011; 2: 482 DOI: 10.1038/ncomms1485

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Cloaking magnetic fields: First antimagnet developed

ScienceDaily (Sep. 23, 2011) — Spanish researchers have designed what they believe to be a new type of magnetic cloak, which shields objects from external magnetic fields, while at the same time preventing any magnetic internal fields from leaking outside, making the cloak undetectable.

The development of such a device, described as an 'antimagnet', could offer many beneficial applications, such as protecting a ship's hull from mines designed to detonate when a magnetic field is detected, or allowing patients with pacemakers or cochlear implants to use medical equipment.

In their study, published Sept. 23, in the Institute of Physics and German Physical Society's New Journal of Physics, researchers have proved that such a cloak could be built using practical and available materials and technologies, and used to develop an array of applications.

Take, for example, a patient with a pacemaker undergoing an MRI scan. If an MRI's large magnetic field interacts with the pacemaker, it can cause serious damage to both the device and the patient. The metal in the pacemaker could also interact with and distort the MRI's large magnetic field, affecting the machine's detection capabilities.

The researchers, from Universitat Autònoma de Barcelona, are aware that the technology could also be used by criminals to dodge security systems, for example in airports and shops, but they are confident that the new research could benefit society in a positive way, while the risks could be minimized by informing security officials about potential devices, enabling them to anticipate and neutralize problems.

Lead author, Professor Alvar Sanchez, said, "The ideas of this device and their potential applications are far-reaching; however it is conceivable that they could be used for reducing the magnetic signature of forbidden objects, with the consequent threat to security. For these reasons, this research could be taken into account by security officials in order to design safer detection systems and protocols."

The antimagnet has been designed to consist of several layers. The inner layer would consist of a superconducting material that would function to stop a magnetic field from leaking outside of the cloak, which would be very useful to cloak certain metals.

A downside to using this material, however, is that it would distort an external magnetic field placed over the cloak, making it detectable, so the device would need to be combined with several outer layers of metamaterials, which have varying levels of magnetic field permeability, to correct this distortion and leave the magnetic field undisturbed.

The researchers demonstrated the feasibility of the cloak using computer simulations of a ten-layered cylindrical device cloaking a single small magnet.

Impressively, the researchers also showed that the cloak could take on other shapes and function when the cylinder was not fully enclosed, meaning that applications for pacemakers and cochlear implants are even more feasible, given that they require wires to connect to other parts of the body.

"We indeed believe, and hope, that some laboratories could start constructing an antimagnet soon. Of the two components, superconductors are readily available, for example in cylindrical shape, and the key point would be to make the magnetic layers with the desired properties. This may take a bit of work but in principle the ingredients are there," continued Professor Sanchez.

An Institute of Physics spokesperson said, "The research group have put forward a novel and, most importantly, conceivable plan for a magnetic cloak. The obvious next step will be to translate design into fabrication so some of the wide-ranging applications can be realised."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

Alvaro Sanchez, Carles Navau, Jordi Prat-Camps, Du-Xing Chen. Antimagnets: controlling magnetic fields with superconductor–metamaterial hybrids. New Journal of Physics, 2011; 13 (9): 093034 DOI: 10.1088/1367-2630/13/9/093034

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New nanostructure-based process will streamline production of magnetic materials

ScienceDaily (Sep. 27, 2011) — Scientists at the University of Massachusetts Amherst report that for the first time they have designed a much simpler method of preparing ordered magnetic materials than ever before, by coupling magnetic properties to nanostructure formation at low temperatures.

The innovative process allows them to create room-temperature ferromagnetic materials that are stable for long periods more effectively and with fewer steps than more complicated existing methods. The approach is outlined by UMass Amherst polymer scientist Gregory Tew and colleagues in the Sept. 27 issue of Nature Communications.

Tew explains that his group's signature improvement is a one-step method to generate ordered magnetic materials based on cobalt nanostructures by encoding a block copolymer with the appropriate chemical information to self-organize into nanoscopic domains. Block copolymers are made up of two or more single-polymer subunits linked by covalent chemical bonds.

The new process delivers magnetic properties to materials upon heating the sample once to a relatively low temperature, about 390 degrees (200 degrees Celsius), which transforms them into room-temperature, fully magnetic materials. Most previous processes required either much higher temperatures or more process steps to achieve the same result, which increases costs, Tew says.

He adds, "The small cobalt particles should not be magnetic at room temperature because they are too small. However, the block copolymer's nanostructure confines them locally which apparently induces stronger magnetic interactions among the particles, yielding room-temperature ferromagnetic materials that have many practical applications."

"Until now, it has not been possible to produce ordered, magnetic materials via block copolymers in a simple process," Tew says. "Current methods require multiple steps just to generate the ordered magnetic materials. They also have limited effectiveness because they may not retain the fidelity of the ordered block copolymer, they can't confine the magnetic materials to one domain of the block copolymer, or they just don't produce strongly magnetic materials. Our process answers all these limitations."

Magnetic materials are used in everything from memory storage devices in our phones and computers to the data strips on debit and credit cards. Tew and colleagues have discovered a way to build block copolymers with the necessary chemical information to self-organize into nanoscopic structures one millionth of a millimeter thin, or about 50,000 times thinner than the average human hair.

Earlier studies have demonstrated that block copolymers can be organized over relatively large areas. What makes the UMass Amherst research group's results so intriguing, Tew says, is the possible coupling of long-range organization with improved magnetic properties. This could translate into lower-cost development of new memory media, giant magneto-resistive devices and futuristic spintronic devices that might include "instant on" computers or computers that require much less power, he points out.

He adds, "Although work remains to be done before new data storage applications are enabled, for example making the magnets harder, our process is highly tunable and therefore amendable to incorporating different types of metal precursors. This result should be interesting to every scientist in nanotechnology because it shows conclusively that nano-confinement leds to completely new properties, in this case room temperature magnetic materials."

"Our work highlights the importance of learning how to control a material's nanostructure. We show that the nanostructure is directly related to an important and practical outcome, that is, the ability to generate room-temperature magnets."

"Our work highlights the importance of learning how to control a material's nanostructure. We show that the nanostructure is directly related to an important and practical outcome, that is, the ability to generate room temperature magnets." As part of this study, the UMass Amherst team also demonstrated that using a block copolymer or nanoscopic material results in a material that is magnetic at room temperature. By contrast, using a homopolymer, or unstructured material, leads only to far less useful non- or partial-magnetic materials.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Massachusetts at Amherst.

Journal Reference:

Zoha M. AL-Badri, Raghavendra R. Maddikeri, Yongping Zha, Hitesh D. Thaker, Priyanka Dobriyal, Raja Shunmugam, Thomas P. Russell, Gregory N. Tew. Room temperature magnetic materials from nanostructured diblock copolymers. Nature Communications, 2011; 2: 482 DOI: 10.1038/ncomms1485

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Cloaking magnetic fields: First antimagnet developed

ScienceDaily (Sep. 23, 2011) — Spanish researchers have designed what they believe to be a new type of magnetic cloak, which shields objects from external magnetic fields, while at the same time preventing any magnetic internal fields from leaking outside, making the cloak undetectable.

The development of such a device, described as an 'antimagnet', could offer many beneficial applications, such as protecting a ship's hull from mines designed to detonate when a magnetic field is detected, or allowing patients with pacemakers or cochlear implants to use medical equipment.

In their study, published Sept. 23, in the Institute of Physics and German Physical Society's New Journal of Physics, researchers have proved that such a cloak could be built using practical and available materials and technologies, and used to develop an array of applications.

Take, for example, a patient with a pacemaker undergoing an MRI scan. If an MRI's large magnetic field interacts with the pacemaker, it can cause serious damage to both the device and the patient. The metal in the pacemaker could also interact with and distort the MRI's large magnetic field, affecting the machine's detection capabilities.

The researchers, from Universitat Autònoma de Barcelona, are aware that the technology could also be used by criminals to dodge security systems, for example in airports and shops, but they are confident that the new research could benefit society in a positive way, while the risks could be minimized by informing security officials about potential devices, enabling them to anticipate and neutralize problems.

Lead author, Professor Alvar Sanchez, said, "The ideas of this device and their potential applications are far-reaching; however it is conceivable that they could be used for reducing the magnetic signature of forbidden objects, with the consequent threat to security. For these reasons, this research could be taken into account by security officials in order to design safer detection systems and protocols."

The antimagnet has been designed to consist of several layers. The inner layer would consist of a superconducting material that would function to stop a magnetic field from leaking outside of the cloak, which would be very useful to cloak certain metals.

A downside to using this material, however, is that it would distort an external magnetic field placed over the cloak, making it detectable, so the device would need to be combined with several outer layers of metamaterials, which have varying levels of magnetic field permeability, to correct this distortion and leave the magnetic field undisturbed.

The researchers demonstrated the feasibility of the cloak using computer simulations of a ten-layered cylindrical device cloaking a single small magnet.

Impressively, the researchers also showed that the cloak could take on other shapes and function when the cylinder was not fully enclosed, meaning that applications for pacemakers and cochlear implants are even more feasible, given that they require wires to connect to other parts of the body.

"We indeed believe, and hope, that some laboratories could start constructing an antimagnet soon. Of the two components, superconductors are readily available, for example in cylindrical shape, and the key point would be to make the magnetic layers with the desired properties. This may take a bit of work but in principle the ingredients are there," continued Professor Sanchez.

An Institute of Physics spokesperson said, "The research group have put forward a novel and, most importantly, conceivable plan for a magnetic cloak. The obvious next step will be to translate design into fabrication so some of the wide-ranging applications can be realised."

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and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

Alvaro Sanchez, Carles Navau, Jordi Prat-Camps, Du-Xing Chen. Antimagnets: controlling magnetic fields with superconductor–metamaterial hybrids. New Journal of Physics, 2011; 13 (9): 093034 DOI: 10.1088/1367-2630/13/9/093034

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Scientists prove existence of 'magnetic ropes' that cause solar storms

ScienceDaily (June 16, 2011) — George Mason University scientists discovered recently that a phenomenon called a giant magnetic rope is the cause of solar storms. Confirming the existence of this formation is a key first step in helping to mitigate the adverse effects that solar storm eruptions can have on satellite communications on Earth.

The discovery was made by associate professor Jie Zhang and his graduate student Xin Cheng using images from the NASA Solar Dynamic Observatory (SDO) spacecraft.

Though the magnetic rope was believed to be the cause of these giant eruptions on the Sun, scientists had previously not been able to prove this phenomenon existed because of how quickly the rope moves.

However, through close examination of images taken by the Atmospheric Imaging Assembly (AIA) telescope on board the SDO, Zhang was able to pinpoint an area of the sun where a magnetic rope was forming. The AIA telescope suite is able to capture images of the Sun every 10 seconds, 24 hours a day. This unprecedented cadence in time helped the discovery.

"The magnetic rope triggers a solar eruption. Scientists have been debating whether or not this magnetic rope exists before a solar eruption. I believe that the result of this excellent observation helps finally solve this controversial issue," says Zhang.

A solar storm is a violent eruption from the Sun, sending billions of tons of charged material, also called plasma, into space at a speed of more than one million miles per hour. The cloud of plasma carries with it a strong magnetic field. When the magnetized cloud reaches Earth one to three days later, a huge amount of energy is deposited into the magnetosphere of Earth.

Normally Earth's magnetosphere shields this harmful solar wind and protects the environment. However, a solar storm has the potential to disrupt the shielding effect and produce severe space weather, which can have harmful effects on a wide array of technological systems, including satellite operation, communication and navigation and electric power grids.

Zhang's research will help in giving early warning about solar storms and help to minimize the damage done by space weather here on Earth.

"Understanding the eruption process of these storms will definitely help us better predict them," says Zhang. "We cannot prevent solar storms, just like we cannot prevent earthquakes or volcanoes. But the development of prediction capacity can help mitigate adverse effects. For instance, satellite operators can power-down key systems to prevent the possible damage to the systems."

It is widely believed that magnetic fields in the Sun play an essential role in storing energy and powering solar storms. However, the exact form that magnetic field lines take prior to the eruption are highly controversial. Most field lines are semi-circular loops with their foot-points rooted on the surface of the Sun. They cannot erupt easily, and in fact, they often play the role of preventing the eruption.

Scientists suspected that the magnetic rope, if it indeed existed, was the phenomenon that powered the eruption. A magnetic rope contains many magnetic field lines wrapping around a center axis and possibly twisting around each other. Because of the twisting, a strong electric current can be carried by the magnetic rope. Theoretically, the electric current could produce a sufficient electro-magnetic force to overcome the overlying constraining force from other field lines and power the magnetic rope to move outward.

AIA images now reveal that, before an eruption, there is a long and low-lying channel running through the entire active region, which heats to a temperature as high as 10 million degrees, and slowly rises. When it reaches a critical point, it starts to erupt quickly. It is a feature distinctly different from the surrounding magnetic field lines. This particular hot channel is now believed to be the magnetic rope that scientists have been looking for.

Zhang is an associate professor in the School of Physics, Astronomy and Computational Sciences and works with the Space Weather Lab at George Mason University. His results were reported at the American Astronomical Society Solar Physics Division Meeting, held in Las Cruces, New Mexico on June 12-16, 2011.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by George Mason University.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Using magnets to help prevent heart attacks: Magnetic field can reduce blood viscosity, physicist discovers

ScienceDaily (June 8, 2011) — If a person's blood becomes too thick it can damage blood vessels and increase the risk of heart attacks. But a Temple University physicist has discovered that he can thin the human blood by subjecting it to a magnetic field.

Rongjia Tao, professor and chair of physics at Temple University, has pioneered the use of electric or magnetic fields to decrease the viscosity of oil in engines and pipelines. Now, he is using the same magnetic fields to thin human blood in the circulation system.

Because red blood cells contain iron, Tao has been able to reduce a person's blood viscosity by 20-30 percent by subjecting it to a magnetic field of 1.3 Telsa (about the same as an MRI) for about one minute.

Tao and his collaborator tested numerous blood samples in a Temple lab and found that the magnetic field polarizes the red blood cells causing them to link together in short chains, streamlining the movement of the blood. Because these chains are larger than the single blood cells, they flow down the center, reducing the friction against the walls of the blood vessels. The combined effects reduce the viscosity of the blood, helping it to flow more freely.

When the magnetic field was taken away, the blood's original viscosity state slowly returned, but over a period of several hours.

"By selecting a suitable magnetic field strength and pulse duration, we will be able to control the size of the aggregated red-cell chains, hence to control the blood's viscosity," said Tao. "This method of magneto-rheology provides an effective way to control the blood viscosity within a selected range."

Currently, the only method for thinning blood is through drugs such as aspirin; however, these drugs often produce unwanted side effects. Tao said that the magnetic field method is not only safer, it is repeatable. The magnetic fields may be reapplied and the viscosity reduced again. He also added that the viscosity reduction does not affect the red blood cells' normal function.

Tao said that further studies are needed and that he hopes to ultimately develop this technology into an acceptable therapy to prevent heart disease.

Tao and his former graduate student, Ke "Colin" Huang, now a medical physics resident in the Department of Radiation Oncology at the University of Michigan, are publishing their findings in the journal Physical Review E.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Temple University, via EurekAlert!, a service of AAAS.

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Scientists prove existence of 'magnetic ropes' that cause solar storms

ScienceDaily (June 16, 2011) — George Mason University scientists discovered recently that a phenomenon called a giant magnetic rope is the cause of solar storms. Confirming the existence of this formation is a key first step in helping to mitigate the adverse effects that solar storm eruptions can have on satellite communications on Earth.

The discovery was made by associate professor Jie Zhang and his graduate student Xin Cheng using images from the NASA Solar Dynamic Observatory (SDO) spacecraft.

Though the magnetic rope was believed to be the cause of these giant eruptions on the Sun, scientists had previously not been able to prove this phenomenon existed because of how quickly the rope moves.

However, through close examination of images taken by the Atmospheric Imaging Assembly (AIA) telescope on board the SDO, Zhang was able to pinpoint an area of the sun where a magnetic rope was forming. The AIA telescope suite is able to capture images of the Sun every 10 seconds, 24 hours a day. This unprecedented cadence in time helped the discovery.

"The magnetic rope triggers a solar eruption. Scientists have been debating whether or not this magnetic rope exists before a solar eruption. I believe that the result of this excellent observation helps finally solve this controversial issue," says Zhang.

A solar storm is a violent eruption from the Sun, sending billions of tons of charged material, also called plasma, into space at a speed of more than one million miles per hour. The cloud of plasma carries with it a strong magnetic field. When the magnetized cloud reaches Earth one to three days later, a huge amount of energy is deposited into the magnetosphere of Earth.

Normally Earth's magnetosphere shields this harmful solar wind and protects the environment. However, a solar storm has the potential to disrupt the shielding effect and produce severe space weather, which can have harmful effects on a wide array of technological systems, including satellite operation, communication and navigation and electric power grids.

Zhang's research will help in giving early warning about solar storms and help to minimize the damage done by space weather here on Earth.

"Understanding the eruption process of these storms will definitely help us better predict them," says Zhang. "We cannot prevent solar storms, just like we cannot prevent earthquakes or volcanoes. But the development of prediction capacity can help mitigate adverse effects. For instance, satellite operators can power-down key systems to prevent the possible damage to the systems."

It is widely believed that magnetic fields in the Sun play an essential role in storing energy and powering solar storms. However, the exact form that magnetic field lines take prior to the eruption are highly controversial. Most field lines are semi-circular loops with their foot-points rooted on the surface of the Sun. They cannot erupt easily, and in fact, they often play the role of preventing the eruption.

Scientists suspected that the magnetic rope, if it indeed existed, was the phenomenon that powered the eruption. A magnetic rope contains many magnetic field lines wrapping around a center axis and possibly twisting around each other. Because of the twisting, a strong electric current can be carried by the magnetic rope. Theoretically, the electric current could produce a sufficient electro-magnetic force to overcome the overlying constraining force from other field lines and power the magnetic rope to move outward.

AIA images now reveal that, before an eruption, there is a long and low-lying channel running through the entire active region, which heats to a temperature as high as 10 million degrees, and slowly rises. When it reaches a critical point, it starts to erupt quickly. It is a feature distinctly different from the surrounding magnetic field lines. This particular hot channel is now believed to be the magnetic rope that scientists have been looking for.

Zhang is an associate professor in the School of Physics, Astronomy and Computational Sciences and works with the Space Weather Lab at George Mason University. His results were reported at the American Astronomical Society Solar Physics Division Meeting, held in Las Cruces, New Mexico on June 12-16, 2011.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by George Mason University.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Using magnets to help prevent heart attacks: Magnetic field can reduce blood viscosity, physicist discovers

ScienceDaily (June 8, 2011) — If a person's blood becomes too thick it can damage blood vessels and increase the risk of heart attacks. But a Temple University physicist has discovered that he can thin the human blood by subjecting it to a magnetic field.

Rongjia Tao, professor and chair of physics at Temple University, has pioneered the use of electric or magnetic fields to decrease the viscosity of oil in engines and pipelines. Now, he is using the same magnetic fields to thin human blood in the circulation system.

Because red blood cells contain iron, Tao has been able to reduce a person's blood viscosity by 20-30 percent by subjecting it to a magnetic field of 1.3 Telsa (about the same as an MRI) for about one minute.

Tao and his collaborator tested numerous blood samples in a Temple lab and found that the magnetic field polarizes the red blood cells causing them to link together in short chains, streamlining the movement of the blood. Because these chains are larger than the single blood cells, they flow down the center, reducing the friction against the walls of the blood vessels. The combined effects reduce the viscosity of the blood, helping it to flow more freely.

When the magnetic field was taken away, the blood's original viscosity state slowly returned, but over a period of several hours.

"By selecting a suitable magnetic field strength and pulse duration, we will be able to control the size of the aggregated red-cell chains, hence to control the blood's viscosity," said Tao. "This method of magneto-rheology provides an effective way to control the blood viscosity within a selected range."

Currently, the only method for thinning blood is through drugs such as aspirin; however, these drugs often produce unwanted side effects. Tao said that the magnetic field method is not only safer, it is repeatable. The magnetic fields may be reapplied and the viscosity reduced again. He also added that the viscosity reduction does not affect the red blood cells' normal function.

Tao said that further studies are needed and that he hopes to ultimately develop this technology into an acceptable therapy to prevent heart disease.

Tao and his former graduate student, Ke "Colin" Huang, now a medical physics resident in the Department of Radiation Oncology at the University of Michigan, are publishing their findings in the journal Physical Review E.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Temple University, via EurekAlert!, a service of AAAS.

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Magnetic bubbles reside at solar system edge, NASA probes suggest

ScienceDaily (June 9, 2011) — Observations from NASA's Voyager spacecraft, humanity's farthest deep space sentinels, suggest the edge of our solar system may not be smooth, but filled with a turbulent sea of magnetic bubbles.

While using a new computer model to analyze Voyager data, scientists found the sun's distant magnetic field is made up of bubbles approximately 100 million miles wide. The bubbles are created when magnetic field lines reorganize. The new model suggests the field lines are broken up into self-contained structures disconnected from the solar magnetic field. The findings are described in the June 9 edition of the Astrophysical Journal.

Like Earth, our sun has a magnetic field with a north pole and a south pole. The field lines are stretched outward by the solar wind or a stream of charged particles emanating from the star that interacts with material expelled from others in our corner of the Milky Way galaxy.

The Voyager spacecraft, nearly 10 billion miles away from Earth, are traveling in a boundary region. In that area, the solar wind and magnetic field are affected by material expelled from other stars in our corner of the Milky Way galaxy.

"The sun's magnetic field extends all the way to the edge of the solar system," said astronomer Merav Opher of Boston University. "Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are, the folds of the skirt bunch up."

Understanding the structure of the sun's magnetic field will allow scientists to explain how galactic cosmic rays enter our solar system and help define how the star interacts with the rest of the galaxy.

So far, much of the evidence for the existence of the bubbles originates from an instrument aboard the spacecraft that measures energetic particles. Investigators are studying more information and hoping to find signatures of the bubbles in the Voyager magnetic field data.

"We are still trying to wrap our minds around the implications of the findings," said University of Maryland physicist Jim Drake, one of Opher's colleagues.

Launched in 1977, the Voyager twin spacecraft have been on a 33-year journey. They are en route to reach the edge of interstellar space. NASA's Jet Propulsion Laboratory in Pasadena, Calif., built the spacecraft and continues to operate them. The Voyager missions are a part of the Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's Science Mission Directorate in Washington.

To view supporting images about the research, visit: http://www.nasa.gov/sunearth

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA.

Journal Reference:

Fathallah Alouani-Bibi, Merav Opher, Dimitry Alexashov, Vladislav Izmodenov, Gabor Toth. Kinetic versus Multi-fluid Approach for Interstellar Neutrals in the Heliosphere: Exploration of the Interstellar Magnetic Field Effects. The Astrophysical Journal, 2011; 734 (1): 45 DOI: 10.1088/0004-637X/734/1/45

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Magnetic bubbles reside at solar system edge, NASA probes suggest

ScienceDaily (June 9, 2011) — Observations from NASA's Voyager spacecraft, humanity's farthest deep space sentinels, suggest the edge of our solar system may not be smooth, but filled with a turbulent sea of magnetic bubbles.

While using a new computer model to analyze Voyager data, scientists found the sun's distant magnetic field is made up of bubbles approximately 100 million miles wide. The bubbles are created when magnetic field lines reorganize. The new model suggests the field lines are broken up into self-contained structures disconnected from the solar magnetic field. The findings are described in the June 9 edition of the Astrophysical Journal.

Like Earth, our sun has a magnetic field with a north pole and a south pole. The field lines are stretched outward by the solar wind or a stream of charged particles emanating from the star that interacts with material expelled from others in our corner of the Milky Way galaxy.

The Voyager spacecraft, nearly 10 billion miles away from Earth, are traveling in a boundary region. In that area, the solar wind and magnetic field are affected by material expelled from other stars in our corner of the Milky Way galaxy.

"The sun's magnetic field extends all the way to the edge of the solar system," said astronomer Merav Opher of Boston University. "Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are, the folds of the skirt bunch up."

Understanding the structure of the sun's magnetic field will allow scientists to explain how galactic cosmic rays enter our solar system and help define how the star interacts with the rest of the galaxy.

So far, much of the evidence for the existence of the bubbles originates from an instrument aboard the spacecraft that measures energetic particles. Investigators are studying more information and hoping to find signatures of the bubbles in the Voyager magnetic field data.

"We are still trying to wrap our minds around the implications of the findings," said University of Maryland physicist Jim Drake, one of Opher's colleagues.

Launched in 1977, the Voyager twin spacecraft have been on a 33-year journey. They are en route to reach the edge of interstellar space. NASA's Jet Propulsion Laboratory in Pasadena, Calif., built the spacecraft and continues to operate them. The Voyager missions are a part of the Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's Science Mission Directorate in Washington.

To view supporting images about the research, visit: http://www.nasa.gov/sunearth

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA.

Journal Reference:

Fathallah Alouani-Bibi, Merav Opher, Dimitry Alexashov, Vladislav Izmodenov, Gabor Toth. Kinetic versus Multi-fluid Approach for Interstellar Neutrals in the Heliosphere: Exploration of the Interstellar Magnetic Field Effects. The Astrophysical Journal, 2011; 734 (1): 45 DOI: 10.1088/0004-637X/734/1/45

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Researchers discover superatoms with magnetic shells

ScienceDaily (June 9, 2011) — A team of Virginia Commonwealth University scientists has discovered a new class of 'superatoms' -- a stable cluster of atoms that can mimic different elements of the periodic table -- with unusual magnetic characteristics.

The superatom contains magnetized magnesium atoms, an element traditionally considered as non-magnetic. The metallic character of magnesium along with infused magnetism may one day be used to create molecular electronic devices for the next generation of faster processors, larger memory storage and quantum computers.

In a study published online in the Early Edition of the Proceedings of the National Academy of Sciences, the team reports that the newly discovered cluster consisting of one iron and eight magnesium atoms acts like a tiny magnet that derives its magnetic strength from the iron and magnesium atoms. The combined unit matches the magnetic strength of a single iron atom while preferentially allowing electrons of specific spin orientation to be distributed throughout the cluster.

Through an elaborate series of theoretical studies, Shiv N. Khanna, Ph.D., a Commonwealth professor in the VCU Department of Physics, and his team examined the electronic and magnetic properties of clusters having one iron atom surrounded by multiple magnesium atoms. The team included instructor J. Ulises Reveles and Victor M. Medel, a post-doctoral associate, both from VCU; A. W. Castleman Jr., Ph.D., the Evan Pugh Professor of Chemistry and Physics, and Eberly Distinguished chair in Science in the Department of Chemistry at Penn State University; and Prasenjit Sen and Vikas Chauhan from the Harish-Chandra Research Institute in Allahabad, India.

"Our research opens a new way of infusing magnetic character in otherwise non-magnetic elements through controlled association with a single magnetic atom. An important objective was to discover what combination of atoms would lead to a species that is stable as we put multiple units together," said Khanna.

"The combination of magnetic and conducting attributes was also desirable. Magnesium is a good conductor of electricity and, hence, the superatom combines the benefit of magnetic character along with ease of conduction through its outer skin," he said.

The team found that when the cluster had eight magnesium atoms it acquired extra stability due to filled electronic shells that were far separated from the unfilled shells. An atom is in a stable configuration when its outermost shell is full and far separated from unfilled shells, as found in inert gas atoms. Khanna said that such phenomena commonly occur with paired electrons which are non-magnetic, but in this study the magnetic electronic shell showed stability.

According to Khanna, the new cluster had a magnetic moment of four Bohr magnetons, which is almost twice that of an iron atom in solid iron magnets. A magnetic moment is a measure of the magnetic strength of the cluster. Although the periodic table has more than one hundred elements, there are only nine elements that exhibit magnetic character in solid form.

"A combination such as the one we have created here can lead to significant developments in the area of "molecular electronics" where such devices allow the flow of electrons with particular spin orientation desired for applications such as quantum computers. These molecular devices are also expected to help make denser integrated devices, higher data processing, and other benefits," said Reveles.

Khanna and his team are conducting preliminary studies on the assemblies of the new superatoms and have made some promising observations that may have applications in spintronics. Spintronics is a process using electron spin to synthesize new devices for memory and data processing.

This research was supported by the U.S. Department of Energy.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Virginia Commonwealth University.

Journal Reference:

Victor M. Medel, Jose Ulises Reveles, Shiv N. Khanna, Vikas Chauhan, Prasenjit Sen, A. Welford Castleman. Hund's rule in superatoms with transition metal impurities. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1100129108

Note: If no author is given, the source is cited instead.

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Nuclear magnetic resonance with no magnets

ScienceDaily (May 19, 2011) — Nuclear magnetic resonance (NMR), a scientific technique associated with outsized, very low-temperature, superconducting magnets, is one of the principal tools in the chemist's arsenal, used to study everything from alcohols to proteins to such frontiers as quantum computing. In hospitals the machinery of NMR's cousin, magnetic resonance imaging (MRI), is as loud as it is big, but nevertheless a mainstay of diagnosis for a wide range of medical conditions.

It sounds like magic, but now two groups of scientists at Berkeley Lab and UC Berkeley, one expert in chemistry and the other in atomic physics, long working together as a multidisciplinary team, have shown that chemical analysis with NMR is practical without using any magnets at all.

Dmitry Budker of Berkeley Lab's Nuclear Science Division, a professor of physics at UC Berkeley, is a protean experimenter who leads a group with interests ranging as far afield as tests of the fundamental theorems of quantum mechanics, biomagnetism in plants, and violations of basic symmetry relations in atomic nuclei. Alex Pines, of the Lab's Materials Sciences Division and UCB's Department of Chemistry, is a modern master of NMR and MRI. He guides the work of a talented, ever-changing cadre of postdocs and grad students known as the "Pinenuts" -- not only in doing basic research in NMR but in increasing its practical applications. Together the groups have extended the reach of NMR by eliminating the use of magnetic fields at different stages of NMR measurements, and have finally done away with external magnetic fields entirely.

Spinning the information

NMR and MRI depend on the fact that many atomic nuclei possess spin (not classical rotation but a quantum number) and -- like miniature planet Earths with north and south magnetic poles -- have their own dipolar magnetic fields. In conventional NMR these nuclei are lined up by a strong external magnetic field, then knocked off axis by a burst of radio waves. The rate at which each kind of nucleus then "wobbles" (precesses) is unique and identifies the element; for example a hydrogen-1 nucleus, a lone proton, precesses four times faster than a carbon-13 nucleus having six protons and seven neutrons.

Being able to detect these signals depends first of all on being able to detect net spin; if the sample were to have as many spin-up nuclei as spin-down nuclei it would have zero polarization, and signals would cancel. But since the spin-up orientation requires slightly less energy, a population of atomic nuclei usually has a slight excess of spin ups, if only by a few score in a million.

"Conventional wisdom holds that trying to do NMR in weak or zero magnetic fields is a bad idea," says Budker, "because the polarization is tiny, and the ability to detect signals is proportional to the strength of the applied field."

The lines in a typical NMR spectrum reveal more than just different elements. Electrons near precessing nuclei alter their precession frequencies and cause a "chemical shift" -- moving the signal or splitting it into separate lines in the NMR spectrum. This is the principal goal of conventional NMR, because chemical shifts point to particular chemical species; for example, even when two hydrocarbons contain the same number of hydrogen, carbon, or other atoms, their signatures differ markedly according to how the atoms are arranged. But without a strong magnetic field, chemical shifts are insignificant.

"Low- or zero-field NMR starts with three strikes against it: small polarization, low detection efficiency, and no chemical-shift signature," Budker says.

"So why do it?" asks Micah Ledbetter of Budker's group. It's a rhetorical question. "The main thing is getting rid of the big, expensive magnets needed for conventional NMR. If you can do that, you can make NMR portable and reduce the costs, including the operating costs. The hope is to be able to do chemical analyses in the field -- underwater, down drill holes, up in balloons -- and maybe even medical diagnoses, far from well-equipped medical centers."

"As it happens," Budker says, "there are already methods for overcoming small polarization and low detection efficiency, the first two objections to low- or zero-field NMR. By bringing these separate methods together, we can tackle the third objection -- no chemical shift -- as well. Zero-field NMR may not be such a bad idea after all."

Net spin orientation can be increased in various ways, collectively known as hyperpolarization. One way to hyperpolarize a sample of hydrogen gas is to change the proportions of parahydrogen and orthohydrogen in it. Like most gases, at normal temperature and pressure each hydrogen molecule consists of two atoms bound together. If the spins of the proton nuclei point in the same direction, it's orthohydrogen. If the spins point in opposite directions, it's parahydrogen.

By the mathematics of quantum mechanics, adding up the spin states of the two protons and two electrons in a hydrogen molecule equals three ways for orthohydrogen to reach spin one; parahydrogen can only be spin zero, however. Thus orthohydrogen molecules normally account for three-quarters of hydrogen gas and parahydrogen only one-quarter.

Parahydrogen can be enhanced to 50 percent or even 100 percent using very low temperatures, although the right catalyst must be added or the conversion could take days if not weeks. Then, by chemically reacting spin-zero parahydrogen molecules with an initial chemical, net polarization of the product of the hydrogenation may end up highly polarized. This hyperpolarization can be extended not only to the parts of the molecule directly reacting with the hydrogen, but even to the far corners of large molecules. The Pinenuts, who devised many of the techniques, are masters of parahydrogen production and its hyperpolarization chemistry.

"With a high proportion of parahydrogen you get a terrific degree of polarization," says Ledbetter. "The catch is, it's spin zero. It doesn't have a magnetic moment, so it doesn't give you a signal! But all is not lost…."

And now for the magic

In low magnetic fields, increasing detection efficiency requires a very different approach, using detectors called magnetometers. In early low-field experiments, magnetometers called SQUID were used (superconducting quantum interference devices). Although exquisitely sensitive, SQUID, like the big magnets used in high-field NMR, must be cryogenically cooled to low temperatures.

Optical-atomic magnetometers are based on a different principle -- one that, curiously, is something like NMR in reverse, except that optical-atomic magnetometers measure whole atoms, not just nuclei. Here, an external magnetic field is measured by measuring the spin of the atoms inside the magnetometer's own vapor cell, typically a thin gas of an alkali metal such as potassium or rubidium. Their spin is influenced by polarizing the atoms with laser light; if there's even a weak external field, they begin to precess. A second laser beam probes how much they're precessing and thus just how strong the external field is.

Budker's group has brought optical-atomic magnetometry to a high pitch by such techniques as extending the "relaxation time," the time before the polarized vapor loses its polarization. In previous collaborations, the Pines and Budker groups have used magnetometers with NMR and MRI to image the flow of water using only the Earth's magnetic field or no field at all, to detect hyperpolarized xenon gas (but without analyzing chemical states), and in other applications. The next frontier is chemical analysis.

"No matter how sensitive your detector or how polarized your samples, you can't detect chemical shifts in a zero field," Budker says. "But there has always been another signal in NMR that can be used for chemical analysis -- it's just that it is usually so weak compared to chemical shifts, it has been the poor relative in the NMR family. It's called J-coupling."

Discovered in 1950 by the NMR pioneer Erwin Hahn and his graduate student, Donald Maxwell, J-coupling provides an interaction pathway between two protons (or other nuclei with spin), which is mediated by their associated electrons. The signature frequencies of these interactions, appearing in the NMR spectrum, can be used to determine the angle between chemical bonds and distances between the nuclei.

"You can even tell how many bonds separate the two spins," Ledbetter says. "J-coupling reveals all that information."

The resulting signals are highly specific and indicate just what chemical species is being observed. Moreover, as Hahn saw right away, while the signal can be modified by external magnetic fields, it does not vanish in their absence.

With Ledbetter in the lead, the Budker/Pines collaboration built a magnetometer specifically designed to detect J-coupling at zero magnetic field. Thomas Theis, a graduate student in the Pines group, supplied the parahydrogen and the chemical expertise to take advantage of parahydrogen-induced polarization. Beginning with styrene, a simple hydrocarbon, they measured J-coupling on a series of hydrocarbon derivatives including hexane and hexene, phenylpropene, and dimethyl maleate, important constituents of plastics, petroleum products, even perfumes.

"The first step is to introduce the parahydrogen," Budker says. "The top of the set-up is a test tube containing the sample solution, with a tube down to the bottom through which the parahydrogen is bubbled." In the case of styrene, the parahydrogen was taken up to produce ethylbenzene, a specific arrangement of eight carbon atoms and 10 hydrogen atoms.

Immediately below the test tube sits the magnetometer's alkali vapor cell, a device smaller than a fingernail, microfabricated by Svenja Knappe and John Kitching of the National Institute of Standards and Technology. The vapor cell, which sits on top of a heater, contains rubidium and nitrogen gas through which pump and probe laser beams cross at right angles. The mechanism is surrounded by cylinders of "mu metal," a nickel-iron alloy that acts as a shield against external magnetic fields, including Earth's.

Ledbetter's measurements produced signatures in the spectra which unmistakably identified chemical species and exactly where the polarized protons had been taken up. When styrene was hydrogenated to form ethylbenzene, for example, two atoms from a parahydrogen molecule bound to different atoms of carbon-13 (a scarce but naturally occurring isotope whose nucleus has spin, unlike more abundant carbon-12).

J-coupling signatures are completely different for otherwise identical molecules in which carbon-13 atoms reside in different locations. All of this is seen directly in the results. Says Budker, "When Micah goes into the laboratory, J-coupling is king."

Of the present football-sized magnetometer and its lasers, Ledbetter says, "We're already working on a much smaller version of the magnetometer that will be easy to carry into the field."

Although experiments to date have been performed on molecules that are easily hydrogenated, hyperpolarization with parahydrogen can also be extended to other kinds of molecules. Budker says, "We're just beginning to develop zero-field NMR, and it's still too early to say how well we're going to be able to compete with high-field NMR. But we've already shown that we can get clear, highly specific spectra, with a device that has ready potential for doing low-cost, portable chemical analysis."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

T. Theis, P. Ganssle, G. Kervern, S. Knappe, J. Kitching, M. P. Ledbetter, D. Budker, A. Pines. Parahydrogen-enhanced zero-field nuclear magnetic resonance. Nature Physics, 2011; DOI: 10.1038/nphys1986

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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Nuclear magnetic resonance with no magnets

ScienceDaily (May 19, 2011) — Nuclear magnetic resonance (NMR), a scientific technique associated with outsized, very low-temperature, superconducting magnets, is one of the principal tools in the chemist's arsenal, used to study everything from alcohols to proteins to such frontiers as quantum computing. In hospitals the machinery of NMR's cousin, magnetic resonance imaging (MRI), is as loud as it is big, but nevertheless a mainstay of diagnosis for a wide range of medical conditions.

It sounds like magic, but now two groups of scientists at Berkeley Lab and UC Berkeley, one expert in chemistry and the other in atomic physics, long working together as a multidisciplinary team, have shown that chemical analysis with NMR is practical without using any magnets at all.

Dmitry Budker of Berkeley Lab's Nuclear Science Division, a professor of physics at UC Berkeley, is a protean experimenter who leads a group with interests ranging as far afield as tests of the fundamental theorems of quantum mechanics, biomagnetism in plants, and violations of basic symmetry relations in atomic nuclei. Alex Pines, of the Lab's Materials Sciences Division and UCB's Department of Chemistry, is a modern master of NMR and MRI. He guides the work of a talented, ever-changing cadre of postdocs and grad students known as the "Pinenuts" -- not only in doing basic research in NMR but in increasing its practical applications. Together the groups have extended the reach of NMR by eliminating the use of magnetic fields at different stages of NMR measurements, and have finally done away with external magnetic fields entirely.

Spinning the information

NMR and MRI depend on the fact that many atomic nuclei possess spin (not classical rotation but a quantum number) and -- like miniature planet Earths with north and south magnetic poles -- have their own dipolar magnetic fields. In conventional NMR these nuclei are lined up by a strong external magnetic field, then knocked off axis by a burst of radio waves. The rate at which each kind of nucleus then "wobbles" (precesses) is unique and identifies the element; for example a hydrogen-1 nucleus, a lone proton, precesses four times faster than a carbon-13 nucleus having six protons and seven neutrons.

Being able to detect these signals depends first of all on being able to detect net spin; if the sample were to have as many spin-up nuclei as spin-down nuclei it would have zero polarization, and signals would cancel. But since the spin-up orientation requires slightly less energy, a population of atomic nuclei usually has a slight excess of spin ups, if only by a few score in a million.

"Conventional wisdom holds that trying to do NMR in weak or zero magnetic fields is a bad idea," says Budker, "because the polarization is tiny, and the ability to detect signals is proportional to the strength of the applied field."

The lines in a typical NMR spectrum reveal more than just different elements. Electrons near precessing nuclei alter their precession frequencies and cause a "chemical shift" -- moving the signal or splitting it into separate lines in the NMR spectrum. This is the principal goal of conventional NMR, because chemical shifts point to particular chemical species; for example, even when two hydrocarbons contain the same number of hydrogen, carbon, or other atoms, their signatures differ markedly according to how the atoms are arranged. But without a strong magnetic field, chemical shifts are insignificant.

"Low- or zero-field NMR starts with three strikes against it: small polarization, low detection efficiency, and no chemical-shift signature," Budker says.

"So why do it?" asks Micah Ledbetter of Budker's group. It's a rhetorical question. "The main thing is getting rid of the big, expensive magnets needed for conventional NMR. If you can do that, you can make NMR portable and reduce the costs, including the operating costs. The hope is to be able to do chemical analyses in the field -- underwater, down drill holes, up in balloons -- and maybe even medical diagnoses, far from well-equipped medical centers."

"As it happens," Budker says, "there are already methods for overcoming small polarization and low detection efficiency, the first two objections to low- or zero-field NMR. By bringing these separate methods together, we can tackle the third objection -- no chemical shift -- as well. Zero-field NMR may not be such a bad idea after all."

Net spin orientation can be increased in various ways, collectively known as hyperpolarization. One way to hyperpolarize a sample of hydrogen gas is to change the proportions of parahydrogen and orthohydrogen in it. Like most gases, at normal temperature and pressure each hydrogen molecule consists of two atoms bound together. If the spins of the proton nuclei point in the same direction, it's orthohydrogen. If the spins point in opposite directions, it's parahydrogen.

By the mathematics of quantum mechanics, adding up the spin states of the two protons and two electrons in a hydrogen molecule equals three ways for orthohydrogen to reach spin one; parahydrogen can only be spin zero, however. Thus orthohydrogen molecules normally account for three-quarters of hydrogen gas and parahydrogen only one-quarter.

Parahydrogen can be enhanced to 50 percent or even 100 percent using very low temperatures, although the right catalyst must be added or the conversion could take days if not weeks. Then, by chemically reacting spin-zero parahydrogen molecules with an initial chemical, net polarization of the product of the hydrogenation may end up highly polarized. This hyperpolarization can be extended not only to the parts of the molecule directly reacting with the hydrogen, but even to the far corners of large molecules. The Pinenuts, who devised many of the techniques, are masters of parahydrogen production and its hyperpolarization chemistry.

"With a high proportion of parahydrogen you get a terrific degree of polarization," says Ledbetter. "The catch is, it's spin zero. It doesn't have a magnetic moment, so it doesn't give you a signal! But all is not lost…."

And now for the magic

In low magnetic fields, increasing detection efficiency requires a very different approach, using detectors called magnetometers. In early low-field experiments, magnetometers called SQUID were used (superconducting quantum interference devices). Although exquisitely sensitive, SQUID, like the big magnets used in high-field NMR, must be cryogenically cooled to low temperatures.

Optical-atomic magnetometers are based on a different principle -- one that, curiously, is something like NMR in reverse, except that optical-atomic magnetometers measure whole atoms, not just nuclei. Here, an external magnetic field is measured by measuring the spin of the atoms inside the magnetometer's own vapor cell, typically a thin gas of an alkali metal such as potassium or rubidium. Their spin is influenced by polarizing the atoms with laser light; if there's even a weak external field, they begin to precess. A second laser beam probes how much they're precessing and thus just how strong the external field is.

Budker's group has brought optical-atomic magnetometry to a high pitch by such techniques as extending the "relaxation time," the time before the polarized vapor loses its polarization. In previous collaborations, the Pines and Budker groups have used magnetometers with NMR and MRI to image the flow of water using only the Earth's magnetic field or no field at all, to detect hyperpolarized xenon gas (but without analyzing chemical states), and in other applications. The next frontier is chemical analysis.

"No matter how sensitive your detector or how polarized your samples, you can't detect chemical shifts in a zero field," Budker says. "But there has always been another signal in NMR that can be used for chemical analysis -- it's just that it is usually so weak compared to chemical shifts, it has been the poor relative in the NMR family. It's called J-coupling."

Discovered in 1950 by the NMR pioneer Erwin Hahn and his graduate student, Donald Maxwell, J-coupling provides an interaction pathway between two protons (or other nuclei with spin), which is mediated by their associated electrons. The signature frequencies of these interactions, appearing in the NMR spectrum, can be used to determine the angle between chemical bonds and distances between the nuclei.

"You can even tell how many bonds separate the two spins," Ledbetter says. "J-coupling reveals all that information."

The resulting signals are highly specific and indicate just what chemical species is being observed. Moreover, as Hahn saw right away, while the signal can be modified by external magnetic fields, it does not vanish in their absence.

With Ledbetter in the lead, the Budker/Pines collaboration built a magnetometer specifically designed to detect J-coupling at zero magnetic field. Thomas Theis, a graduate student in the Pines group, supplied the parahydrogen and the chemical expertise to take advantage of parahydrogen-induced polarization. Beginning with styrene, a simple hydrocarbon, they measured J-coupling on a series of hydrocarbon derivatives including hexane and hexene, phenylpropene, and dimethyl maleate, important constituents of plastics, petroleum products, even perfumes.

"The first step is to introduce the parahydrogen," Budker says. "The top of the set-up is a test tube containing the sample solution, with a tube down to the bottom through which the parahydrogen is bubbled." In the case of styrene, the parahydrogen was taken up to produce ethylbenzene, a specific arrangement of eight carbon atoms and 10 hydrogen atoms.

Immediately below the test tube sits the magnetometer's alkali vapor cell, a device smaller than a fingernail, microfabricated by Svenja Knappe and John Kitching of the National Institute of Standards and Technology. The vapor cell, which sits on top of a heater, contains rubidium and nitrogen gas through which pump and probe laser beams cross at right angles. The mechanism is surrounded by cylinders of "mu metal," a nickel-iron alloy that acts as a shield against external magnetic fields, including Earth's.

Ledbetter's measurements produced signatures in the spectra which unmistakably identified chemical species and exactly where the polarized protons had been taken up. When styrene was hydrogenated to form ethylbenzene, for example, two atoms from a parahydrogen molecule bound to different atoms of carbon-13 (a scarce but naturally occurring isotope whose nucleus has spin, unlike more abundant carbon-12).

J-coupling signatures are completely different for otherwise identical molecules in which carbon-13 atoms reside in different locations. All of this is seen directly in the results. Says Budker, "When Micah goes into the laboratory, J-coupling is king."

Of the present football-sized magnetometer and its lasers, Ledbetter says, "We're already working on a much smaller version of the magnetometer that will be easy to carry into the field."

Although experiments to date have been performed on molecules that are easily hydrogenated, hyperpolarization with parahydrogen can also be extended to other kinds of molecules. Budker says, "We're just beginning to develop zero-field NMR, and it's still too early to say how well we're going to be able to compete with high-field NMR. But we've already shown that we can get clear, highly specific spectra, with a device that has ready potential for doing low-cost, portable chemical analysis."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

T. Theis, P. Ganssle, G. Kervern, S. Knappe, J. Kitching, M. P. Ledbetter, D. Budker, A. Pines. Parahydrogen-enhanced zero-field nuclear magnetic resonance. Nature Physics, 2011; DOI: 10.1038/nphys1986

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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