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  • richardmitnick 1:40 pm on January 3, 2019 Permalink | Reply
    Tags: A fundamental characteristic of electrons is their spin which points either up or down. A skyrmion is a circular cluster of electrons whose spins are opposite to the orientation of surrounding electro, , Dzyaloshinskii-Moriya interaction (DMI), Ferromagnets, , , Skyrmions, , tiny magnetic bits"   

    From MIT News: “Controllable fast, tiny magnetic bits” 

    MIT News
    MIT Widget

    From MIT News

    January 3, 2019
    Denis Paiste

    MIT researchers show how to make and drive nanoscale magnetic quasi-particles known as skyrmions for spintronic memory devices.

    1
    Work by researchers in the group of MIT materials science and engineering Professor Geoffrey Beach and colleagues in California, Germany, Switzerland and Korea, was featured on the covers of Nature Nanotechnology and Advanced Materials. Cover images reproduced with permission of the publishers.

    2
    Lucas Caretta (left) and Ivan Lemesh, graduate students in the lab of MIT professor of materials science and engineering Geoffrey Beach, each had a cover article in a peer-reviewed journal article in December. Their work is pioneering new directions for spintronic devices based on quasi-particles known as skyrmions. Photo: Denis Paiste/Materials Research Laboratory.

    For many modern technical applications, such as superconducting wires for magnetic resonance imaging, engineers want as much as possible to get rid of electrical resistance and its accompanying production of heat.

    It turns out, however, that a bit of heat production from resistance is a desirable characteristic in metallic thin films for spintronic applications such as solid-state computer memory. Similarly, while defects are often undesirable in materials science, they can be used to control creation of magnetic quasi-particles known as skyrmions.

    In separate papers published this month in the journals Nature Nanotechnology and Advanced Materials, researchers in the group of MIT Professor Geoffrey S.D. Beach and colleagues in California, Germany, Switzerland, and Korea, showed that they can generate stable and fast moving skyrmions in specially formulated layered materials at room temperature, setting world records for size and speed. Each paper was featured on the cover of its respective journal.

    For the research published in Advanced Materials [link is above], the researchers created a wire that stacks 15 repeating layers of a specially fabricated metal alloy made up of platinum, which is a heavy metal, cobalt-iron-boron, which is a magnetic material, and magnesium-oxygen. In these layered materials, the interface between the platinum metal layer and cobalt-iron-boron creates an environment in which skyrmions can be formed by applying an external magnetic field perpendicular to the film and electric current pulses that travel along the length of the wire.

    Notably, under a 20 milliTesla field, a measure of the magnetic field strength, the wire forms skyrmions at room temperature. At temperatures above 349 kelvins (168 degrees Fahrenheit), the skyrmions form without an external magnetic field, an effect caused by the material heating up, and the skyrmions remain stable even after the material is cooled back to room temperature. Previously, results like this had been seen only at low temperature and with large applied magnetic fields, Beach says.

    Predictable structure

    “After developing a number of theoretical tools, we now can not only predict the internal skyrmion structure and size, but we also can do a reverse engineering problem, we can say, for instance, we want to have a skyrmion of that size, and we’ll be able to generate the multi-layer, or the material, parameters, that would lead to the size of that skyrmion,” says Ivan Lemesh, first author of the Advanced Materials paper and a graduate student in materials science and engineering at MIT. Co-authors include senior author Beach and 17 others.

    A fundamental characteristic of electrons is their spin, which points either up or down. A skyrmion is a circular cluster of electrons whose spins are opposite to the orientation of surrounding electrons, and the skyrmions maintain a clockwise or counter-clockwise direction.

    “However, on top of that, we have also discovered that skyrmions in magnetic multilayers develop a complex through-thickness dependent twisted nature,” Lemesh said during a presentation on his work at the Materials Research Society (MRS) fall meeting in Boston on Nov. 30. Those findings were published in a separate theoretical study in Physical Review B in September.

    The current research shows that while this twisted structure of skyrmions has a minor impact on the ability to calculate the average size of the skyrmion, it significantly affects their current-induced behavior.

    Fundamental limits

    For the paper in Nature Nanotechnology [link is above], the researchers studied a different magnetic material, layering platinum with a magnetic layer of a gadolinium cobalt alloy, and tantalum oxide. In this material, the researchers showed they could produce skyrmions as small as 10 nanometers and established that they could move at a fast speed in the material.

    “What we discovered in this paper is that ferromagnets have fundamental limits for the size of the quasi-particle you can make and how fast you can drive them using currents,” says first author Lucas Caretta, a graduate student in materials science and engineering.

    In a ferromagnet, such as cobalt-iron-boron, neighboring spins are aligned parallel to one another and develop a strong directional magnetic moment. To overcome the fundamental limits of ferromagnets, the researchers turned to gadolinium-cobalt, which is a ferrimagnet, in which neighboring spins alternate up and down so they can cancel each other out and result in an overall zero magnetic moment.

    “One can engineer a ferrimagnet such that the net magnetization is zero, allowing ultrasmall spin textures, or tune it such that the net angular momentum is zero, enabling ultrafast spin textures. These properties can be engineered by material composition or temperature,” Caretta explains.

    In 2017, researchers in Beach’s group and their collaborators demonstrated experimentally that they could create these quasi-particles at will in specific locations by introducing a particular kind of defect in the magnetic layer.

    “You can change the properties of a material by using different local techniques such as ion bombardment, for instance, and by doing that you change its magnetic properties,” Lemesh says, “and then if you inject a current into the wire, the skyrmion will be born in that location.”

    Adds Caretta: “It was originally discovered with natural defects in the material, then they became engineered defects through the geometry of the wire.”

    They used this method to create skyrmions in the new Nature Nanotechnology [link is above] paper.

    The researchers made images of the skyrmions in the cobalt-gadolinium mixture at room temperature at synchrotron centers in Germany, using X-ray holography. Felix Büttner, a postdoc in the Beach lab, was one of the developers of this X-ray holography technique. “It’s one of the only techniques that can allow for such highly resolved images where you make out skyrmions of this size,” Caretta says.

    These skyrmions are as small as 10 nanometers, which is the current world record for room temperature skyrmions. The researchers demonstrated current driven domain wall motion of 1.3 kilometers per second, using a mechanism that can also be used to move skyrmions, which also sets a new world record.

    Except for the synchrotron work, all the research was done at MIT. “We grow the materials, do the fabrication and characterize the materials here at MIT,” Caretta says.

    Magnetic modeling

    These skyrmions are one type of spin configuration of electron spins in these materials, while domain walls are another. Domain walls are the boundary between domains of opposing spin orientation. In the field of spintronics, these configurations are known as solitons, or spin textures. Since skyrmions are a fundamental property of materials, mathematical characterization of their energy of formation and motion involves a complex set of equations incorporating their circular size, spin angular momentum, orbital angular momentum, electronic charge, magnetic strength, layer thickness, and several special physics terms that capture the energy of interactions between neighboring spins and neighboring layers, such as the exchange interaction.

    One of these interactions, which is called the Dzyaloshinskii-Moriya interaction (DMI), is of special significance to forming skyrmions and arises from the interplay between electrons in the platinum layer and the magnetic layer. In the Dzyaloshinskii-Moriya interaction, spins align perpendicular to each other, which stabilizes the skyrmion, Lemesh says. The DMI interaction allows for these skyrmions to be topological, giving rise to fascinating physics phenomena, making them stable, and allowing for them to be moved with a current.

    “The platinum itself is what provides what’s called a spin current which is what drives the spin textures into motion,” Caretta says. “The spin current provides a torque on the magnetization of the ferro or ferrimagnet adjacent to it, and this torque is what ultimately causes the motion of the spin texture. We’re basically using simple materials to realize complicated phenomena at interfaces.”

    In both papers, the researchers performed a mix of micromagnetic and atomistic spin calculations to determine the energy required to form skyrmions and to move them.

    “It turns out that by changing the fraction of a magnetic layer, you can change the average magnetic properties of the whole system, so now we don’t need to go to a different material to generate other properties,” Lemesh says. “You can just dilute the magnetic layer with a spacer layer of different thickness, and you will wind up with different magnetic properties, and that gives you an infinite number of opportunities to fabricate your system.”

    Precise control

    “Precise control of creating magnetic skyrmions is a central topic of the field,” says Jiadong Zang, an assistant professor of physics at the University of New Hampshire, who was not involved in this research, regarding the Advanced Materials paper. “This work has presented a new way of generating zero field skyrmions via current pulse. This is definitely a solid step towards skyrmion manipulations in nanosecond regime.”

    Commenting on the Nature Nanotechnology report, Christopher Marrows, a professor of condensed matter physics at the University of Leeds in the United Kingdom says: “The fact that the skyrmions are so small but can be stabilized at room temperature makes it very significant.”

    Marrows, who also was not involved in this research, noted that the Beach group had predicted room temperature skyrmions in a Scientific Reports paper earlier this year and said the new results are work of the highest quality. “But they made the prediction and real life does not always live up to theoretical expectations, so they deserve all the credit for this breakthrough,” Marrows says.

    Zang, commenting on the Nature Nanotechnology paper, adds: “A bottleneck of skyrmion study is to reach a size of smaller than 20 nanometers [the size of state-of-art memory unit], and drive its motion with speed beyond one kilometer per second. Both challenges have been tackled in this seminal work.

    “A key innovation is to use ferrimagnet, instead of commonly used ferromagnet, to host skyrmions,” Zang says. “This work greatly stimulates the design of skyrmion-based memory and logic devices. This is definitely a star paper in the skyrmion field.”

    Racetrack systems

    Solid-state devices built on these skyrmions could someday replace current magnetic storage hard drives. Streams of magnetic skyrmions can act as bits for computer applications. “In these materials, we can readily pattern magnetic tracks,” Beach said during a presentation at MRS.

    These new findings could be applied to racetrack memory devices, which were developed by Stuart Parkin at IBM. A key to engineering these materials for use in racetrack devices is engineering deliberate defects into the material where skyrmions can form, because skyrmions form where there are defects in the material.

    “One can engineer by putting notches in this type of system,” said Beach, who also is co-director of the Materials Research Laboratory (MRL) at MIT. A current pulse injected into the material forms the skyrmions at a notch. “The same current pulse can be used to write and delete,” he said. These skyrmions form extremely quickly, in less than a billionth of a second, Beach says.

    Says Caretta: “To be able to have a practical operating logic or memory racetrack device, you have to write the bit, so that’s what we talk about in creating the magnetic quasi particle, and you have to make sure that the written bit is very small and you have to translate that bit through the material at a very fast rate,” Caretta says.

    Marrows, the Leeds professor, adds: “Applications in skyrmion-based spintronics, will benefit, although again it’s a bit early to say for sure what will be the winners among the various proposals, which include memories, logic devices, oscillators and neuromorphic devices,”

    A remaining challenge is the best way to read these skyrmion bits. Work in the Beach group is continuing in this area, Lemesh says, noting that the current challenge is to discover a way to detect these skyrmions electrically in order to use them in computers or phones.

    “Yea, so you don’t have to take your phone to a synchrotron to read a bit,” Caretta says. “As a result of some of the work done on ferrimagnets and similar systems called anti-ferromagnets, I think the majority of the field will actually start to shift toward these types of materials because of the huge promise that they hold.”

    See the full article here .


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  • richardmitnick 10:38 am on March 7, 2018 Permalink | Reply
    Tags: , , , , , Skyrmions, Weird quantum particles simulated in droplet of ultracold gas   

    From Science Magazine: “Weird quantum particles simulated in droplet of ultracold gas” 

    AAAS
    Science Magazine

    Mar. 2, 2018
    Randall Hyman

    1
    Heikka Valja

    In physics, theorists are often way ahead of the curve in describing what weird quantum particles could and should exist. Now, physicists in the United States and Finland have teamed up to create an incarnation of a quasi-particle called a skyrmion, first proposed in 1962 by U.K. physicist and mathematician Tony Skyrme as a model of real protons and neutrons. A skyrmion isn’t a fundamental particle that “bops you over the head” like a quark or a muon, says physicist David Hall of Amherst College in Massachusetts. Instead, it’s a localized excitation in space, made in a field of spins. The result is a kind of self-reinforcing knot, a bit like a Mobius strip that can’t be torn apart except by extreme force. By precisely controlling electromagnetic coils surrounding a glass vacuum chamber filled with superfluid rubidium, the team created 3D skyrmions for the first time ever. Their shadowy photographs depict a droplet of 200,000 supercooled rubidium atoms, a few 10-billionths of a degree above absolute zero. What’s more, the atoms revealed the very spin profiles Skyrme predicted, held together by a looping magnetic field. Oddly, the discovery, reported in Science Advances, could yield insight into ball lightning, a rare and controversial electrical phenomenon that supposedly forms balls of electricity meters across that can float through walls and suddenly discharge like dynamite. One theory holds that ball lightning, like skyrmions, may be held together by electromagnetically knotted fields that are surprisingly stable.

    See the full article here .

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    • Michael McLaughlin 10:47 am on March 7, 2018 Permalink | Reply

      Fantastic article! I would love to see a near absolute zero apparatus to see how they freeze these particle for observation.

      Like

  • richardmitnick 3:32 pm on October 6, 2017 Permalink | Reply
    Tags: , , , Skyrmions   

    From MIT: “Fast-moving magnetic particles could enable new form of data storage” 

    MIT News

    MIT Widget

    MIT News

    October 2, 2017
    David Chandler

    1
    “One of the biggest missing pieces” needed to make skyrmions a practical data-storage medium, Geoffrey Beach says, was a reliable way to create them when and where they were needed. “So this is a significant breakthrough.” Illustration by Moritz Eisebitt.

    Recently discovered phenomenon could provide a way to bypass the limits to Moore’s Law.

    New research has shown that an exotic kind of magnetic behavior discovered just a few years ago holds great promise as a way of storing data — one that could overcome fundamental limits that might otherwise be signaling the end of “Moore’s Law,” which describes the ongoing improvements in computation and data storage over recent decades.

    Rather than reading and writing data one bit at a time by changing the orientation of magnetized particles on a surface, as today’s magnetic disks do, the new system would make use of tiny disturbances in magnetic orientation, which have been dubbed “skyrmions.” These virtual particles, which occur on a thin metallic film sandwiched against a film of different metal, can be manipulated and controlled using electric fields, and can store data for long periods without the need for further energy input.

    In 2016, a team led by MIT associate professor of materials science and engineering Geoffrey Beach documented the existence of skyrmions, but the particles’ locations on a surface were entirely random. Now, Beach has collaborated with others to demonstrate experimentally for the first time that they can create these particles at will in specific locations, which is the next key requirement for using them in a data storage system. An efficient system for reading that data will also be needed to create a commercializable system.

    The new findings are reported this week in the journal Nature Nanotechnology, in a paper by Beach, MIT postdoc Felix Buettner, and graduate student Ivan Lemesh, and 10 others at MIT and in Germany.

    The system focuses on the boundary region between atoms whose magnetic poles are pointing in one direction and those with poles pointing the other way. This boundary region can move back and forth within the magnetic material, Beach says. What he and his team found four years ago was that these boundary regions could be controlled by placing a second sheet of nonmagnetic heavy metal very close to the magnetic layer. The nonmagnetic layer can then influence the magnetic one, with electric fields in the nonmagnetic layer pushing around the magnetic domains in the magnetic layer. Skyrmions are little swirls of magnetic orientation within these layers, Beach adds.

    The key to being able to create skyrmions at will in particular locations, it turns out, lay in material defects. By introducing a particular kind of defect in the magnetic layer, the skyrmions become pinned to specific locations on the surface, the team found. Those surfaces with intentional defects can then be used as a controllable writing surface for data encoded in the skyrmions. The team realized that instead of being a problem, the defects in the material could actually be beneficial.

    “One of the biggest missing pieces” needed to make skyrmions a practical data-storage medium, Beach says, was a reliable way to create them when and where they were needed. “So this is a significant breakthrough,” he explains, thanks to work by Buettner and Lemesh, the paper’s lead authors. “What they discovered was a very fast and efficient way to write” such formations.

    Because the skyrmions, basically little eddies of magnetism, are incredibly stable to external perturbations, unlike the individual magnetic poles in a conventional magnetic storage device, data can be stored using only a tiny area of the magnetic surface — perhaps just a few atoms across. That means that vastly more data could be written onto a surface of a given size. That’s an important quality, Beach explains, because conventional magnetic systems are now reaching limits set by the basic physics of their materials, potentially bringing to a halt the steady improvement of storage capacities that are the basis for Moore’s Law. The new system, once perfected, could provide a way to continue that progress toward ever-denser data storage, he says.

    The system also potentially could encode data at very high speeds, making it efficient not only as a substitute for magnetic media such as hard discs, but even for the much faster memory systems used in Random Access Memory (RAM) for computation.

    But what is still lacking is an effective way to read out the data once it has been stored. This can be done now using sophisticated X-ray magnetic spectroscopy, but that requires equipment too complex and expensive to be part of a practical computer memory system. The researchers plan to explore better ways of getting the information back out, which could be practical to manufacture at scale.

    The X-ray spectrograph is “like a microscope without lenses,” Buettner explains, so the image is reconstructed mathematically from the collected data, rather than physically by bending light beams using lenses. Lenses for X-rays exist, but they are very complex, and cost $40,000 to $50,000 apiece, he says.

    But an alternative way of reading the data may be possible, using an additional metal layer added to the other layers. By creating a particular texture on this added layer, it may be possible to detect differences in the layer’s electrical resistance depending on whether a skyrmion is present or not in the adjacent layer. “There’s no question it would work,” Buettner says, it’s just a matter of figuring out the needed engineering development. The team is pursuing this and other possible strategies to address the readout question.

    The team also included researchers at the Max Born Institute and the Institute of Optics and Atomic Physics, both in Berlin; the Institute for Laser Technologies in Medicine and Metrology at the University of Ulm, in Germany; and the Deutches Elektroniken-Syncrotron (DESY), in Hamburg. The work was supported by the U.S. Department of Energy and the German Science Foundation.

    See the full article here .

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  • richardmitnick 12:20 pm on August 5, 2016 Permalink | Reply
    Tags: , , Skyrmions, The future of data storage,   

    From Southampton: “Nanosize magnetic whirlpools could be the future of data storage” 

    U Southampton bloc

    University of Southampton

    3 August 2016
    No writer credit found

    1
    Skyrmions could be the future of data storage.

    The use of nanoscale magnetic whirlpools, known as magnetic skyrmions, to create novel and efficient ways to store data will be explored in a new £7M research programme involving University of Southampton researchers.

    Skyrmions, which are a new quantum mechanical state of matter, could be used to make our day-to-day gadgets, such as mobile phones and laptops, much smaller and cheaper whilst using less energy and generating less heat.

    It is hoped better and more in-depth knowledge of skyrmions could address society’s ever-increasing demands for processing and storing large amounts of data and improve current hard drive technology.

    Revolutionise data storage

    Scientists first predicted the existence of skyrmions in 1962 but they were only discovered experimentally in magnetic materials in 2009.

    The UK team, funded by the Engineering and Physical Sciences Research Council (EPSRC), now aims to make a step change in our understanding of skyrmions with the goal of producing a new type of demonstrator device in partnership with industry.

    Skyrmions, tiny swirling patterns in magnetic fields, can be created, manipulated and controlled in certain magnetic materials. Inside a skyrmion, magnetic moments point in different directions in a self-organised vortex. Skyrmions are only very weakly coupled to the underlying atoms in the material, and to each other, and their small size means they can be tightly packed together. Together with the strong forces that lock magnetic fields into the skyrmion pattern, the result is that the magnetic information encoded by skyrmions is very robust.

    Scientists can potentially move a skyrmion with 100,000 times less energy than is needed to move a ferromagnetic domain, the objects currently used in the memory of our computers and smartphones. Currently when we access information through the web, we remotely use hard disk drives that generate lots of heat and waste lots of energy. Skyrmionic technology could allow this to be done on smaller scale devices which would use much less energy.

    Skyrmions could therefore revolutionise the way we store data.

    Consortium of experts

    The Southampton researchers involved in the project are Professor Hans Fangohr and Dr Ondrej Hovorka from the University’s Computational Modelling Group. Professor Fangohr said: “Southampton will support this national grant into Skyrmion research by providing the computational science expertise and computational modelling to underpin, help understand and guide experimental work at our partner sites in Cambridge, Durham, Oxford and Warwick.

    “The skyrmions provide rich physics – this project will explore both the more fundamental physics questions that they raise and the potential for skyrmion use in applications.”

    The national consortium includes experts from the universities of Durham, Warwick, Oxford, Cambridge and Southampton, plus industry partners.

    World of opportunities

    The first prediction of a new type of stable configuration came from British physicist Tony Skyrme and has since opened up a whole variety of different sized and shaped skyrmion objects with different properties to conventional matter. However, numerous questions remain unanswered which focus on how best to exploit the unique magnetic properties of these magnetic excitations in devices.

    The three generic themes the team will look at are:

    • The development, discovery and growth of magnetic materials that host skyrmion spin textures;

    • A greater understanding of the physics of these objects;

    • Engineering of the materials to application.

    The research team will use state-of-the-art facilities such as synchrotron, neutron and muon sources both within the UK and internationally. The research is funded from summer 2016 until 2022.

    The research team is currently looking for five postdoctoral research associates to join the project. For more information about these opportunities, please visit http://www.skyrmions.co.uk

    More information about the Southampton post on computational modelling is available at http://www.southampton.ac.uk/~fangohr/vacancies/programmegrant.html

    See the full article here .

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