Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Phenomenon in Nanodisk Magnetic Vortices

09.08.2012
Berkeley Lab Researchers Take a Mesocale Look at Magnetic Vortex Formations

The phenomenon in ferromagnetic nanodisks of magnetic vortices – hurricanes of magnetism only a few atoms across – has generated intense interest in the high-tech community because of the potential application of these vortices in non-volatile Random Access Memory (RAM) data storage systems.


MTXM images of in-plane (a) and out-of-plane (b) magnetic components in an array of permalloy nanodisks. In-plane magnetic rotation is shown by white arrow (a). Core polarization is marked by black (up) and white (down) spots. Image (c) shows the complete vortex configuration of each nanodisk in the array. (Images courtesy of Im and Fischer)

New findings from scientists at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) indicate that the road to magnetic vortex RAM might be more difficult to navigate than previously supposed, but there might be unexpected rewards as well.

In an experiment made possible by the unique X-ray beams at Berkeley Lab’s Advanced Light Source (ALS), a team of researchers led by Peter Fischer and Mi-Young Im of the Center for X-Ray Optics (CXRO), in collaboration with scientists in Japan, discovered that contrary to what was previously believed, the formation of magnetic vortices in ferromagnetic nanodisks is an asymmetric phenomenon. It is possible that this breaking of symmetry would lead to failure in a data storage device during its initialization process.

“Our experimental demonstration that the vortex state in a single magnetic nanodisk experiences symmetry breaking during formation means that for data storage purposes, there would probably need to be a lengthy verification process to correct for errors,” Im says. “On the plus side, non-symmetric behavior creates a biasing effect that could be applied to a sensor or a logic device.”

“Our study is also a nice example of mesoscale science, which brings the nanoscience of the last decade to the next level,” Fischer says. “Mesoscale phenomena encompass complexity and functionality over various length scales.”

Im and Fischer describe this study in a paper published in the journal Nature Communications. The paper is titled “Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk.” Co-authoring this paper were Keisuke Yamada, Tomonori Sato, Shinya Kasai, Yoshinobu Nakatani and Teruo Ono.

Magnetic vortex states are generated in ferromagnetic nanodisks because the spin of electrons, which gives rise to magnetic moments, must follow the shape of the disk to ensure closure of magnetic flux lines. This results in the curling of the in-plane magnetization flux lines. At the center of these curling flux lines is a needlelike core, an “eye-of-the-hurricane” that points either up or down with respect to the surface plane of the nanodisk.

“The magnetization of the ferromagnetic nanodisk therefore has two components, the up or down polarity of the core and the chirality (rotation) of the in-plane magnetization, which can be either clockwise or counter-clockwise,” Im says. “It has been proposed that these four independent orientations can be used to store binary data in novel non-volatile storage devices.”

“The assumption has been that magnetic vortex states would exhibit a perfect symmetry required for vortex-based data-storage devices because the energy states of the four orientations were equivalent, meaning four logical values per unit,” Fischer says. “However, we show that if you analyze a sufficiently large ensemble of nanodisks, this is not the case. Our results demonstrate how mesoscale behavior can be significantly different from nanoscale behavior.”

The key to the discovery of magnetic vortex symmetry-breaking was the research team’s ability to simultaneously observe both chirality and polarity in a large array of nanodisks. Previous studies focused on either the chirality or polarity in a single disk. This simultaneous observation was accomplished using the XM-1 x-ray microscope at ALS beamline 6.1.2. XM-1 provides full-field magnetic transmission soft X-ray microscopy with spatial resolution down to 20 nanometers, thanks in part to the high quality X-ray optics provided by CXRO researchers.

“Magnetic transmission soft X-ray microscopy offers high spatial and temporal resolution imaging with element specific magnetic contrast, making it an ideal method for studying nanoscale spin dynamics, such as vortex core dynamics,” Im says. “XM-1 provides a large field of view and therefore very short exposure times per disk.”

Im, Fischer and their colleagues fashioned nanodisks from permalloy, a nickel and iron alloy whose magnetic properties have been fully characterized. Using electron-beam lithography they patterned large arrays of disks, each with a radius of 500 nanometers and a thickness of 100 nanometers. The arrays were deposited on silicon-nitride membranes to allow for sufficient transmission of soft X-rays and exposed in XM-1 for a few seconds. In their paper, the authors conclude that the observed symmetry breaking most likely results from a combination of intrinsic and extrinsic factors. The intrinsic factor is believed to be an antisymmetric coupling between the spins of two electrons called the Dzyaloshinskii–Moriya interaction. Extrinsic factors include defects along the edges of the nanodisks and rough nanodisk surfaces.

“Our finding is certainly a new physical phenomenon in magnetic vortices, which has not been explored so far,” says Im. “The statistical significance of our experimental work and our rigorous 3D micromagnetic simulation for the generation process of vortex state provides important new information for the less known physics in the magnetization process of nanodisks.”

“We’ve also shown that deterministic behavior and functionality on the mesoscale cannot always be extrapolated from even a complete understanding of nanoscale behavior,” Fischer says. “In other words, understanding a single LEGO brick might not be enough to build a large and complex structure.”

Im is the corresponding author of the Nature Communications paper. Co-authors Yamada and Ono are with Kyoto University, co-authors Sato and Nakatani are with the University of Electro-Communications at Chofu, and co-author Kasai is with Japan’s and National Institute for Materials Science.

This research was supported by the DOE Office of Science.

Lawrence Berkeley National Laboratory (Berkeley Lab) addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

Lynn Yarris | EurekAlert!
Further information:
http://www.lbl.gov

More articles from Physics and Astronomy:

nachricht First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>