Temperature (-23 Deg Celcius) Fig. :Magnetic structure observed by Lorentz transmission electron microscopy. (a) Helical stripe structure in the zero magnetic field. Dotted lines show the crystal grain boundary. (b) Skymrion crystal formed by applying a 150mT magnetic field perpendicular to the device. (c) Enlarged diagram of the skyrmion crystal. (d) Distribution of magnetization in a single skyrmion. Colors and arrows show the direction of electron spin in the skyrmion.

Driving an Electron Spin Vortex “Skyrmion” with a
Microcurrent

Large Advance toward Realization of Technology for Manipulation of
Magnetic Information with Low Current Density 1/100,000th that of
Conventional Technology

RIKEN, the University of Tokyo, and NIMS succeeded in forming a
skyrmion crystal, in which electron spin is aligned in a vortex
shape, in a microdevice using the helimagnet FeGe, and driving the
skyrmion crystal with an ultra-low current density less than
1/100,000 that of the current necessary to drive magnetic domain
walls in ferromagnets.

As a result of this research, it was possible to obtain guidelines
for the realization of a technology for manipulating the states of
magnetic information media with extremely low power
consumption.

This research result was achieved by a team headed by Dr. Xuizhen
Yu, a Postdoctoral Researcher in the Strong-Correlation Physics
Research Team of the Correlated Electron Research Group of the
RIKEN Advanced Science Institute, Group Director Prof. Yoshinori
Tokura of the University of Tokyo Graduate School of Engineering,
and Dr. Koji Kimoto, Unit Director of the Surface Physics and
Structure Unit, Advanced Key Technologies Division of NIMS.

Magnetic memory devices that use the direction of electron spin,
which is the source of magnetism, as digital information have
attracted attention as devices with the important features of high
speed and non-volatility, etc. In recent years, numerous attempts
have been made to manipulate that magnetic information electrically
without utilizing a magnetic field. If a current is passed through
a ferromagnet, it is possible to move the magnetic domain walls,
which are the boundaries between domains where magnetization is
upward-oriented and domains with downward orientation (at domain
walls, the direction of magnetic spin gradually changes).
Therefore, reversal of magnetization becomes possible and
information can be written. However, in order to drive the domain
walls in this manner, a large current density of at least
approximately 105 A/cm2 was necessary. Because this causes large
energy loss, in other words, large energy consumption, a method of
manipulating magnetic information media with a smaller current
density had been desired.

The research team investigated various functional magnetic
materials, and in 2010, succeeded in forming and observing a
skyrmion crystal by applying a weak magnetic field of less than 200
millitesla (mT) to a thin slice of the helimagnet FeGe at near room
temperature. In the present research, the team fabricated
microdevices with a length of 165μm, width of 100μm, and
thicknesses of 100nm to 30μm using the same FeGe. When a
magnetic field of approximately 150mT at temperatures from
-23°C to near-room temperature (-3°C) was applied, skymrion
crystals in which a stable skyrmion with a diameter of about 70nm
was aligned in a triangular lattice shape were observed. The team
succeeded in driving the skymrion crystal with an ultra-low current
density (the minimum density is approximately 5A/cm2), which is
less than 1/100,000th that required to drive magnetic domain walls
in conventional ferromagnets. The fact that the skymrion can be
driven with this extremely low current density represents the first
step toward the development of low power consumption magnetic
memory devices using skymrions as an information medium. Various
applications can also be expected in the field of spintronics,
which is currently an area of active research as a next-generation
electronic technology.

The main portion of the research result was achieved in the
“Quantum Science on Strong Correlation” project (Core
Researcher: Yoshinori Tokura) of the Funding Program for
World-Leading Innovative R&D on Science and Technology (FIRST)
of the Japan Society for the Promotion of Science (JSPS), with
system design by the Council for Science and Technology Policy, and
was supported by the JSPS. Part of the research was also supported
by the Strategic Basic Research Programs/ERATO (Exploratory
Research for Advanced Technology) Type Research Projects of the
Japan Science and Technology Agency (JST) and the Nanotechnology
Network of Japan’s Ministry of Education, Culture, Sports,
Science and Technology (MEXT), and has been published in the online
edition of the British science journal “Nature
Communications” on August 7 (August 8 Japan time).

For more detail

Dr. Xiuzhen Yu

Strong-Correlation Physics Research Team,

Correlated Electron Research Group,

Advanced Science Institute, RIKEN

TEL: +81-48-462-1111(ext. 6324)

FAX: +81-48-462-4703

Prof. Yoshinori Tokura

Team Leader, Strong-Correlation Physics Research Team,

Group Director, Correlated Electron Research Group,

Advanced Science Institute, RIKEN

TEL:+81-3-5841-6870

FAX:+81-3-5841-6839

For more detail about “Quantum Science on Strong
Correlation” project

Dr. Izumi Hirabayashi

Deputy Group Director, Correlated Electron Research Group, Advanced
Science Institute,

Team Leader, Strong-Correlation Research Support Team, Correlated
Electron Research Group, Advanced Science Institute, RIKEN

TEL: +81-48-462-4660

FAX: +81-48-462-1687

For general inquiry

RIKEN Public Relations Office

TEL:+81-48-462-9272

FAX:+81-48-462-4715