The first direct observation of an unusual magnetic
structure could lead to novel electronic and magnetic memory
devices
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| The structure of a skyrmion. Its atomic magnetic moments start
to point inwards under an externally applied magnetic field. |
| Copyright : Reproduced from Ref. 1 © 2010 X.Z. Yu et
al. |
In conventional ferromagnets, the individual magnetic moments of
the atoms that together comprise the magnetism of the material are
all aligned parallel, pointing in a common direction. In some
magnets, quantum-mechanical interactions between the electrons of a
material or the presence of internal electric fields, for example,
mean that the magnetic arrangements are more complex. Now, a rare
arrangement of magnetic moments, so-called skyrmions, has been
directly imaged by a team led by Yoshinori Tokura of the RIKEN
Advanced Science Institute, Wako. Tokura and his colleagues from
RIKEN and other research institutes in Japan and Korea confirmed
that skyrmions are very stable and that their manipulation could
form the basis for novel magnetic memories or electronic
devices1.
A skyrmion can be envisaged as a vortex-like arrangement of
magnetic moments that, towards the center of the structure,
increasingly twist and bend in downwards direction. In earlier
experiments by other research groups, the existence of skyrmions
had been inferred indirectly but efforts to image them, and to
confirm their structure, failed owing to their small size with
diameters of around 90 nanometers.
Tokura and his team accomplished their direct observation of
skyrmions by using a Lorentz transmission electron microscope,
which is suited to image magnetic structures at very high
resolution. Previously, physicists considered this type of
experiment impossible because observing skyrmions would require the
application of external magnetic fields that they thought would
disturb the imaging process of the microscope. The team realized,
however, that this problem could be overcome by applying the
external magnetic fields perpendicular to the imaging lens of the
microscope. Tokura says that this led to the breakthrough that
allowed them to show the emergence of skyrmions
unambiguously.
In addition to observing the expected periodic arrangement of many
skyrmions, the researchers were able to observe isolated skyrmions
and establish that they are also stable entities. The manipulation
of individual skyrmions could find application in novel magnetic
memories or in electronic devices, Tokura notes.
Realization of such applications, however, still requires
substantial work. Thus far, skyrmions have been observed only at
temperatures of around 40 Kelvin. “In future, we not only
need to find new materials where skyrmions are stable at room
temperature, but also find ways to manipulate their motion through
electromagnetic effects,” explains Tokura. He says that a
number of known oxide magnetic materials could fulfill these
criteria and may eventually lead to skyrmion-based devices.
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| An overhead view of skyrmions observed directly using a Lorentz
transmission electron microscope. |
| Copyright : Reproduced from Ref. 1 © 2010 X.Z. Yu et
al. |
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Journal information
1. 1.Yu, X. Z., Onose, Y., Kanazawa, N., Park, J, H., Han, J.
H., Matsui, Y., Nagaosa, N. & Tokura, Y. Real-space observation
of a two-dimensional skyrmion crystal. Nature 465, 901-904
(2010).
SOURCE
