Visualization of the origin of magnetic forces by atomic resolution
electron microscopy
Accelerating research and development on state-of-the-art materials such
as magnets, semiconductors and quantum technology

Date:
February 24, 2022
Source:
Japan Science and Technology Agency
Summary:
Scientists have observed atomic magnetic fields, the origin
of magnetic forces, for the first time using an innovative
Magnetic-field-free Atomic-Resolution STEM they developed.



FULL STORY ==========================================================================
The joint development team of Professor Shibata (the University of Tokyo),
JEOL Ltd. and Monash University succeeded in directly observing an atomic magnetic field, the origin of magnets (magnetic force), for the first
time in the world.

The observation was conducted using the newly developed
Magnetic-field-free Atomic-Resolution STEM (MARS) (1). This team had
already succeeded in observing the electric field inside atoms for the
first time in 2012. However, since the magnetic fields in atoms are
extremely weak compared with electric fields, the technology to observe
the magnetic fields had been unexplored since the development of electron microscopes. This is an epoch-making achievement that will rewrite the
history of microscope development.


========================================================================== Electron microscopes have the highest spatial resolution among all
currently used microscopes. However, in order to achieve ultra-high
resolution so that atoms can be observed directly, we have to
observe the sample by placing it in an extremely strong lens magnetic
field. Therefore, atomic observation of magnetic materials that are
strongly affected by the lens magnetic field such as magnets and steels
had been impossible for many years. For this difficult problem, the
team succeeded in developing a lens that has a completely new structure
in 2019. Using this new lens, the team realized atomic observation of
magnetic materials, which is not affected by the lens magnetic field. The team's next goal was to observe the magnetic fields of atoms, which are
the origin of magnets (magnetic force), and they continued technological development to achieve the goal.

This time, the joint development team took on the challenge of observing
the magnetic fields of iron (Fe) atoms in a hematite crystal (a-Fe2O3) by loading MARS with a newly developed high-sensitivity high-speed detector,
and further using computer image processing technology. To observe
the magnetic fields, they used the Differential Phase Contrast (DPC)
method (2) at atomic resolution, which is an ultrahigh-resolution local electromagnetic field measurement method using a scanning transmission
electron microscope (STEM) (3), developed by Professor Shibata et al. The results directly demonstrated that iron atoms themselves are small magnets (atomic magnet). The results also clarified the origin of magnetism (antiferromagnetism (4)) exhibited by hematite at the atomic level.

From the present research results, the observation on atomic magnetic
field was demonstrated, and a method for observation of atomic
magnetic fields was established. This method is expected to become
a new measuring method in the future that will lead the research and development of various magnetic materials and devices such as magnets,
steels, magnetic devices, magnetic memory, magnetic semiconductors,
spintronics and topological materials.

This research was conducted by the joint development team of Professor
Naoya Shibata (Director of the Institute of Engineering Innovation,
School of Engineering, the University of Tokyo) and Dr. Yuji Kohno et
al. (Specialists of JEOL Ltd.) in collaboration with Monash University, Australia, under the Advanced Measurement and Analysis Systems Development (SENTAN), Japan Science and Technology Agency (JST).

Terms (1) Magnetic-field-free Atomic-Resolution STEM (MARS)


==========================================================================
An electron microscope is an instrument to directly observe the
microstructure in a sample, where an electron beam is injected into the
sample, and the electron beams transmitted and scattered by the sample
are magnified using a magnetic field lens. Currently, it is possible
to directly observe atoms using an electron microscope. In an optical microscope, the spatial resolution is in principle limited to about one micrometer due to the light source (visible light). On the other hand,
electron microscope is an instrument where this spatial resolution limit
is exceeded by utilizing the wave nature of electrons.

Therefore, it can be said that an electron microscope is an observation technology that applies the benefits of quantum mechanics in the most
direct way. The Magnetic-field-free Atomic-Resolution STEM (MARS) is an electron microscope developed by the present joint development team in
2019, capable of measuring a sample in a magnetic-field free environment.

(2) Differential Phase Contrast (DPC) method A method to measure the electromagnetic field at each point in a sample.

Specifically, when an electron beam is injected in a sample, the force of
the electromagnetic field that exists within the sample causes a slight trajectory change in the electron beam incident, and by measuring the difference in the electron beam intensity detected in each position of
a split detector, the electromagnetic field can be measured. Since the
spatial resolution of this method is basically determined by the size
of the electron probe, observation of an electromagnetic field at atomic resolution is in principle possible using the DPC method.

(3) Scanning Transmission Electron Microscope (STEM) An instrument
to directly observe the structure inside a sample. Specifically, a micro-focused electron beam is scanned on the sample, and observation
is conducted by measuring the intensity of electrons transmitted and
scattered by the sample. Currently, we can directly observe atoms using
a STEM.

(4) Antiferromagnetism A magnetism where spins of neighboring atoms are
aligned with each other facing antiparallel, and the material does not
have spontaneous magnetization as a whole.

========================================================================== Story Source: Materials provided by
Japan_Science_and_Technology_Agency. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Yuji Kohno, Takehito Seki, Scott D. Findlay, Yuichi Ikuhara, Naoya
Shibata. Real-space visualization of intrinsic magnetic fields
of an antiferromagnet. Nature, 2022; 602 (7896): 234 DOI:
10.1038/s41586-021- 04254-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220224112633.htm

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