Visualization of the origin of magnetic forces by atomic resolution electron microscopy

Figure 1. Real-space magnetic field image of an antiferromagnetic α-Fe2O3 Atomic structure image (left) and corresponding magnetic field image (right). In the atomic structure image, Fe atoms are visualized as bright spots. In the magnetic field image, the color contrast indicates the direction and strength of the magnetic field. The inset color wheel shows how color and shade indicate the direction and strength of the magnetic field in the vector color map. Antiparallel magnetic fields on adjacent Fe atomic layers are clearly observed, visualizing the antiferromagnetic order in this crystal. 1 credit

The joint development team of Professor Shibata (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 made using the new Magnetic Fieldless Atomic Resolution STEM (MARS). 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 to electric fields, the technology to observe magnetic fields was unexplored. since the development of the electron. microscopes. This is a landmark achievement that will rewrite the history of microscope development.

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

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

Visualization of the origin of magnetic forces by atomic resolution electron microscopy

Figure 2. Atomic Resolution STEM without Developed Magnetic Field (MARS) A new magnetic object lens system is installed in this microscope. Combined with a higher-order aberration corrector, an electron beam can be focused onto a sample at the atomic scale, while maintaining the sample in a magnetic field-free state. 1 credit

From the current research results, the observation of the atomic magnetic field has been demonstrated, and a method for observing atomic magnetic fields has been established. This method is expected to become a new measurement method in the future which will lead to the research and development of various magnetic materials and devices such as magnets, steels, magnetic devices, magnetic memory, magnetic semiconductors, spintronics and topological materials.

Direct Atomic Resolution Imaging of Magnetic Materials

More information:
Yuji Kohno et al, Real-space visualization of the intrinsic magnetic fields of an antiferromagnet, Nature (2022). DOI: 10.1038/s41586-021-04254-z

Provided by Japan Science and Technology Agency

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