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New Microscope Technique Unlocks Secrets of Magnetic Fields

A Japanese research team comprising scientists from Kyushu University, RIKEN, Hitachi, Ltd. (TSE 6501, Hitachi), and HREM Research Inc. (HREM) has made a significant advancement in the observation of magnetic fields at previously unthinkable small scales. The study has been published in the journal Nature.

New Microscope Technique Unlocks Secrets of Magnetic Fields
Thanks to advanced image acquisition and automated aberration correction techniques, researchers managed to measure magnetic fields in Ba2FeMoO6 at a groundbreaking resolution of 0.47 nm for a method that enables the observation of uneven samples. Such a high resolution is critical when observing magnetic phenomena that occur at the interface between materials. Image Credit: Toshiaki Tanigaki / Hitachi, Ltd.

In collaboration with the National Institute for Materials Science (NIMS) and the National Institute of Advanced Industrial Science and Technology (AIST), the team used Hitachi's atomic-resolution holography electron microscope—equipped with newly developed image acquisition technology and defocus correction algorithms—to visualize the magnetic fields of individual atomic layers within a crystalline solid.

Creating and using high-performance materials with specialized properties have enabled numerous advancements in electronic devices, catalysis, transportation, and energy production. Electron behavior and atom arrangement are among the most important elements that determine a crystalline material's characteristics.

The orientation and strength of magnetic fields precisely at the interface between atomic layers or different materials are particularly significant, and they frequently contribute to the explanation of a wide range of unusual physical phenomena.

Before this discovery, the highest resolution at which atomic layer magnetic fields could be seen was approximately 0.67 nm, a record Hitachi set in 2017 with its state-of-the-art holography electron microscope.

Now, thanks to a sizable collaborative project, researchers have succeeded in pushing this limit even further by addressing a few significant shortcomings in Hitachi's holography electron microscope.

The researchers greatly accelerated the imaging process. First, they created a system to automatically adjust and control the apparatus during data acquisition, producing 10,000 images in 8.5 hours. They then reduced noise in these images by applying particular averaging operations, yielding much clearer images with distinct magnetic and electric field data.

The correction for minute defocusing, which resulted in aberrations in the acquired images, was the next challenge to be tackled.

The idea of post-image-capture correction of aberrations we employed is exactly the same as that which had motivated Dr. Dennis Gabor to invent electron holography in 1948. In other words, the methodology was already theoretically established. Until now, however, there had been no technological implementations for such automated correction in off-axis electron holography.

Toshiaki Tanigaki, Chief Researcher, Hitachi, Ltd.

The employed technique could compensate for defocusing caused by small shifts in focus by analyzing reconstructed electron waves. This method produced images with no residual aberrations, allowing the magnetic field to distinguish atom positions and phases clearly.

The group utilized these two innovations to measure the electron holography of samples of Ba2FeMoO6, a layered crystalline material with distinct magnetic fields between adjacent atomic layers2FeMoO6, a layered crystalline material with distinct magnetic fields between adjacent atomic layers, by utilizing these two innovations.

They could observe the magnetic fields of Ba2FeMoO6 at an unprecedented resolution of 0.47 nm, surpassing the previous record.

This result opens doors to direct observations of the magnetic lattices in specific areas, such as interfaces and grain boundaries, in many materials and devices. Our study marks the first step towards investigating many veiled phenomena whose existence can be revealed by electron spin configurations in magnetic materials.

Toshiaki Tanigaki, Chief Researcher, Hitachi, Ltd.

The group hopes that their incredible accomplishment will aid in the resolution of numerous scientific and technological problems.

Our atomic-resolution holography electron microscope will be used by various parties, contributing to advances in a wide range of fields ranging from fundamental physics to next-generation devices. Ultimately, this would pave the way for the realization of a carbon-neutral society through the development of high-performance magnets and highly functional materials that are essential for decarbonization and energy-saving efforts,” concluded Tanigaki

Journal Reference:

Tanigaki, T., et al. (2024) Electron holography observation of individual ferrimagnetic lattice planes. Nature.

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