World's first observation of magnetic fields of individual lattice planes

This was achieved by using Hitachi's atomic-resolution holography electron microscope and a method enabling magnetic field observation of samples with uneven structures and compositions (hereinafter referred to as non-uniform samples) such as magnetic multilayer films, which have been difficult to observe so far, in collaboration with National Institute of Advanced Industrial Science and Technology (AIST) and National Institute for Materials Science (NIMS).

Observation was accomplished by developing a technology with a higher degree of electron-holography precision and automated post-image-capture focus correction. With this, it is now possible to observe magnetic fields of the atomic-layer level at local boundaries between materials (interfaces), which greatly affects the physical characteristics of materials that include non-uniform samples and characteristics of electronic devices. In the future, we will contribute to the advancement of fundamental science by elucidating magnetic phenomena occurring at the atomic-layer level and realisation of a carbon-neutral society through the development of high-performance magnets and highly functional materials used in electrification for decarbonisation as well as energy-saving devices for reducing total energy usage required in our daily life.

The research results have been published online in Nature, an international scientific journal, on July 4, 2024.

Electronic devices and motors are used in a variety of applications, including mobile phones, personal computers, cars, trains, and power plants, supporting our daily life. Many of those functions and performances are determined by the arrangement of atoms, which are the smallest unit of ordinary matter that forms material, and the behaviour of electrons. As such, to develop new functions and improve performance, there was a need for a technology enabling the ultra-high-resolution observation of matter at an atomic level. Since 1966, Hitachi has been developing the holography electron microscope as an instrument for the direct observation of electric and magnetic fields in extremely small regions, and in 2014, developed an atomic-resolution holography electron microscope with the support of the FIRST program (Figure 2). In 2017, Hitachi and RIKEN achieved a resolution of less than 1 nm, which enables magnetic-field observation of a few atomic layers. To achieve an even higher resolution, however, there were problems regarding improvement of microscope precision and correction of minute defocusing that occurs when images are captured.

Now, the collaborative research team solved these problems and developed a technology for realising magnetic field observation of individual lattice planes for non-uniform samples such as magnetic multilayer films, which have been difficult to observe so far.

The main features of the developed technology

1. Technology for automated acquisition of large quantities of images for improving precision in electron holography

The precision of electron holography is increased by increasing the number of acquired image data. A technology for automated acquisition of more than 10,000 images over about 8.5 hours while sustaining ultra-high-resolution has been developed by adding automated control and tuning of the microscope during data acquisition and speeding up the imaging based on technology developed in 2017 for precisely separating electric field data and magnetic field data from the result of electron holography observation.

2. Technology for digital aberration correction that automatically corrects minute defocusing

To obtain high resolution, a technology to correct minute defocusing that remains in observed data is required. The idea of post-image-capture correction of aberrations is exactly the same as that which motivated Dr. Dennis Gabor to invent electron holography in 1948, and it is theoretically established. To date, however, there has been no technology for automated correction. In this research, automated correction was successfully performed by developing an original algorithm that reduced the impact of noises contained in the experimental data by applying the technique, which corrected defocusing by analysing electron waves reconstructed from a focus series, to the electron holography.

The developed technology was applied to the atomic-resolution holography electron microscope to observe magnetic materials (Ba2FeMoO6) with magnetic fields of different strength and directions in each atomic layer, and was used to successfully observe magnetic fields of individual lattice planes in the material at the resolution of 0.47 nm, which upon comparing the experimental results with the simulation results was concluded to be the highest in the world for a method that enables observation of uneven samples.

Using this technology, detailed observation of the relationship between interface structures and magnetic fields in devices and materials has become possible, and the development of highly functional materials and energy-saving devices to realise a carbon-neutral society is expected to accelerate. Furthermore, supported by the Project for Promoting Public Utilisation of Advanced Research Infrastructure of the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT), the atomic-resolution holography electron microscope will be used by various parties to contribute to the advancement of science and technology in a wide range of fields from fundamental physics to advanced devices.