Direct determination of magnetic coupling across individual boundaries

Significance 

For the past few decades, studies involving magnetic coupling across the boundaries of magnetic materials have attracted significant interest amongst researchers. This can be attributed to the rapid increase in the demand for high-performance magnetic devices and materials. Unfortunately, due to the limitations of the current techniques, the interaction between the magnetic coupling of grain boundaries (GB) and local atomic structures together with their roles on the magnetic coupling has not been fully explored. Owing to the complex nature of the atomic structures of the GBs, it is difficult to determine their individual magnetic properties. Thus, a better understanding of the effects of the atomic structure of the GBs on the magnetic coupling across their interfaces is important for exploring and determining the magnetic behaviors and properties of magnetic materials.

In a recently published research, the atomic structure and magnetic properties of the GBs have been obtained simultaneously using scanning transmission electron microscopy (STEM) and differential phase contrast imaging (DPC). The information obtained has henceforth been used to investigate the interaction between them. For example, antiferromagnetic coupling boundary was predicted in magnetite (Fe3O4) using the first-principles calculations. However, no experimental studies have been done to support the theoretical findings.

Recently, researchers in Japan led by Professor Yuichi Ikuhara experimentally investigated the atomic structure and magnetic coupling of magnetite twin boundaries. Their main objective was to experimentally determine the magnetic coupling and properties across the magnetite twin boundaries, which could, in turn, be used as a supportive evidence to the initial theoretical predictions. Their research work is currently published in the research journal, ACS Nano.

The research team commenced their experimental work by reducing a single hematite crystal into a high magnetite phase in the presence of high temperatures. Thereafter, a high density of magnetite twins was prepared. Eventually, a combination of STEM, DPC and atomistic first-principles calculations were employed to determine the magnetic coupling across the twin boundaries and the effects of the various atomic core structures and electronic structures in the TBs.

The authors observed that the magnetic coupling across the magnetite twin boundaries can either be ferromagnetic or antiferromagnetic. Consequently, they realized that the magnetic coupling directly depended on the resultant electronic structure and the atomic core structure of the twin boundaries.

The experimental results provide a supportive evidence to the initially predicted results on the magnetic coupling of magnetite twin boundaries due to their consistency. Also, considering the excellent electronic and magnetic properties of the magnetite materials and the fact that they are readily available, the authors are optimistic that the study findings will significantly contribute to the in-depth understanding of the interaction relationship between the magnetic properties and local atomic structures of the individual GBs. As such, it will promote the development of more advanced and high-performance magnetic materials and devices.

Direct determination of magnetic coupling across individual boundaries, Advances in Engineering
Credit: ACS Nano, 12(3), 2662-2668. (2018).

Reference

Chen, C., Li, H., Seki, T., Yin, D., Sanchez-Santolino, G., Inoue, K., Shibata, N., Ikuhara, Y. (2018). Direct Determination of Atomic Structure and Magnetic Coupling of Magnetite Twin Boundaries.  ACS Nano, 12(3), 2662-2668.

Go To ACS Nano

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