University of Tsukuba

Graduate School of Science, The University of Tokyo

Institute of Engineering Innovation

Outline

A topological insulator is a material that has the properties of a metal that conducts electricity on its surface while its crystal interior is an insulator. The surface of a topological insulator has a unique state in which spin-aligned electrons move at high speed without scattering, which is expected to be applied to super energy-saving devices. In this study, we have observed that the ferromagnetic property of iron "seeps out" to the SnTe side at the boundary between the topological crystal insulator SnTe (tin telluride) and familiar iron, resulting in a ferromagnetic state with aligned electron spins on the SnTe surface, as revealed by neutron observation (polarized neutron reflectometry) has revealed that the ferromagnetic properties of iron "seep" out to the SnTe surface.

This is the first observation of ferromagnetic staining in a topological crystal insulator, which is a relatively new type of topological insulator, and confirms that the electrons on the surface of a topological crystal insulator, which does not originally have magnetic properties, are given magnetic properties. In this study, the layers of iron, which is a magnet, and the topological crystal insulator were spatially separated, and it was confirmed that only the magnetic properties could be imparted to the topological surface, and that the ferromagnetism caused by this impregnation remained even at room temperature. This paves the way for the realization of novel physical properties such as quantum anomalous Hall effect and magnetic skyrmion at higher temperatures than ever before, and is expected to be applied to ultra-low power consumption devices and ultra-fine magnetic memory.

The research results were published in The Journal of Physical Chemistry Letters on August 29, 2022.

Figure: Schematic diagram of the junction of iron ( Fe) andSnTe and the magnetization distribution that occurs near the boundary surface. Depth dependence of the structure and magnetization distribution obtained from the reflection intensity when neutrons are reflected by nuclei in the crystal and by magnetic moments (magnetic properties) are shown. The measurement temperature is 2.4 K ( minus 271°C). The difference between the yellow and green curves (black curve) represents the ferromagnetic seepage into the interior of the SnTe layer, and the region with seepage is shown in red in the above figure. The arrows in the red region schematically show the magnitude of interfacial magnetization, indicating that ferromagnetism is seeping into the SnTe layer, which does not originally have magnetization.

Assistant Professor Ryota Akiyama and Professor Shuji Hasegawa of the Department of Physics participated in this research.

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