Perpendicular magnetic anisotropy exhibited by two-dimensional layered materials improved by applying pressure

Because of their various attractive properties, such as high conductivity, flexibility, and transparency, two-dimensional layered materials have been proposed for various applications and have attracted significant attention, especially as new materials for next-generation electronics. Recently, materials exhibiting ferromagnetism have been discovered, and they are expected to be used as two-dimensional magnets in magnetic recordings and spintronics. In particular, the recently discovered Fe₃GaTe₂ maintains its magnetism at room temperature, and its magnetic orientation tends to be perpendicular to the plane (perpendicular magnetic anisotropy), making it a promising candidate for use in spin memory and thermoelectric devices. However, due to the insufficient strength of its perpendicular magnetic anisotropy at room temperature, the magnetic orientation cannot be kept perpendicular without the application of a magnetic field.

A research group comprising Graduate Student Riku Iimori of the Graduate School of Science at Kyushu University, and Professor Takashi Kimura of the Faculty of Science at the same university, was the world's first to reveal that applying pressure to this two-dimensional, layered magnet considerably improves perpendicular magnetic anisotropy. The results of their findings were published in the online edition of Communications Materials.

In this study, a fine, thin film of Fe₃GaTe₂, a two-dimensional magnet at room temperature, was transferred onto an insulating substrate, and then multiple fine electrodes were attached using various microfabrication techniques to create a device that can evaluate the magnitude of perpendicular magnetic anisotropy by measuring the Hall effect. Furthermore, the fabricated device was placed inside a pressure cell developed by the researchers, and the change in perpendicular magnetic anisotropy under an applied pressure was investigated.

Result shows that by applying a pressure of approximately 0.2 GPa to the Fe₃GaTe₂ thin film, the magnetization direction is maintained perpendicular even when no magnetic field is applied, and an increase in the applied pressure further increases perpendicular magnetic anisotropy. Additionally, the temperature at which the magnetic properties can be maintained (Curie point) does not change even when pressure is applied. These results indicate that the ferromagnetic properties are primarily governed by covalent bonding in the two-dimensional plane, while perpendicular magnetic anisotropy is mainly determined by van der Waals interlayer coupling. Various property improvements are required for the practical application of two-dimensional material devices. Numerous enhancements such as composition modulation and substrate optimization have been made so far.

In this study, the researchers find that the magnetic properties of a two-dimensional, layered magnetic material can be greatly improved simply by applying a relatively small pressure of approximately 0.2 GPa. This result indicates that applying pressure can effectively modulate the interlayer distance (gap between layers) due to van der Waals coupling and is expected to be an effective method for controlling various properties of two-dimensional materials and improving their characteristics.

Kimura said, "This result is attributed to the existence of gaps unique to two-dimensional layered materials, a phenomenon that cannot occur in conventional metals or insulators. If a device-mounting technology that allows pressure application and a technology that enables the manufacture and mass production of large-area thin films of this material can be established, we expect that this will dramatically improve the energy efficiency of various spin devices, making a major contribution to the digital society in the future."

Journal Information
Publication: Communications Materials
Title: Substantial enhancement of perpendicular magnetic anisotropy in van der Waals ferromagnetic Fe₃GaTe₂ film due to pressure application
DOI: 10.1038/s43246-024-00665-3