Self-intercalation as origin of high-temperature ferromagnetism in epitaxially grown Fe5GeTe2 thin films

TL;DR

This study demonstrates that self-intercalation of Fe atoms in Fe5GeTe2 thin films significantly raises their magnetic ordering temperature, achieving ferromagnetism up to 375 K, which is promising for high-temperature spintronic applications.

Contribution

It reveals that self-intercalation during epitaxial growth enhances magnetic properties of Fe5GeTe2 by increasing exchange interactions, a novel approach for tuning 2D ferromagnetism.

Findings

Ferromagnetic order observed up to 375 K in epitaxial Fe5GeTe2 films.

Self-intercalated Fe atoms increase exchange interactions between layers.

X-ray and first-principles calculations confirm the role of intercalated Fe in magnetic enhancement.

Abstract

The role of self-intercalation in 2D van der Waals materials is key to the understanding of many of their properties. Here we show that the magnetic ordering temperature of thin films of the 2D ferromagnet Fe5GeTe2 is substantially increased by self-intercalated Fe that resides in the van der Waals gaps. The epitaxial films were prepared by molecular beam epitaxy and their magnetic properties explored by element-specific x-ray magnetic circular dichroism that showed ferromagnetic ordering up to 375 K. Both surface and bulk sensitive x-ray absorption modes were used to confirm that the magnetic signal is of an intrinsic nature. Fe occupation within the van der Waals gap was determined by x-ray diffraction which showed a notably higher occupation with respect to bulk crystals. We thus infer, supported by first-principles calculations, that the higher magnetic ordering temperature results from an increased exchange interaction between the individual Fe5GeTe2 layers mediated by Fe atoms residing within the van der Waals gaps. Our findings establish self-intercalation during epitaxial growth as an efficient mechanism to achieve high-temperature magnetism in a broad class of van der Waals materials.