Tuning Magnetic Order in the van der Waals Metal Fe5GeTe2 by Cobalt Substitution

TL;DR

This study combines theoretical calculations and experiments to show how cobalt substitution in Fe5-xGeTe2 can tune its magnetic order and increase the Curie temperature, highlighting the importance of atomic arrangement and stacking.

Contribution

It demonstrates that cobalt substitution effectively manipulates magnetic properties and structural order in Fe5-xGeTe2, revealing the interplay between composition, structure, and magnetism.

Findings

Cobalt substitution up to 30% increases Curie temperature.

Approximately 50% cobalt induces antiferromagnetic order.

Structural change from rhombohedral to primitive cell with cobalt content.

Abstract

Fe5-xGeTe2 is a van der Waals material with one of the highest reported bulk Curie temperatures, $T_C$ ~ 310K. In this study, theoretical calculations and experiments are utilized to demonstrate that the magnetic ground state is highly sensitive to local atomic arrangements and the interlayer stacking. Cobalt substitution is found to be an effective way to manipulate the magnetic properties while also increasing the ordering temperature. In particular, cobalt substitution up to 30% enhances $T_C$ and changes the magnetic anisotropy, while approximately 50% cobalt substitution yields an antiferromagnetic state. Single crystal x-ray diffraction evidences a structural change upon increasing the cobalt concentration, with a rhombohedral cell observed in the parent material and a primitive cell observed for ~46% cobalt content relative to iron. First principles calculations demonstrate that it is a combination of high cobalt content and the concomitant change to primitive layer stacking that produces antiferromagnetic order. These results illustrate the sensitivity of magnetism in Fe5-xGeTe2 to composition and structure, and emphasize the important role of structural order/disorder and layer stacking in cleavable magnetic materials.