Effects of Fe deficiency and Co substitution in polycrystalline and single crystals of Fe$_{3}$GeTe$_{2}$

TL;DR

This study examines how iron deficiency and cobalt substitution influence the magnetic properties of Fe3GeTe2, revealing that Co reduces the transition temperature and that optimal Fe content enhances magnetic performance.

Contribution

It provides new insights into how Fe deficiency and Co substitution affect the magnetic transition temperature in Fe3GeTe2, with detailed synthesis and characterization.

Findings

Cobalt substitution significantly reduces the magnetic transition temperature.

Optimal Fe content in crystals enhances magnetic transition temperature.

Crystals grown by flux method achieve larger sizes with controlled Fe content.

Abstract

Fe$_{3}$GeTe$_{2}$ is a two-dimensional van der Waals material with a ferromagnetic ground state and a maximum transition temperature $T_{\mathrm{c}}\sim225$ K. However, when Fe$_{3}$GeTe$_{2}$ is synthesized lower values of $T_{\mathrm{c}}$ are often reported. This is attributed to a deficiency in the Fe at the 2c site in the crystal structure. Here we investigate the effect of Fe deficiency and the substitution of Co for Fe on the magnetic properties of this system. We have synthesized both polycrystalline material and single crystals by chemical vapor transport and the flux method, with the largest crystals obtained using the flux method. Cobalt substitution at the Fe site is found to significantly reduce the magnetic transition temperature. Crystals of Fe$_{3}$GeTe$_{2}$ grown by chemical vapor transport with $\sim 8\%$ excess Fe in the starting materials display an optimum Fe content and magnetic transition temperature.