Effects of Fe Deficiency and Co Substitution in Polycrystalline and Single Crystals of Fe3GeTe2

Abstract

Fe3GeTe2 is a two-dimensional van der Waals material with a ferromagnetic ground state and a maximum transition temperature Tc ∼225 K. However, when Fe3GeTe2 is synthesized, lower values of Tc 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 Fe3GeTe2 grown by chemical vapor transport with ∼8% excess Fe in the starting materials display an optimum Fe content and magnetic transition temperature.