Layer dependence of anisotropy field and Curie temperature of 2D ferromagnets: Fe₅Ge₂Te₂, Fe₃GeTe₂

Layered ferromagnets, a subset of the van der Waals family, exhibit many fascinating properties that have attracted a great deal of attention in the condensed matter physics community. Fe₅Ge₂Te₂ (FG2T) and Fe₃GeTe₂ (FGT) stand out among others due to their unusually strong magnetic anisotropy perpendicular to the atomic layers, metallicity, and high Curie temperatures. We have fabricated FG2T and FGT nanodevices with a range of thicknesses down to monolayers by exfoliating flakes from crystals grown by solid-state reaction. We protect the thin flakes by depositing a thin Al₂O₃ film. Our transport measurements indicate that the Al₂O₃ protected devices are stable. By performing transport measurements at different temperatures with the external field oriented in-plane and out-of-plane, we obtain the longitudinal resistivity, anomalous Hall resistivity, Curie temperature, coercive field, as well as saturation field for all devices. We find the anomalous Hall conductivity is proportional to the number of layers and it is higher for FG2T than FGT. While the Curie temperature in FG2T is higher than that in FGT, the anisotropy field of the former is smaller.

This work was supported by NSF/ECCS No. 2051450.