Effect of process temperature on structure and magnetic properties of perpendicularly magnetized D0₂₂-Mn₃Ge thin films on a Cr buffer layer

We investigated the effect of post-annealing on the perpendicular magnetic anisotropy constant (K_u) and surface roughness (R_a) of Mn₃Ge thin films grown at comparatively low temperatures (room temperature, 150, 200, and 250 °C) on Cr buffer layers. The films grown at ≥ 200 °C exhibit a D0₂₂-ordered crystal structure in an as-deposited state. The post-annealing process demonstrates differences in trends between the 200-°C-grown film and the 250-°C-grown film. The 200-°C-grown film displays significant degradation of K_u and an increase in R_a upon annealing at >300 °C because of its poor thermal durability, while the 250-°C-grown film is still intact even at 500 °C. The 250-°C-grown film post-annealed at 300 °C displays relatively high K_u while R_a remains low. It may be possible to grow D0₂₂-Mn₃Ge with higher K_u and low R_a using a buffer-layer material with a lattice-matched crystal structure with D0₂₂-Mn₃Ge and higher thermal durability than Cr.