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

Abstract

We investigated the effect of post-annealing on the perpendicular magnetic anisotropy constant (Ku) and surface roughness (Ra) 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 Ku and an increase in Ra 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 Ku while Ra remains low. It may be possible to grow D022-Mn3Ge with higher Ku and low Ra using a buffer-layer material with a lattice-matched crystal structure with D022-Mn3Ge and higher thermal durability than Cr.