Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering

We report the enhancement of spin-orbit torques (SOT) in MnAl/Ta films with improving chemical ordering through annealing. The switching current density is increased due to enhanced saturation magnetization MS and effective anisotropy field HK after annealing. Using harmonic measurements, we have found that both dampling-like effective field HD and field-like effective field HF were increased in the temperature range of 50 to 300 K, and the annealing has also enhanced the value of the spin Hall angle. The improved chemical ordering is considered to have enhanced the interfacial spin transparency and the transmitting of the spin current in the MnAl layer. The results suggest that MnAl films with high bulk perpendicular magnetic anisotropy are ideal for a systematic examination of SOT, in which the related magnetic and transport behaviors can be controllably varied with thermally tuned chemical ordering.