Influence of disorder on spin-orbit torques in perpendicularly magnetized FePt single layer

We report the disorder-dependent spin-orbit torques (SOT) in 3-nm-thick FePt single layer grown on MgO (001) substrate. With varying growth temperatures, perpendicularly magnetized FePt films with different ordering have been achieved. The magnetization can be almost completely switched for the films with enormous disorder, while very small percent of magnetization can be switched for the films with the mixture of fully L10 ordered and poor chemical ordering. Through harmonics measurements, we have found that the spin Hall angle is larger for the mixed ordered FePt film, indicating larger spin current generation efficiency. However, in this film, the complicated magnetization dynamics due to the mixture of fully L10 ordered and poor chemical ordering has impeded the magnetization switching. This finding illustrates the efficiency of SOT in FePt single layer is much dependent on the disorder.