Micromagnetic simulation of critical current density of spin transfer torque switching in a full-Heusler Co₂FeAl_0.5Si _0.5 alloy spin valve nanopillar

We investigated the critical current density of spin transfer torque switching in a full-Heusler Co₂FeAl_0.5Si_0.5 alloy spin-valve nanopillar through micromagnetic simulations. The simulations explain the experimental results on the resistance versus external magnetic field and yield good agreement with the measured switching behavior. It is shown that different magnitudes of current densities and directions of external magnetic fields give rise to a shift of resistance hysteretic loop and a variable range of switching. We demonstrated that three critical current densities have different slopes with Gilbert damping constant α and spin polarization constant η, indicating that α and η have different contributions to the critical current densities. Furthermore, we found that the area of resistance-current hysteretic loop decreases as the nanopillar size decreases. The domain structures indicated that the magnetization reversals have different switching processes between small and large sizes of pillars.