Micromagnetic simulation on dynamics of spin transfer torque magnetization reversal

The detailed micromagnetic calculation results on the dynamics of spin transfer torque magnetization reversal is reported. Nano-pillars with CoFe/Ru/CoFe/Cu/CoFe film stacks are utilized with CoFe/Ru/CoFe trilayer as the strongly anti-ferromagnetic-coupled pinned layer. Magnetization reversal plots from anti-parallel (AP) to parallel (P) configuration with the nano-pillar shape ellipsoid and rectangular are determined. Results show that the threshold current for rectangular-shaped nano-pillars dramatically increases which is due to the pinning effect at the corners or the said pillars. In the case of magnetization reversal from P to AP configuration, the tendency is completely same. On the other hand, the simulation results indicate that the threshold current is not dependent on the aspect ratio of nano-pillars. Comparing the threshold currents for P to AP case between temperatures T=77 K and T=300 K, it is noted that the threshold current for the short pulse at T=77 K is smaller than that for T=300 K. This is also the same result for the AP to P case. These results suggest that a decrease in the coherent time of the precession movement of magnetization caused by the thermal scattering increases the time of spin transfer torque magnetization reversal.