Anomalous impact of thermal fluctuations on spin transfer torque induced ferrimagnetic switching

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The dynamics of a spin torque-driven ferrimagnetic (FiM) system is investigated using the two-sublattice macrospin model. We demonstrate ultrafast switching in the picosecond range. However, we find that the excessive current leads to magnetic oscillation. Therefore, faster switching cannot be achieved by unlimitedly increasing the current. By systematically studying the impact of thermal fluctuations, we find that the dynamics of FiMs can also be distinguished into the precessional region, the thermally activated region, and the crossover region. However, in the precessional region, there is a significant deviation between FiM and ferromagnet (FM), i.e., the FM is insensitive to thermal fluctuations since its switching is only determined by the amount of net charge. In contrast, we find that the thermal effect is pronounced even when a very short current pulse is applied to the FiM. We attribute this anomalous effect to the complex relation between the anisotropy and overdrive current. By controlling the magnetic anisotropy, we demonstrate that the FiM can also be configured to be insensitive to thermal fluctuations. This controllable thermal property makes the FiM promising in many emerging applications such as the implementation of tunable activation functions in the neuromorphic computing.