Atomistic Model of Magnetic Tunnel Junction Spin-Torque Nano-Oscillators

We have developed a model of a CoFeB/MgO magnetic tunnel junction nano-pillar for application as a spin torque nano-oscillator (MTJ-STNO) using an atomistic model combined with a spin accumulation model. We investigate the effect of current density on magnetization dynamic states and the impact of the precession angle between magnetizations in the free layer and the pinned layer on the performance of the MTJ-STNO. An optimal current density is found where the relatively narrow linewidth within the simulation framework. Here, the magnetization rotates with a resonant frequency in the GHz range, reaching the steady precessional state within 1 ns. This behavior is caused by the balance between the Gilbert damping torque and the adiabatic spin torque in the free layer. The optimal current density decreases as the precession angle increases, because the spin torque acting on the magnetization in the free layer increases. As a result, the resonant frequency decreases (from 22.56 to 11.02 GHz) and power consumption decreases to the μW level, while the amplitude increases. This study is an important milestone toward the application of STNO for the next-generation data and communication technologies such as wireless communication, microwave assisted magnetic recording (MAMR), and neuromorphic computing.