Influence of dynamical dipolar coupling on spin-torque-induced excitations in a magnetic tunnel junction nanopillar

Spin-torque-induced excitations are numerically analyzed for an MgO-based magnetic tunnel junction nanopillar composed of a CoFe/Ru/CoFeB synthetic ferrimagnetic layer and a CoFeB layer. By performing macrospin simulations, we demonstrate that dynamical coupling between ferromagnetic layers through dipole-dipole interactions has a significant influence on the oscillation modes. In particular, we show that acoustic-like and optical-like oscillation modes established by the dynamical dipolar coupling emerge, depending on the in-plane bias field. The optical-like oscillation mode is stable under a wider current range than the acoustic-like one.