Spin Transfer Torque Oscillation in Orthogonal Magnetization Disks

We numerically demonstrated the spin transfer torque oscillation (STO) in a magnetic orthogonal configuration by introducing a 90° magnetic coupling. In our model, the multilayer consists of a top layer with in-plane magnetic anisotropy, a nonmagnetic spacer, and a bottom layer with perpendicular magnetic anisotropy. The advantage of utilizing the orthogonal configuration is the high efficiency of spin transfer torque but it is difficult to stabilize STO. By introducing 90° magnetic coupling into the trilayer of FePt/spacer/Co
₉₀
Fe
₁₀
, or Ni
₈₀
Fe
₂₀
or Ni, a stable STO in an orthogonal configuration was realized. When the top layer was Ni with low levels of saturation magnetization, a small damping constant, and a small anisotropy, it exhibited high frequency and low amplitude. This indicates the possibility of controlling the STO frequency. Moreover, the STO frequency was increased by enhancing the 90° coupling. The combination of the orthogonal magnetization structure and 90° magnetic coupling is an effective approach to obtain a stable spin transfer torque oscillator with high frequency.