Micromagnetic Studies of Spin-Torque Oscillator Adjacent to Soft Magnetic Thin Film

We studied the precession frequency and the corresponding Fourier component intensity of a spin-torque oscillator (STO), when adjacent to a soft magnetic film or a magnetic recording write-pole tip, for a drive current range of 10-400 MA/cm 2 . The soft film interferes with the precession of the magnetic moment in the field-generation layer (FGL) of the STO, enhancing the critical current density required to drive a stable, high-frequency precession with a large in-plane component (working mode). Vibration of the magnetization in the soft film occurs when the FGL precesses nearby. A saturated pole tip can generate a large but inhomogeneous field in the STO, and the STO can achieve a working mode under a large driven current density of around 250 MA/cm 2 . However, the precession frequency is limited to below 14 GHz, which does not meet the optimum recording condition in microwave-assisted magnetic recording.