Inducing out-of-plane precession of magnetization for microwave-assisted magnetic recording with an oscillating polarizer in a spin-torque oscillator

The dynamics of a simple design of a spin-torque oscillator (STO) compatible with microwave-assisted magnetic recording were investigated. The STO with Ni₈₀Fe₂₀ (NiFe) used as a polarizer and Fe₆₇Co₃₃ (FeCo) used as a field generating layer was fabricated and measured. As the bias voltage increased, the magnetization reversal of NiFe occurred, then, multiple signals appeared in the power spectra. The signals reflected out-of-plane precession (OPP) mode oscillation of both the FeCo and NiFe layers, as well as the magnetoresistance effect of the STO, which had a frequency equal to the difference between the oscillation frequencies of the NiFe and FeCo layers. Such dynamics were reproduced by micromagnetic simulation. The results of the experiment and simulation demonstrate the merit of realizing OPP mode oscillation with a simple and thin structure suitable for a narrow gap recording head. In particular, the experimental results obtained with this STO design revealed that the cone angle for OPP mode oscillation of the FeCo layer (estimated by using the macrospin model) was large, namely, ∼ 70 °.