Stability of Spin Torque Oscillators for MAMR: Perspectives of Materials and Design

Stability and reliability are two main concerns for the spin torque oscillator (STO) being used as a microwave generator in the microwave-assisted magnetic recording. Using micromagnetic simulation, we investigated the STO stability against the head gap field and the stray field from the recording media as a function of STO reference-layer properties. It is found that the K
_u
of the reference layer, the gap field, and the media stray field have great effects on the STO stability. In addition, we addressed the key issues of STOs under high current which are required for generating high enough oscillation frequency for effective writing, including high-current induced STO instability and thermally agitated disturbance on STO. The results show that the damping constant of the field generation layer (FGL) of STO not only plays a key role in reducing the driving current but also is a deterministic parameter on the enhancement of STO stability. Possible approaches to enhancing STO stability are proposed.