Spin transfer oscillators with different geometries

For applications one requires high power, narrow line-width oscillators which can operate ideally at zero field. Spin transfer torque can induce precession in GMR and TMR spin valves.
There are recent demonstrations of out of plane precession in both in-plane and perpendicular magnetic free layers. Here, we calculate the outputs by solving the LLGS equations for these two geometries. We find that the system with perpendicular free layer is advantageous for two reasons: a further reference layer is not required as the polarising layer itself acts as a reference layer for the GMR effect; precession is independent of the initial magnetisation state, that is various magnetisation directions can be excited into precession at specific fields and currents.