Microwave dynamics in point contact spin valve structures combining in-plane and out-of-plane magnetic layers with in-plane magnetic fields

Point contact spin transfer devices combining perpendicularly and in-plane magnetized layers are good candidates to fulfill the requirements of high power, low line-width and close to zero applied field operation [1][2]. We present experimental results on spin transfer torque oscillators combining an extended out-of-plane (CoFe/Pd) magnetized layer and a lithographically patterned in-plane (CoFe) magnetized layer.
High frequency magnetization dynamics as a function of current in such devices are explored for in-plane applied magnetic field. In general, the recorded oscillation frequency is lower than that which would be expected for dynamics associated with a single layer in the device (calculated for the given Ha and Ms of each layer). The individual dynamics of each layer are calculated, individually, from numerical integration of the LLG equation taking into account the Slonczewski spin transfer torque including the spin transfer asymmetry characterized by λ [3]. Microwave oscillations are observed at zero applied magnetic field. However, due to canting of the perpendicular layer in the in-plane applied magnetic field, the current dependent frequency of the system changes slope when the relative magnetization orientations are changed from perpendicular to parallel.
A.M.D. and C.F. acknowledge financial support from the Swiss National Foundation Ambizione grant (PZ00P2_131808).
[1] Houssameddine, D. et al., Nature Mat. 6, 447 (2007).
[2] Rippard, W.H., et al., Phys. Rev. B. 81, 014426 (2010).
[3] Slonczewski, J.C., J. Magn. Magn. Mater. 247, 324 (2002).