Coupling of spin-transfer torque to microwave magnetic field: A micromagnetic modal analysis

Micromagnetic computational spectral mapping technique is applied to analyze the magnetic oscillation modes excited by either a microwave circularly polarized magnetic field or a spin polarized current flowing through Permalloy (Py) spin valves. A complete study has been carried out on multilayers Py(10 nm)/Cu(5 nm)/Py(2.5 nm) with rectangular cross section (60×20 nm2). The magnetic normal modes obtained agree with recent analytical spin wave models in patterned nanostructures. When both excitations, microwave field and spin polarized current, are applied at the same time a complex coupling process is observed. The detailed micromagnetic analysis of the coupling shows three different stages: (i) The initial stage in which the magnetic normal modes are dominant, (ii) an intermediate stage showing an incoherent behavior, and (iii) the final stage where a persistent domain wall oscillation is present. Micromagnetic spectral mapping technique is shown to be an adequate tool for describing the temporal evoluti...

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