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An anomalous ͑inverse͒ spin accumulation in the nonmagnetic spacer may build up when the spin valve consists of magnetic films having different spin asymmetries and spin-diffusion lengths ͓J. Barnaś, A. Fert, M. Gmitra, I. Weymann, and V. K. Dugaev, Phys. Rev. B 72, 024426 ͑2005͔͒. This leads to wavylike dependence of spin-transfer torque on the angle between magnetizations, as predicted by spin-dependent diffusive transport model, and also confirmed experimentally. Making use of these predictions, we have numerically studied the magnetization dynamics in the presence of such a wavy torque in Co͑8 nm͒/Cu͑10 nm͒/Py͑8 nm͒ nanopillar, considering geometry with extended and etched Co layer. In both cases we specify conditions for the out-ofplane precession to appear in absence of external magnetic field and thermal fluctuations. We prove the assumption of wavylike torque angular dependence to be fully consistent with experimental observations. We also show that some features reported experimentally, such as nonlinear slope of frequency vs current, are beyond the applicability range of the macrospin approximation and can be explained only by full micromagnetic analysis.

Current-induced spin-transfer torque in spin valve structures with magnetic layers made of different materials can exhibit a nonstandard, i.e., wavy like, angular variation. Following the diffusive spin transport model, the wavy torque was theoretically found in the Co(8nm)∕Cu(10nm)∕Py(8nm) spin valve, and later was also experimentally confirmed. However, the single domain (macrospin) approximation fails to describe some features of magnetic dynamics observed in experiments, especially the frequency agility with current and its slope for the out-of-plane precessions. Therefore, we have revisited the abovementioned pillar structure and analyzed the conditions for the appearance of the out-of-plane oscillations. In particular, we have studied the possibility of triggering these modes by means of a moderate external magnetic field. We have identified modes supported within the macrospin model and verified the results by full micromagnetic simulations, revealing numerous qualitative discrepancies. For instance, the out-of-plane oscillations have been found in the macrospin model, whereas no such precessions have been observed in micromagnetic simulations even with an external magnetic field.

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