Computational study of microwave oscillations in nonstandard spin valves in the diffusive transport limit

Authors:

• E. Jaromirska,
• Pavel Balaz,
• L. López Díaz,
• Józef Barnaś

Abstract

An anomalous (inverse) 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. 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 Co(8 nm)/Cu(10 nm)/Py(8 nm) nanopillar, considering geometry with extended and etched Co layer. In both cases we specify conditions for the out-of-plane 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. © 2010 The American Physical Society.