  An anomalous (inverse) spin accumulation in the nonmagnetic spacer may build
up when the spin valve consists of magnetic films having different spin
symmetries. This leads to wavy-like 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 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 neglecting thermal fluctuations. We prove the assumption of wavy-like
torque angular dependence to be fully consistent with experimental
observations. We also show that some features reported experimentally, like
nonlinear slope of frequency vs. current behavior, are beyond the applicability
range of macrospin approximation and can be explained only by means of full
micromagnetic analysis.
