  Spin-transfer torque and current induced spin dynamics in spin-valve
nanopillars with the free magnetic layer located between two magnetic films of
fixed magnetic moments is considered theoretically. The spin-transfer torque in
the limit of diffusive spin transport is calculated as a function of magnetic
configuration. It is shown that non-collinear magnetic configuration of the
outermost magnetic layers has a strong influence on the spin torque and spin
dynamics of the central free layer. Employing macrospin simulations we make
some predictions on the free layer spin dynamics in spin valves composed of
various magnetic layers. We also present a formula for critical current in
non-collinear magnetic configurations, which shows that the magnitude of
critical current can be several times smaller than that in typical single spin
valves.
