Spin torque driven dynamics of a coupled two-layer structure: Interplay between conservative and dissipative coupling
Résumé
The general concepts of spin wave theory are adapted to the spin torque driven dynamics of a self-polarized
system based on two layers coupled via interlayer exchange (conservative coupling) and mutual spin torque
(dissipative coupling). An analytical description of the nonlinear dynamics is proposed and validated through
numerical simulations. In contrast to the single layer model, the phase equation of the coupled system has a
contribution coming from the dissipative part of the LLGS equation. It is shown that this is a major contribution to
the frequencymandatory to describe well the most basic features of the dynamics of this coupled system.Using the
proposed model a specific feature of coupled dynamics is addressed: the redshift to blueshift transition observed
in the frequency current dependence of this kind of exchange coupled systems upon increasing the applied field.
It is found that the blueshift regime can only occur in a region of field where the two linear eigenmodes contribute
equally to the steady state mode (i.e., high mode hybridization). Finally, a general perturbed Hamiltonian equation
for the coupled system is proposed.