Effective Damping Contribution From Micromagnetic Modeling in a Spin-Transfer-Driven Ferromagnetic Resonance

Spin-transfer-driven ferromagnetic resonance is theoretically analyzed in a Py/Cu/Py spin valve with elliptical cross-sectional area (90 nm times 30 nm) by means of macrospin and micromagnetic simulations. An additional damping contribution to the Gilbert parameter is obtained when the spatial dependence of the magnetization is taken into account. These results are used to quantitatively explain the large value of the damping parameter found in the experiments by Sankey et al. [Phys. Rev. Lett. 96, 227601 (2006)]. The dependence of this additional damping on the dc bias is also studied, and the strength of the nonuniformities is quantified by means of a phenomenological expression.