Micromagnetic Modeling of Non-Linear Spin Dynamics in Confined Geometries
V. Novosad, S.-T. Chui, F.Y. Fradin, M. Grimsditch, S.D. Bader
Argonne National Laboratory, US
Keywords: micromagnetic modeling, non-linear spin dynamics, spin wave hybridization, microwave-assisted magnetization reversal
Abstract:We have recently reported spin wave properties of 0.5 x1 nm x 20nm Fe20Ni80 ferromagnetic particles subjected to an external rf field using microwave-assisted BLS . We discovered appearance of sub-structure in the Ferromagnetic Resonance (FMR) in the nonlinear regime, in addition to an expected frequency decrease and line broadening. Here, we will describe the details of micromagnetic modeling to explain observed phenomenon. The modeling results reproduce the main findings of the experiment. We speculate that the complexity of the spectra at the higher rf power is due to hybridization of the FMR mode to other magnetostatically dominated modes characteristic of confined nanomagnets. Spin distributions calculated below the FMR, at its peak, and above the peak favor this idea. The uniform rf fields should couple strongly only to excitations with a significant q=0 Fourier component. Because of nonuniform shape of the nanomagnets, spin wave states of different q’s appears to be are coupled and more than one excitation can exhibit a significant q=0 response. This could be of interest to control the magnetization reversal mechanism in submicron-size Magnetic Random Access Memory devices via excitation of particular spin wave modes.  M. Grimsditch, et al., PRL 96, 047401 (2006).