A new technique for ferromagnetic resonance calculations

A new approach for calculating high-frequency response spectra of ferromagnetic materials exhibiting inhomogenous configurations is presented here. Our software (GL_FFT copyright CNRS, Lab. Louis Néel, Grenoble) is based on the direct numerical integration of the Landau–Lifschift–Gilbert equation (noted LLG hereafter) using a finite difference method coupled with FFT techniques for the calculation of demagnetizing fields. Our technique is well adapted to simulate the magnetization dynamics and the relaxation processes in thin magnetic films. The dynamic Polder tensor P(ω) is deduced from the time–frequency transformation of the response δm(t) of the space average magnetization due to a weak uniform magnetic excitation δh(t). The whole spectrum is obtained from only one relaxation process, by using a step function for the excitation. Our technique is compared to the so-called dynamic matrix technique obtained by linearizing the LLG equation. Its application to epitaxial FePd thin films with perpendicular anisotropy is finally presented.