The theory of ultrasoft magnetic films

We propose a theoretical interpretation of the unusual magnetic properties of ultrasoft magnetic films. Effective-medium theory is shown to reproduce remarkably well the dependence of the low-frequency susceptibility with magnetic field. In order to understand the dynamical susceptibility, one needs to generalize the usual Landau–Lifshitz equation and introduce an anisotropic dissipative term. The two relaxation coefficients α1,α2 are determined by a fit of the experimental data. α2 is found to be large, perhaps reflecting the strong inhomogeneity of the local anisotropy field.