On the susceptibility of ‘‘ultrasoft’’ magnetic films (abstract)

It has been shown1 that after suitable annealing, some amorphous films, e.g., Co61B39 exhibited ‘‘ultrasoft’’ properties: a very small value of the anisotropy field, and a highly damped dynamical susceptibility. We interpret the experimental susceptibility in the framework of the effective medium theory in two dimensions, which predicts that the transverse susceptibility goes from √μ in the disordered case, to μ in the completely magnetized case, where μ=M/(Ha+H). To interpret the dynamical susceptibility, we generalize the LL equation, and find a large damping parameter α. In both cases the agreement with experimental data is excellent. It is conjectured that such a value of α might be due to strong fluctuations of the local anisotropy.