Brillouin light scattering intensities for a thin film exchange coupled to a bulk magnetic substrate

Abstract

Brillouin light scattering intensities vs. frequency shift have been calculated for a complex structure consisting of a bulk magnetic substrate, a nonmagnetic spacer layer, a thin magnetic film a few monolayers thick, and a thin nonmagnetic overlayer. The calculations have been carried our for the back-scattering configuration with an applied magnetic field in the plane of the specimen using a modification of the formalism described by Camley and Mills. The thin film magnetization has been assumed to be coupled to the bulk surface magnetization by an exchange energy of the form Ex = − J1cosθ + J2cos2θ erg/cm2, where θ is the angle between the directions of the thin film magnetization and the bulk surface magnetization. The theory gives a good account of the field-dependent frequency shifts measured using Fe(0 0 1) whisker/Cr(0 0 1)/Fe(0 0 1)/Au(0 0 1) structures. Such experiments can be used to obtain values for the coupling parameters, J1 and J2, without having to use micromagnetic calculations to interpret the applied field dependence of the thin film and bulk magnetization orientations. The theory can also be used to obtain the total coupling strength. JEX = J1 - 2J2, even when this coupling strength is positive, corresponding to ferromagnetic coupling, provided that JEX is not too strong (∼ 1 erg/cm2 or less for the whisker/Fe system).