Brillouin light scattering observation of the transition from the superparamagnetic to the superferromagnetic state in nanogranular (SiO2)Co films

Abstract

Evolution of magnetic excitations from purely magnetostatic modes to dipole-exchange spin waves in the Damon–Eshbach geometry in nanocomposite (SiO2)100−xCox (50 at. %<x<80 at. %) films during a transition from superparamagnetic to superferromagnetic state has been studied by Brillouin light scattering. It has been shown that removal of the degeneracy of backward volume magnetostatic waves due to nonzero exchange constant manifests itself in more pronounced Stokes/anti-Stokes asymmetry. Accompanying static characterization by means of magnetic force microscopy imaging and grazing incidence small angle neutron scattering has demonstrated the presence of weak stripe domains in the superferromagnetic phase.