Faraday rotation of surface-oxidized metal fine particles clustered in dielectric matrix (abstract)

Abstract

Off diagonal terms (which give magneto-optical effects) of ‘‘effective dielectric tensor’’ of composite material with magnetic fine particles dispersed in a dielectric matrix have been derived by the authors.1 In this study, we extended the effective tensor to the composite in which surface-oxidized metal ferromagnetic fine particles are clustered in the matrix. We proposed ‘‘magnetic cluster model’’ as follows. The surface-oxidized metal particles of size d, which is much smaller than light wavelength λ (d≪λ), aggregate in the matrix to form the magnetic clusters of average size D which is much larger than the wavelength (D≫λ). The composite as a whole contains the magnetic clusters at a volume fraction of F(0<F<1). In the cluster the surface-oxidized metal particles are dispersed at an average volume fraction of f(0<f<1). The surface-oxidized metal particles contain metal at an average volume fraction of g(0<g<1). Since d≪λ, we can apply to the magnetic fine particle the effective dielectric tensor, in terms of which we can calculate the effective dielectric tensor of the magnetic cluster. On the contrary, we cannot apply the effective tensor to the composite as a whole, because D≫λ. However, Faraday rotation of the composite is given by F times the Faraday rotation of the magnetic clusters which is expressed in terms of the effective dielectric tensor of the cluster. Faraday rotation spectrum was measured at λ=0.5–0.8 μm for a composite film (0.25 μm in thickness) in which Ni fine particles (∼20 μm in size) were dispersed in PVC (polyvinyl chloride) matrix by spin coating. The result was successfully interpreted by our magnetic cluster model assuming parameters F=0.15, f=0.78, g=0.9, which conforms to our experimental conditions.