Mechanisms of FMR line broadening in CoFeB-LiNbO3 granular films in the vicinity of metal-insulator transition

Abstract

Metal-insulator (CoFeB) x (LiNbO 3 ) 100−x nanocomposite films with different content of the ferromagnetic (FM) phase x are investigated by ferromagnetic resonance (FMR) technique. A strong change of the FMR line shape is observed in the vicinity of metal-insulator transition (MIT) of the film, where the hopping-type conductivity σ modifies to the regime of a strong intergranular tunnelling, characterized by a logarithmic dependence σ(T ) at high temperatures. It is shown that below MIT, the FMR linewidth is mainly determined by the inhomogeneous distribution of the local anisotropy axes in the film plane. Above MIT, the contribution of this inhomogeneity to the line broadening decreases. At the same time, two-magnon magnetic relaxation processes begin to play a significant role in the formation of the linewidth. The observed behaviour indicates the critical role of interparticle exchange in the tunnelling regime above MIT of the nanocomposite.

Magnetic Anisotropy of Needlelike Single-Crystal MnSb Inclusions in an InSb Matrix

“…According to scanning electron microscopy (SEM) data, the average distance D between needles is ~25 μm and their diameter is d ~ 5 μm. The contribution from the dipoledipole interaction to the effective MA field is determined by factor (d/D) 2 and can be estimated using the formula 4πM S (d/D) 2 [17,18]. Its value is ~375 Oe, which makes up ~2% of the experimental value of 15 kOe.…”