Magnetoresonance Properties of Nanogranular Films Cofeb-Linbo

Using the method of ferromagnetic resonance (FMR) in a wide range of frequencies of 7 - 37 GHz and temperatures of 4.2 - 320 K, the features of the magnetic dynamics of metal-dielectric nanocomposite (CoFeB)x(LiNbO3)100-x films with different concentrations of the ferromagnetic (FM) phase x were studied in the vicinity of metal-insulator transition. At room temperature, the dependence of the position and shape of the resonance peak on the concentration of the FM phase x was studied. With a change in the content of the metallic FM phase and the transition of the metal-insulator boundary in the studied nanocomposite, a substantial modification of the FMR spectra occurs. In the dielectric phase, a wide asymmetric absorption line is observed, due to the spread of local anisotropy of weakly interacting granules. In this case, the surface anisotropy of the granules plays a significant role. In the metal phase, the strong interaction between the FM granules leads to the formation of a magnetically uniform film. Under these conditions, the width of the FMR line is described by a two-magnon scattering model. Possible reasons for the appearance of additional absorption peaks in normal geometry for samples with a high content of the FM phase are discussed. One of the probable reasons is the excitation of surface spin-wave resonance modes in such films, which may be due to the appearance of a significant exchange stiffness of the film material upon transition to the metal phase. Based on experimental data on the temperature dependences of the line width ∆H II и ∆H ⊥, estimates of the dependence of the values of local fluctuations of the perpendicular and parallel anisotropy fields on temperature, as well as the parameter of the two-magnon scattering Γ_TMS are obtained. It is shown that the main role in the broadening of the FMR line is played by inhomogeneities associated with the spread of local anisotropy axes in the film plane. This effect can be explained by the presence of perpendicular surface anisotropy of granules. In the low-temperature region, unusual features of the behavior of the width and shift of the FMR line, typical for the mechanism of slow relaxation on paramagnetic impurities, were discovered. The experimental dependences δH (T) and ΔH (T) are consistent with the theoretical curves obtained in the framework of the proposed approach.