High-frequency spin-dependent tunnelling in magnetic nanocomposites: Magnetorefractive effect and magnetoimpedance

Since the dielectric permittivity is linear with frequency-dependent conductivity, high-frequency properties for any kind of magnetic materials with the high magnetoresistance depend on magnetization. It manifests as magnetorefractive effect (MRE) in the infrared region of spectrum and as magnetoimpedance (MI) in the frequency range between radio and microwaves. The main mechanism of both MRE and MI in nanocomposites with tunnel-type magnetoresistance is high-frequency spin-dependent tunnelling. We report on recent results of theoretical and experimental investigations of MRE and MI in nanocomposites Co51.5Al19.5O29, Co50.2Ti9.1O40.7, Co52.3Si12.2O35.5 and (Co0,4Fe0,6)48(MgF)52. Most of the obtained experimental data for MRE and MI are consistent with the theory based on considering the tunnel junction between adjacent granules in percolation cluster as a capacitor.