Dynamic magnetic permeability of the heterogeneous nanosystems based on (Co 41 Fe 39 B 20 ) x (SiO 2 ) 100 – x composites

Thin films of (Co41Fe39B20) x (SiO2)100 – x nanocomposites and hybrid nanocomposite–semiconductor [(Co41Fe39B20) x (SiO2)100 – x /C]50 multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co41Fe39B2O nanogranules in an SiO2 matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x per, where x per is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.