Impedance and magnetization of CoFeZr nanoclusters embedded into alumina matrix

Influence of metal-to-dielectric ratio in (CoFeZr)x(Al2O3)100-x composites and influence of gas ambient in sputtering chamber on the impedance and magnetization of the films containing soft ferromagnetic Co0.45Fe0.45Zr0.10 nanoclusters in amorphous alumina matrix have been investigated. The films of 3-5 μm in thicknesses and with variable composition of 30 at.% < x < 60 at.% were sputtered on a single substrate from the compound target in the chamber containing argon or argon-oxygen gas mixture. The threshold character of impedance and magnetization behavior for the studied films was found to be in agreement with the earlier results obtained from dc carrier transport, magnetotransport and Mössbauer measurements. The change of electronic transport mechanisms from hopping (exponential) to metallic (power-like) behavior and the change of magnetic state from superparamagnetic to ferromagnetic beyond the percolation threshold concentration of xc ∼ 45-47 at.% for the films deposited in pure argon atmosphere were observed. The films sputtered in argon-oxygen gas mixture revealed that their conservation of hopping mechanism of ac electronic transport and superparamagnetic or non-magnetic state was due to the formation of semiconducting FeCo-based oxide shells separating metallic nanoclusters even beyond the percolation threshold of xc ∼ 55 at.%.