AC conductance of (Co0.45Fe0.45Zr0.10)X(Al2O3)1−X nanocomposites

Abstract

The influence of the composition on the AC carrier transport of the composite films containing ferromagnetic CoFeZr nanoparticles in amorphous aluminium oxide matrix has been investigated. The films 3–5 μm in thicknesses and with variable composition 30 at.% < X < 60 at.% were sputtered on a single substrate from the compound target in the chamber with argon–oxygen gas mixture. TEM and SEM measurements and Mossbauer spectroscopy data have shown that all the studied films of (Co0.45Fe0.45Zr0.10)X(Al2O3)1 − X with 30 at.% < X < 65 at.% have revealed the structure with crystalline granular metallic alloy (with particles of a few nanometers in size) and amorphous alumina. AC conductance measurements were performed over the frequency range 102–106 Hz at temperatures from 80 to 330 K. DC conductance measurements have been carried out for this temperature region also. The presence of two critical regions for the metallic fraction (X1 = 33–40% and X2 = 50–55%), where diagram “electric property–composition” exhibited pronounced peculiarities, has been confirmed. A qualitative structural model of nanocomposite was offered to explain this behavior. In accordance with the model, the first critical region at X1 is associated with a shift of percolation threshold due to the formation of oxide layer on metallic nanoparticles, owing to the presence of oxygen in gas ambient during the sputtering process. The second critical region of the composition at X2 is ascribed to the formation of percolation net of magnetic metallic nanoparticles in the dielectric amorphous alumina matrix.