Structural and magnetic properties of iron oxides in co-sputtered granular thin films

Granular Fe-V2O5 thin films with different iron concentrations prepared by means of radiofrequency magnetron co-sputtering technique were investigated by means of X-ray; diffraction, Transmission Electron microscopy and Fe-57 Mossbauer spectrometry as a function of iron concentration. A common experimental feature reveals that a percolation-like threshold occurs at around 23-25% atomic Fe. Below such a critical value, the co-sputtering process favours the presence of ultrafine amorphous oxide grains with sizes lower than 10 nm embedded in a vanadium oxide matrix. Above, one clearly observes the presence of fine grains (sizes comprised between 10-100 nm) composed of either hematite or maghemite phases dispersed in the same matrix, the set displaying a magnetic order at room temperature.