SYNTHESIS AND MAGNETIC-PROPERTIES OF NI-AL2O3 THIN-FILMS

Ni-Al2O3 nanocomposite thin films have been produced on sapphire, sili con, and silica substrates by a combination of sol-gel processing and partial reduction reactions. Transmission electron microscopy shows Ni particles, similar to 20 nm in diameter, embedded in slightly larger diameter alumina grains. X-ray diffraction lattice parameter measureme nts suggest that the Ni is in a state of nonhydrostatic strain; Magnet o-optical Kerr effect measurements indicate that the Ni particles in t he films on the silicon and silica substrates support perpendicular ma gnetization. The saturation Kerr rotation increases linearly with film thickness to values above pure Ni and independent of reflectivity, in dicating that the material is behaving as a Faraday rotator. The enhan ced magnetic properties of the composite films are related to the nonh ydrostatic strain developed in the Ni particles during fabrication. It is argued that the strains originate from the coefficient of thermal expansion mismatch between the film and substrate, and likely the volu me shrinkage associated with the reduction reaction. (C) 1997 American Institute of Physics.