Nanogranular Co-Al-O films prepared by laser ablation

Nanogranular Co-Al-O films were prepared by pulsed laser deposition from Co-x(Al2O3)(1-x) targets. Three targets, with different Co volume fractions, were used in order to study the influence of the film composition on magnetic and transport properties. The samples deposited on room temperature substrates exhibit a granular structure consisting of Co grains with the size of few nm embedded in an insulating Al2O3 matrix. The magnetic properties show a gradual transition from a low temperature blocked regime to a high temperature superparamagnetic state. It is confirmed by the disappearance of magnetic hysteresis at high temperatures and the temperature dependence of magnetization. Magnetoresistance (MR) higher then 9% at 20 K can be found in Co26Al23O51 film. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.