MICROSTRUCTURE OF CO-AL-O GRANULAR THIN-FILMS

We have investigated the microstructures of Co-Al-O granular thin film s, which were prepared by the sputter-deposition technique with variou s oxygen partial pressures. The constituent phases, grain sizes of gra nular particles, and width of insulating channels have been evaluated quantitatively. The specimen with the optimum giant magnetoresistance (GMR) is composed of nanoscale Co particles, and these are completely isolated by amorphous aluminum oxide channels. The GMR behavior observ ed in the Co-Al-O films has a close correlation with the width of the insulating channel and the grain size of the magnetic particles, which is consistent with the spin-dependent tunneling conduction mechanism of GMR. (C) 1997 American Institute of Physics.