Tunneling magnetoresistance and electron spin resonance study on Co-Al-O granular films

In this work, a series of Co-Al-O granular films were prepared using an Ar-O-2, reactive rf sputtering system. The optimal magnetoresistance (MR) ratio of 5.1% at room temperature was found in Co44Al23O33 sample. After annealing at 300degreesC, MR ratio can be raised to 6.1%. We also measured the spectra of electron spin resonance for this series of samples and found an interesting correlation between the magnitude of MR ratio and the width of absorption field (DeltaH). Our results show that the maximum tunneling magnetoresistance occurs when DeltaH is the largest, indicating the important role of magnetic microstructure in the mechanism of granular tunneling. (C) 2002 Elsevier Science B.V. All rights reserved.