High field magnetoresistance in Co–Al–O nanogranular films

We have studied magnetic and electrical transport properties of Co–Al–O nanogranular films. The films prepared by laser ablation consist of Co particles embedded in an insulating Al2O3 matrix. Different current–voltage characteristics are observed depending on Co concentration in the films. Tunneling magnetoresistance (TMR) shows an anomalous behavior in high magnetic fields at low temperatures. The presence of magnetic atoms dispersed in the insulator is a possible explanation of the observed anomaly of the TMR.