Magnetoresistance properties of ion beam synthesized granular magnetic thin films

Abstract

This work reports the observation of novel magnetoresistance (MR) properties of three kinds of granular magnetic thin films formed by high-dose implantation using a metal vapor vacuum arc ion source. For granular CoAg films prepared by Co implantation into thermally evaporated Ag films, giant magnetoresistance effects were observed as expected. However, the MR results exhibit an anomalous temperature variation of the coercive field which shows a maximum at around 240 K and decreases with decreasing temperature from 240 to 20 K. For granular thin layers formed by Fe implantation into Si, a large positive MR effect (larger than 700% for one sample at 30 K) at low-temperatures was observed. For thin layers formed by Ti implantation into Si at appropriate implant conditions, an even more unexpected positive MR effect was observed. The MR effect virtually vanishes at low-temperatures but exhibits positive MR values in the order of a few percent at temperatures higher than about 240 K. The magnetic field dependence and temperature variation of these MR properties, and their relation with the processing conditions were studied and discussed in conjunction with results of Rutherford backscattering spectrometry (RBS) and other characterization techniques.