Magnetoresistance properties of ion beam synthesized granular magnetic thin films

This work reports the observation of novel magnetoresistance (MR) propertie s of three kinds of granular magnetic thin films formed by high-dose implan tation using a metal vapor vacuum are inn source. For granular CoAg films p repared by Co implantation into thermally evaporated Ag films, giant magnet oresistance effects were observed as expected. However. the MR results exhi bit 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 larg e positive MR effect (larger than 700% for one sample at 30 K) at low-tempe ratures 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 exhi bits positive MR values in the order of a few percent at temperatures highe r 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 backsc attering spectromotry (RBS) and other characterization techniques. (C) 2000 Elsevier Science B.V. All rights reserved.