Giant magnetoresistance in granular Ag–Co films irradiated by excimer laser

Abstract

A series of Ag 100− x Co x films ( x varying from 10 to 30 at.%) were codeposited by two electron beam sources in UHV system at the Si/SiO 2 substrate temperature ≤40°C. The Ag 75Co 25 films were thermally processed by rapid thermal annealing (RTA) at 500, 750 and 1000°C for 30 s and by excimer laser irradiation at the fluences F=0.1, 0.15 and 0.2 J cm −2 and number of pulses n varying from 1 to 100. The samples were analyzed by X-ray diffraction (XRD) and grazing incidence XRD (GIXRD). The electrical resistance R( H) was measured up to 50 kOe with magnetic field perpendicular or parallel to the film plane and with current in plane of the sample, mostly at 4.2 K and 300 K. With increasing Co content in the film, a different degree of fcc Ag and fcc Co separation in the as-deposited films was found, and for x→30%, small fcc Co peaks appeared. With RTA, a pronounced phase separation and increasing grain size with increasing annealing temperature was observed. On the contrary, after laser irradiation, more random and less equilibrium structures with smaller grain size and even negative temperature coefficient of the resistance developed. The giant magnetoresistance (GMR) of Ag 75Co 25 films is ≈74% at 4.2 K and 11.3% at 300 K in the as-deposited state. The GMR at 4.2 K can be increased by XeCl irradiation to 82% at the most severe irradiation conditions ( F=0.2 J cm −2, n=10) and to 13.2–13.5% at 300 K at the applied fluences. The increase of GMR is ascribed to the formation of more random structure with smaller grain size.