The improvement of the giant magnetoresistance in granular Ag-Co films by excimer laser processing

Ag75Co25 films were codeposited by two electron beam sources in UHV system on the Si/SiO2 substrate. The films were thermally processed by rapid thermal annealing (RTA) at 500, 750 and 1000 degrees C for 30 s and by XeCl excimer laser irradiation at the fluences F=0.1, 0.15 and 0.2 Jcm(-2) and number of pulses n varying from 1 to 100. The samples were analyzed by X-ray diffraction (XRD), grazing incidence XRD, transmission electron microscopy (TEM) and selected area electron diffraction (ED). The electrical resistance R(H,T) was measured up to 50 kOe with magnetic field perpendicular or parallel to the film plane and with current in plane of the sample, from 4.2 K to 300 K. Angular dependence of R(H) was measured as well. The performance of films under laser irradiation was approximated by computer simulations of simplified structures. In the XRD spectra of as-deposited films well developed fee Ag phase dominates. With RTA a pronounced fee Ag and fee Co phase separation and increasing gain size with increasing annealing temperature occur. On the contrary, after laser irradiation more random and less equilibrium structures with smaller gain size developed. This conclusion was confirmed by TEM and ED. The giant magnetoresistance (GMR) of Ag75CO25 films is approximate to 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 laser irradiation to 82% at the most severe irradiation conditions (F=0.2 Jcm(-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 a more random structure with smaller grain size. The temperature dependence of magnetic contribution responsible for GMR R-m obeys the power law R(m)similar to-T-n with n=1.67. This dependence is ascribed to the electron-magnon interaction.