|
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 degree(s)C for 30 s and by XeCl excimer laser irradiation at the fluences F equals 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 fcc Ag phase dominates. With RTA a pronounced fcc Ag and fcc Co phase separation and increasing grain size with increasing annealing temperature occur. On the contrary, after laser irradiation more random and less equilibrium structures with smaller grain size developed. This conclusion was confirmed by TEM and ED. The giant magnetoresistance (GMR) of Ag75Co25 films is equals 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 equals 0.2 Jcm-2, n equals 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 Rm obeys the power law Rm approximately -Tn with n equals 1.67. This dependence is ascribed to the electron-magnon interaction.
|
