Structure evolution, magnetic properties and giant magnetoresistance of granular NiFeCo-Ag films

The structure evolution of granular (NiFeCo)(x)Ag(1-x) (x = 9-41 at %) films was characterized by x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, x-ray diffraction. atomic force microscopy and magnetic force microscopy. The giant magnetoresistance of the films was measured as a function of temperature between 20 and 300 K using a conventional four-point probe de technique in the presence of a magnetic field up to 7.6 kOe. The temperature dependence of magnetization and magnetic hysteresis loops for the films were measured by a SQUID magnetometer. It was found that the optimum concentration and annealing temperature for the maximum giant magnetoresistance was associated with the crystalline structure and the magnetic domain structure of the him. A clear Bat-top parabola and a significant deviation From the quadratic law expected for equal-size, non-interacting superparamagnetic particles in the magnetoresistance (Delta rho/rho) against magnetization (M/M-s) curve were observed for the 500 degrees C annealed (NiFeCo)(20)Ag-80 sample in a wide field region. The curves of Delta rho/rho against M/M-s were well described by a function of the form c(M/M-s)(10). This behaviour was explained by combining the characteristics of the microstructure, magnetic domain structure and magnetic properties of the sample.