Abstract
The structure evolution of granular (NiFeCo)xAg(1-x) (x = 9-41 at%) films was characterized by x-rayphotoelectron spectroscopy, Rutherford backscattering spectroscopy, x-raydiffraction, atomic force microscopy and magnetic force microscopy. Thegiant magnetoresistance of the films was measured as a function oftemperature between 20 and 300 K using a conventional four-point probe dctechnique in the presence of a magnetic field up to 7.6 kOe. Thetemperature dependence of magnetization and magnetic hysteresis loops forthe films were measured by a SQUID magnetometer. It was found that theoptimum concentration and annealing temperature for the maximum giantmagnetoresistance was associated with the crystalline structure and themagnetic domain structure of the film. A clear flat-top parabola and asignificant deviation from the quadratic law expected for equal-size,non-interacting superparamagnetic particles in the magnetoresistance(Δρ/ρ) against magnetization (M/Ms) curve were observed forthe 500 °C annealed (NiFeCo)20Ag80 sample in awide field region. The curves of Δρ/ρ against M/Ms werewell described by a function of the form c(M/Ms)10. This behaviourwas explained by combining the characteristics of the microstructure,magnetic domain structure and magnetic properties of the sample.
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