Magneto-transport properties of insoluble Ag-Co films with thin Co concentrations

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The aim of this research project is to understand the mechanism of magneto transport in insoluble AgCo granular thin folms. Thin folms of AgCo granular alloys with Co concentration between 10 and 0.6 at% were made with a conventional ultra high vacuum deposition technique. From the measurement of magnetization, samples before thermal annealing show superparamagnetism with blocking temperature below 20 K.The mean diameter deduced from a Langevin function fitting indicates the presence of clusters including Co atoms between 30 and 200, which depend on the concentration of Co and history of thermal annealing. The magneto-resistance of these materials does not saturate under an applied field of 55kOe and the ratio is several % at room temperatures and 20 % at low temperatures. The MR ratio increases with the increase of particle size while the resistance change has an opposite tendency against the particle sizes. Considering with the change in resistance of Ag matrix, it coincides qualitatively with the magneto-resistance change predicted by Asano et al. However, the ratio experimentally obtained has larger values of those theoretically predicted.Thermo-Electric Power (TEP) measurements of low Co concentration AgCo granular films show a steep increase of absolute value at low temperature and the change is getting gradual at higher temperatures while the samples after thermal annealing have almost linear temperature dependence. The linear depemdence originates form the scattering with the bulk like Co particles in Ag. The temperature dependence of TEP of 0.6% thin films is satisfactory explained by the superposition of Kondo effect, matrix contribution and bulk like Co particles.