Magnetization and magnetoresistance in granular AgCo films

A series of 150 nm thick Ag100-xCox films (x varying from 12 at.% to 46 at.%) were grown by e-beam coevaporation in an UHV system at substrate temperatures, T-s, between 30 degrees C and 200 degrees C, followed by a heat treatment, For the analysis of the magnetic properties of the Co precipitates we fit our m(B) measurements with a log-normal distribution of radii using the Langevin function to obtain mean radii of the superparamagnetic particles. By annealing it is possible to optimize the giant magnetoresistance Delta rho/rho of samples grown at room temperature, whereas no heat treatment seems to be necessary for samples evaporated at elevated temperatures. These magnetic film properties are compared with the corresponding Co particle sizes and size distributions. The film structure and morphology was determined ex situ by X-ray diffraction. Our results of the magnetic film properties an consistent with the observed changes in microstructure and Co particle growth.