Effect of annealing on the giant magnetoresistance and magnetic properties of pulse-electroplated Co-Cu granular alloy films

摘要

Granular alloy films Co_xCu_(1-x) (0.17≦x≦0.66) were prepared by pulse plating. Although a second phase,probably hexagonal close-packed phase, was present in the X-raydiffraction pattern for all samples examined, the matrices showedthe face-centered cubic lattice parameter decreasing almost linearlywith increasing x. The magnetoresistance (MR) of films was foundto be larger after annealing at an appropriate temperature between400 deg C and 600 deg C. A maximum value of the MR ratio ofabout 4.2 percent was observed at the composition around x=0.2.the remanence ratio was found to be 0.4-0.6 for all films measured,indicating the presence of ferromagnetically interacting particleseven in the as-deposited condition and to depend little on thecomposition. The average size of magnetic particle D for x=0.31estimated using M(H) data at room temperature was found to beabout 9.7 nm before annealing and 12 nm after annealing at 450deg C. The large magnetic particle size in the as-deposited stateseems to be the main cause of the small MR value.