Ion-beam modification of Co/Ag multilayers I: Structural evolution and magnetic response

We describe the effects of 1 MeV Si+ ion-beam irradiation on a sputtered Co /Ag multilayer with layer thicknesses of 5 A for Co and 25 A for Ag, thickn esses for which the magnetoresistance is maximum in the as-deposited sample . X-ray diffraction, magnetization, and magnetoresistance measurements all point to the conclusion that the Co is initially dispersed through the Ag a nd segregates completely upon ion-beam bombardment. Throughout the process both Ag and Co grains maintain a high degree of texture, essentially face c entered cubic (111). The magnetization behavior evolves from superparamagne tic to mixed superparamagnetic-ferromagnetic with ion dose whereas the room -temperature magnetoresistance decreases from 12% to 1.5% upon irradiation up to 5x10(16) Si+/cm(2). Simple models taking into account the size distri bution of the Co particles have been used to analyze these phenomena in ord er to quantify the particle size distribution. (C) 2000 American Institute of Physics. [S0021-8979(00)09512-8].