Incoherent magnetization reversal process in discontinuous Fe₅₀Co₅₀/Ag multilayer thin films

The possibility of incoherent magnetization reversal process in annealed Fe₅₀Co₅₀/Ag multilayer thin films has been studied. Small magnetoresistance was measured in as-deposited films; however, after annealing above 150°C, the highly mobile Ag atoms form bridges between the Ag layers, and the magnetoresistance increases. For example, after annealing at 225°C for 30 minutes, the TEM photographs show clearly the crosssection of a discontinuous multilayer structure, the coercivity is relatively small, and the magnetoresistance reaches its largest value. This is explained by the formation of elongated clusters of disk-like ferromagnetic FeCo particles, the exchange coupling between these particles is weak due to the presence of Ag layer between them. In this case, an incoherent magnetization reversal process is assumed to be dominant. For samples annealed above 250 °C, these disk-like ferromagnetic particles within a column grow larger due to diffusion. The exchange interaction increase due to the Ag atoms migrating to the bridges between the columns and decreasing the distance between disk-like ferromagnetic particles. The coercivity of the film then increases, and a coherent magnetization reversal process is assumed to become dominant.