Effect of Cr concentration gradient on the intergranular exchange in CoCr(Ta,Pt) thin films.

Intergranular exchange in CoCr-alloy polycrystalline thin films utilized for longitudinal recording media is analyzed in terms of details of their chemical composition. Two neighboring interacting grains are modeled by a linear "atomic" chain extending from the center of one grain to the center of another. The composition at each spin site determines the interspin exchange interaction. Thermal fluctuations are included via mean field theory and they yield spacial variations of the saturation magnetization and the crystal anisotropy that differ from the bulk properties. Equilibrium spin configurations for the linear chain are obtained for different Cr concentrations at the grain boundary and for different temperatures. Chromium segregation at the boundary is confirmed to be the mechanism for grain decoupling. An effective exchange parameter, assuming uniformly magnetized grains like those in large-scale micromagnetic simulations, is determined. This parameter decreases significantly with increasing temperature and increases slightly with relative anisotropy axis orientation. [ABSTRACT FROM AUTHOR]