Magnetic clusters, intergranular exchange interaction and their microstructural basis in thin film longitudinal media

We have experimental examined the micromagnetic structure in CoCrTa/Cr films deposited onto NiP/Al substrates at 25, 100, 150 200 and 250/spl deg/C. We prepared all the films in an ac-erased magnetic state. The Lorentz transmission electron microscopy images demonstrate a monotonic decrease of magnetic cluster size with increase of deposition temperature and the magnetic force microscopy results show a decrease of image contrast. This indicates a decrease of intergranular exchange coupling with increase of deposition temperature. Nanoprobe energy dispersive spectroscopy (EDS) reveals an increase of Cr segregation at CoCrTa grain boundaries with increase of deposition temperature. The correlation of micromagnetic and microcompositional observation supports that Cr segregation at grain boundaries is responsible for decoupling CoCrTa grains. Our nanoprobe EDS results also indicate that the Cr diffuses to the grain boundaries from the diffusion process involving the Cr underlayer.