Magnetization reversal and giant coercivity in Sm-Co/Cu-Ti particulate films

Highly coercive granular SmCo/CuTi films were produced by thermal processing of sputtered SmCo₅/(CuTi) multilayers and investigated experimentally and theoretically. Electron microscopy shows that the processed films consist of spherical grains that have diameters of 5-10 nm and are embedded in a matrix. Both the grains and the matrix phase exhibit the CaCu₅ structure, but the matrix is probably Cu-rich. The films have high coercivities of up to 50.4 kOe at 300 K. Analytical calculations and micromagnetic simulations yield a transition from a nucleation-type weak-interaction regime to a discrete-pinning-type strong-interaction regime. The transition occurs at packing fractions similar to those encountered in the investigated films and is accompanied by a coercivity maximum.