Coercivity enhancement of Co/Pt superlattices through underlayer microstructure modification

A major effort is directed toward increasing the coercivity of Co/Pt superlattice films for practical applications. We have used amorphous ITO as the underlayer and have studied the microstructure and magnetic properties of Co/Pt multilayer film by varying the deposition conditions of the underlayer. We have correlated observed microstructural features with coercivity and squareness behavior. A smooth underlayer deposited at low pressure results in high squareness but low coercivity, whereas a rough underlayer deposited at high pressure produces Co/Pt films with low squareness but high coercivity. We attribute the increase in coercivity to a decrease in Co/Pt columnar diameter and to enhanced domain wall pinning because of morphology-induced micro-structural defects such as irregular interfacial and columnar boundaries, and a decrease in columnar diameter. The concurrent reduction in squareness is attributed to a decrease in anisotropy because of degraded crystallinity and admixture of fcc(200) texture. Underlayer morphology can be easily controlled by sputtering pressure for the optimum combination of coercivity and squareness.