Growth, Structural, and Magnetic Properties of High Coercivity Co/Pt Multilayers

Electron beam evaporated Co/Pt multilayers {[Co(t Co nm)/Pt(1 nm)]10, 0.2 < t Co < 2 nm} with perpendicular magnetic anisotropy and room temperature coercivities H c = 2–15 kOe are studied as a function of growth temperature T G. Hysteresis loops and magnetic force microscopy (MFM) indicate changes in the magnetization reversal mechanism along with a sharp increase in coercivity for T G ≥ 230–250°C. Films grown at T G < 230°C (t Co = 0.2–0.4 nm) show micrometer size magnetic domains and rectangular hysteresis indicating magnetization reversal dominated by rapid domain wall motion following nucleation at H n~H c. Films grown at T G > 250°C show fine-grained MFM features on the sub-100 nm length scale indicating reversal dominated by localized switching of small clusters. High-resolution cross-sectional transmission electron microscopy (TEM) with elemental analysis shows columnar grains extending throughout the multilayer stack. Co depletion and structural defects at the grain boundaries provide a mechanism for exchange decoupling of adjacent grains, which may result in the high coercivities observed.