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)greater than or similar to 230-250 degreesC. Films grown at T-G < 230 degreesC (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 similar to H-c. Films grown at T-G > 250 degreesC 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. (C) 2001 American Institute of Physics.