Growth, structural, and magnetic properties of high coercivity Co/Pt multilayers

Abstract

Electron beam evaporated Co/Pt multilayers {[Co(tConm)/Pt(1 nm)]10, 0.2<tCo<2 nm} with perpendicular magnetic anisotropy and room temperature coercivities Hc = 2- 15 kOe are studied as a function of growth temperature TG. Hysteresis loops and magnetic force microscopy (MFM) indicate changes in the magnetization reversal mechanism along with a sharp increase in coercivity for TG≳230-250°C. Films grown at TG<230°C (TCo = 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 Hn~Hc. Films grown at TG>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. © 2001 American Institute of Physics.