Effects of Co layer thickness and annealing temperature on the magnetic properties of inverted [Pt/Co] multilayers

Abstract

The effects of Co layer thickness and annealing temperature on the perpendicular magnetic anisotropy (PMA) properties of inverted [Pt (0.2 nm)/Co (t(Co))](6) multilayers (where t(Co) indicates the thickness of the Co layer) have been investigated. The cross-sectional microstructure, as observed from the high-resolution transmission electron microscope images, shows a clear layered structure with atomically flat interfaces both in the as-deposited state as well as after annealing, indicating the interface effects for PMA. The effective PMA energy density (K-eff) increases significantly with an increase in t(Co) from 0.2 to 0.28 nm and then becomes almost saturated with further increases in t(Co), followed by a slight reduction at the highest Co thickness, t(Co) - 0.6 nm. In order to explain the t(Co) dependence on K-eff, the intrinsic PMA energy density (K-i) is calculated by additionally measuring a similar set of results for the saturation magnetization. The K-i value increases nearly linearly with the increase in t(Co) from 0.2 to 0.5 nm, followed by saturation at a higher t(Co) value of 0.6 nm. Owing to a close relationship between K-i and the quality of the interfaces, these results indicate a similar t(Co) dependence on the quality of the interfaces. This is further supported from the magnetic measurements of the samples annealed at the highest temperature of 500 degrees C, where a second phase is formed, which show a similar t(Co) dependence on the amount of the second phase. The K-i value is nearly independent of the annealing temperature at t(Co) <= 0.4 nm, above which a substantial reduction is observed, when the annealing temperature exceeds 500 degrees C. (c) 2013 AIP Publishing LLC.