Effect of Thermal Fluctuations of Magnetization on Perpendicular Exchange Anisotropy in Mn-Ir / [Co / Pt]n Multilayers

Abstract

The dependence of perpendicular exchange anisotropy on the thickness of the ferromagnetic (FM) layer in Mn-Ir / [Co/Pt]n multilayers was investigated. The dependencies on temperature of saturation magnetization, Ms, in [Co / Pt]n multilayers having Co and Pt layers of various thicknesses were examined. The rate of decrease of Ms against temperature was large for thin-Co (< 1 nm) or thick-Pt layers (> 1 nm), which indicates that thermal fluctuations in magnetization were significant. The unidirectional anisotropy constant, JK, was reduced with the decreasing thickness of the interfacial Co layer in contact with the Mn-Ir layer. This suggested that perpendicular exchange bias was degraded by thermal fluctuations in FM magnetization during thermal annealing. The dependencies of JK on the thicknesses of the Pt layer and inner Co layer could be also described by the thermal fluctuations in the magnetization of the FM layer.