Evaluation of higher order magnetic anisotropy in a perpendicularly magnetized epitaxial ultrathin Fe layer modified by applied voltage

摘要

Recently, voltage-controlled magnetic anisotropy (VCMA) effect at an interface between a ferromagnetic metal layer and a dielectric layer attracts much attention as the key technology for voltage-torque magnetic random access memory (MRAM). For the stable operation, VCMA coefficient ξ is important factor and required to be 600-1500 fJ/Vm.) However, demonstrated ξ value (≤290 fJ/Vm) in magnetic tunnel junctions (MTJs) is much lower than the required value and its improvement is the current main issue. To make a strategy to improve ξ value, we need more systematic studies focusing on the relationship between magnetic anisotropy and VCMA effect which give clues to clarify the mechanism of VCMA effect. In this study, we investigated the thickness and applied voltage dependences of first and second order magnetic anisotropy, K1 and K2 respectively, in an ultrathin Fe film.