Magneto-transport properties in perpendicularly magnetized magnetic tunnel junctions using an Mg40Fe10O50 tunnel barrier

We develop perpendicularly magnetized magnetic tunnel junctions (MTJs) consisting of a CoFeB/Mg40Fe10O50 (MgFeO)/CoFeB multilayer. The use of MgFeO yields a substantial improvement in the flatness of the MTJ film stack compared with conventional MTJ films using MgO as a tunnel barrier layer, and a 1.7 times enhancement in the perpendicular magnetic anisotropy energy is obtained for the ultrathin CoFeB layer deposited on the MgFeO layer. Nanostructural analysis combined with elemental distribution mapping reveals the formation of highly (001)-oriented MgFeO in the as-deposited MTJ film, and the crystalline MgFeO layer effectively inhibits diffusion of B atoms from the CoFeB layers through the tunnel barrier layer during the post-annealing process. Accordingly, the MgFeO-MTJ exhibits exceptional stability against high temperature annealing, and a large tunnel magnetoresistance ratio of 235% is demonstrated in MTJ nanopillar devices after annealing at 400 °C. Ferromagnetic resonance measurements also reveal a reduced magnetic damping in the MgFeO-MTJs owing to the improved uniformity in the CoFeB layer. The present experimental results will facilitate the development of magnetoresistive memory devices with increasing memory density and higher energy efficiencies.