Perpendicular magnetic anisotropy in ultra-thin Cu2Sb-type (Mn-Cr)AlGe films fabricated onto thermally oxidized silicon substrates

Perpendicularly magnetized films exhibiting small saturation magnetizations ( M s) are essential for spin-transfer-torque magnetoresistive random access memories (MRAMs). In this study, the intermetallic compound (Mn-Cr)AlGe with a Cu2Sb crystal structure was investigated as a material exhibiting low M s ( similar to 300 kA/m) and high-perpendicular magnetic anisotropy energy ( K u). The layer thickness dependence of K u and effects of Mg-insertion layers at the top and bottom (Mn-Cr)AlGe|MgO interfaces were studied for film samples fabricated onto thermally oxidized silicon substrates to realize high K u values in the thickness range of a few nanometers. The values of K u were approximately 7 x 10 5 and 2 x 10 5J/m(3) at room temperature for 5 and 3nm-thick (Mn-Cr)AlGe films, respectively, with an optimum annealing temperature of 400 degrees C and Mg-insertion thicknesses of 1.4 and 3.0nm for the top and bottom interfaces, respectively. The Mg insertions were relatively thick compared with results of similar studies of the insertion effect on magnetic tunnel junctions. Cross-sectional transmission electron microscope images revealed that the Mg-insertion layers acted as barriers to the interdiffusion of Al atoms as well as oxidization from the MgO layers. The K u at a few-nanometer thicknesses was comparable to or higher than those reported for perpendicularly magnetized CoFeB films, which are conventionally used in MRAMs, whereas the M s value was one third or smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are promising materials because of their magnetic properties and their compatibility to the silicon process in film fabrication.