Ultra-Fast & Low Power STT-Switching of Ferrimagnetic Heusler Alloys for MRAM

Abstract

Today’s STT-MRAM magnetic tunnel junctions (MTJ) with conventional CoFeB magnetic electrodes suffer at high-speed operation due to the large overdrive current that is required to switch the free layer. Mn3Ge ordered Heusler alloy comprised magnetic tunnel junctions (MTJ) can be switched efficiently at high speeds, even at sub-nanosecond level, which is attributed to the low magnetic moment of the Mn3Ge ferrimagnet. At the same time, tetragonal Mn3Ge exhibits large magnetocrystalline perpendicular magnetic anisotropy. Its anisotropy and coercivity values are found to be scalable with its thickness, providing high thermal stability and high field immunity in fabricated MTJ devices. The atomically ordered Mn3Ge can be grown epitaxially on CMOS compatible, amorphous Si substrates via suitable chemical templating layers and show tunneling magnetoresistance values (TMR) of up to 69% in ultrathin films that can be switched via spin transfer torque (STT). These results demonstrate how low moment Mn3Ge MTJs requiring reduced switching currents allow for denser STT-MRAM applications.