Tunneling magnetoresistance in MnRuGa based Magnetic Tunnel Junctions

Nowadays great attention has been paid to the research of intermetallic Heusler compounds. These materials have widely tunable properties. They display high spin polarisation [1], low magnetic moment [2] and low Gilbert damping α [3]. Furthermore, these thin-film samples can possess huge uniaxial anisotropy fields, exceeding tens of Teslas [4]. Such a wide range of almost completely tunable properties make these materials very attractive for THz based spin-transfer-torque oscillators [6]. Here we have successfully integrated a compensated half-metallic ferrimagnet as a fixed layer in magnetic tunnel junctions (MTJ). Theoretically, this class of materials was predicted in 1995 by van Leuken and de Groot [7], but experimentally the zero-moment half-metal was realized only in 2014 [8] for a near-cubic Heusler alloy of Mn, Ru, and Ga (MRG). We showed that Tunneling Magnetoresistance (TMR) ratio reaches 40% in our stacks. We also demonstrate that the TMR exists even when the net magnetization of MRG is strictly zero, implying that, at compensation, MRG exhibits a sizable spin polarization [9]. We investigated the role of different diffusion barrier layers between MRG and the tunneling barrier as well as annealing temperature.