Negative spin polarization of Mn2VGa probed by tunnel magnetoresistance

The ferrimagnetic Heusler compound Mn2VGa is predicted to have a pseudogap in the majority spin channel, which should lead to a negative tunnel magnetoresistance. We synthesized epitaxial Mn2VGa thin films on MgO(001) substrates by dc and rf magnetron co-sputtering, resulting in nearly stoichiometric films. XRD analysis revealed a mostly B2-ordered structure for the films deposited at substrate temperatures of 350{\deg}C, 450{\deg}C, and 550{\deg}C. Magnetic tunnel junctions with MgO barrier and CoFe counter-electrodes were fabricated. After post-annealing at up to T_a=425{\deg}C negative TMR was obtained around zero bias, providing evidence for the inverted spin-polarization. Band structures of both electrodes were computed within the coherent potential approximation and used to calculate the TMR(V) characteristics, which are in good agreement with our experimental findings.