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 (TMR). 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, 450, and 550 °C. Magnetic tunnel junctions with MgO barriers and CoFe counter-electrodes were fabricated. After post-annealing at up to Ta = 425 °C negative TMR was obtained around zero bias, providing evidence for inverted spin polarization. The band structures of both electrodes were computed within the coherent potential approximation and used to calculate the TMR(V) characteristics, which were in good agreement with our experimental findings.