Negative spin polarization of Mn2VGa probed by tunnel magnetoresistance

TL;DR

This study demonstrates negative tunnel magnetoresistance in epitaxial Mn2VGa thin films, confirming the predicted inverted spin polarization due to a pseudogap in the majority spin channel, through experimental and theoretical analysis.

Contribution

First experimental observation of negative TMR in Mn2VGa films, validating theoretical predictions of inverted spin polarization in this Heusler compound.

Findings

Negative TMR observed around zero bias after annealing.

Band structure calculations agree with experimental TMR(V) characteristics.

Epitaxial Mn2VGa films exhibit B2-ordered structure at various substrate temperatures.

Abstract

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.