Polarization reduction in half-metallic Heusler alloys: the effect of point defects andinterfaces with semiconductors

Abstract

Half-metallic full-Heusler alloys represent a promising class of materials for spintronicapplications. However, (i) intrinsic point defects in Heusler compounds can be detrimentalwith respect to their predicted 100% spin polarization at the Fermi level and (ii) whenjoined to mainstream semiconductors the presence of interface states—whichdestroys half-metallicity—can degrade their performance. Here, we present anoverview of recent first-principles calculations performed to explore both theseissues. In particular, we focus on ab initio FLAPW calculations performed forCo2MnGe and Co2MnSi in the presence of intrinsic defects (such as stoichiometric atomic swaps as well asnon-stoichiometric antisites) and when interfaced with GaAs and Ge. Our findings showthat Mn antisites, due to their low formation energies, can easily occur, in excellentconsistency with experimental observations, and that they do not destroy half-metallicity.On the other hand, Co antisites, which also show a modest formation energy, give rise todefect states at the Fermi level. As for the [001]-ordered interfaces, we show that the stronghybridization in proximity to the junction gives rise to rather broad interfacestates that locally destroy half-metallicity. However, the bulk gaps (both in theminority spin channel for the Heusler alloy and for both spin channels in thesemiconducting side) are fully recovered within a few layers away from the junction.