Electric field induced tunable half-metallicity in an A-type antiferromagnetic bilayer LaBr2

How to achieve half-metallicity is always a central topic in spintronics and the polarity-tunable half-metallicity is particularly interesting for spin manipulation. In this work, motivated by the intrinsic ferromagnetism in the monolayer electride ${\mathrm{LaBr}}_{2}$, based on density functional theory calculations, we investigate the electronic and magnetic properties of bilayer ${\mathrm{LaBr}}_{2}$, with an aim to search for polarity-tunable half-metallicity. We first find that the antiferromagnetic interlayer coupling state is the ground state and the band structure is spin degenerate, with an indirect band gap of 0.454 eV. By applying a vertical electric field, spin splitting occurs and when the electric field is strong enough ($\ensuremath{\ge}0.33$ V/\AA{}), half-metallicity can be achieved. More interestingly, the spin polarity of the half-metallicity can be tuned by reversing the electric field direction. It originates from the spatial separation of the two spin channels in both the valence band and conduction band and their localization at different layers. Based on the polarity-tunable half-metallicity under vertical electric field, a magnetic tunnel junction based on bilayer ${\mathrm{LaBr}}_{2}$ is designed and the ON/OFF switching can be achived by applying parallel or anti-parallel vertical electric fields in the two leads, which leads to giant tunnel magnetoresistance up to $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The findings suggest new potential of ${\mathrm{LaBr}}_{2}$, and more generally, $A$-type antiferromagnets of application in spintronic devices.