Ferroelectrically induced half-metallicity, giant tunnel electroresistance, and giant tunnel magnetoresistance in spin-semiconducting <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>LaBr</mml:mi><mml:mn>2</mml:mn></mml:msub

Half-metallicity is very important in spintronics due to its ability to realize fully spin polarized transport. Due to the rise of two-dimensional (2D) materials, how to achieve half-metallicity in 2D materials has attracted great attention in recent years and various schemes have been proposed for this goal in intrinsically non-half-metallic magnetic systems, whereas these schemes are primarily limited to antiferromagnetic systems. It is desirable and significant to turn ferromagnets into half-metals. In this work, by taking magnetic ${\mathrm{LaBr}}_{2}$ monolayer as an example, based on density functional theory calculations, we propose a scheme to achieve half-metallicity in a kind of ferromagnetic systems called spin semiconductors by forming a van der Waals (vdW) heterostructure with a 2D ferroelectric material $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. It is found that not only half-metallicity can be achieved in ${\mathrm{LaBr}}_{2}$, but it can also switch between half-metal and semiconductor accompanying with ferroelectric polarization reversal under the external electric field. The switching is interpreted by the interlayer charge transfer due to the appropriate work function differences between the contacted two surfaces. Further the obtained extremely high spin polarization (99.94%), tunnel electroresistance ratio ($2.11\ifmmode\times\else\texttimes\fi{}{10}^{5}%$), and tunnel magnetoresistance ratio ($1.62\ifmmode\times\else\texttimes\fi{}{10}^{4}%$) in the subsequent transport study of the multiferroic tunnel junction constructed with ${\mathrm{LaBr}}_{2}/\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ vdW heterostructure demonstrates that this provides a novel scheme for the new multifunctional applications of spin semiconductors such as ${\mathrm{LaBr}}_{2}$, either as a spin filter generator, or as a building block of data storage units based on giant tunnel electroresistance effect or giant tunnel magnetoresistance effect.