Half-metallic monolayer superlattices with no net magnetization

Abstract

We propose a viable approach to artificial half-metallic antiferromagnets (HM-AFMs) with no spontaneous magnetization (or fully compensated ferrimagnets) through introduction of compositional periodicity into a tetrahedrally coordinated magnetic compound, which consists of alternating monolayers of transition-metal chalcogenides: $TX/MX$ ($X=\text{S}$, Se, and Te). By using a full-potential augmented plane-wave plus local-orbitals method within density-functional theory, we find two promising series of monolayer superlattices (MSLs), $\text{Cr}X/\text{Fe}X$ and $\text{V}X/\text{Co}X$, where two constituent magnetic ions in a supercell have antialigned local moments that exactly cancel by virtue of the integer filling of one spin channel. All of these MSLs with [001] orientation are predicted to be bulk HM-AFMs, whereas CrS/FeS and CrSe/FeSe are the only systems that show half-metallicity among MSLs with [111] orientation. Spin-orbit coupling of spin-polarized conduction electrons can be neglected and never destroy the half-metallicity. The relation between bonding nature and magnetic interaction is discussed in terms of the ``ghost-bond-orbital model''; the coexisting covalency in $T\text{\ensuremath{-}}X$ bonds and ionicity in $M\text{\ensuremath{-}}X$ bonds would stabilize and enhance the ferromagnetic double exchange and antiferromagnetic superexchange interactions within each local bond, respectively, realizing the half-metallic antiferromagnetism of the $TX/MX$ systems.