First-principles evidence of Mn moment canting in hole-dopedBa1−2xK2xMn2As2

Abstract

The compound BaFe${}_{2}$As${}_{2}$ is the proptotypical example of the 122 family of high-${T}_{c}$ Fe-based superconductors that crystallize in the ThCr${}_{2}$Si${}_{2}$ structure. Isostructural compounds can be formed by replacing Fe with another transition metal; using Mn produces the material BaMn${}_{2}$As${}_{2}$, which unlike its Fe-based cousin has an insulating ground state with a large magnetic moment of $3.9\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$ and G-type antiferromagnetic order. Despite its lack of superconductivity, the material is interesting in its own right. Recent experimental studies have shown that hole doping the compound by substituting K for Ba leads to metallic behavior and a spontaneous, weak, in-plane magnetization, which was attributed to the holes fully polarizing independent of the Mn moments, producing half-metallic behavior. However, the observed in-plane magnetization can also be understood as a small canting of the Mn moments. Using density functional theory, we demonstrate that a Mn moment canting occurs upon hole doping the compound. We argue that this is due to the competition between the super- and double-exchange interactions, which we support using a simple tight-binding model of the superexchange--double-exchange interaction and the Andersen force theorem. Our calculations also rule out an in-plane polarization of As holes as an explanation for the in-plane magnetization.