Energetic stability and magnetic coupling in (Cr1−xFex)2O3: Evidence for a ferrimagnetic ilmenite-type superlattice from first principles

Abstract

Based on density functional theory (DFT) calculations with a Hubbard $U$-term, we explore the possibility to design an artificial ferrimagnet FeCrO${}_{3}$ of ilmenite type out of the two antiferromagnets $\ensuremath{\alpha}$-${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ and $\ensuremath{\alpha}$-${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. By varying the concentration of Fe in $\ensuremath{\alpha}$-Cr${}_{2}$O${}_{3}$, we provide a phase diagram of the relative stability of different chemical and magnetic arrangements with respect to the end members. At $50%$ Fe-doped $\ensuremath{\alpha}$-Cr${}_{2}$O${}_{3}$, the ilmenite-like structure with alternating Fe and Cr layers and antiparallel magnetic moments competes energetically with a phase-separated structure containing a mixed Fe-Cr interface layer. The magnetic interaction parameters between Fe($3{d}^{5}$) and Cr($3{d}^{3}$) ions in the digital ferrimagnetic heterostructure, extracted by mapping the DFT total energies to a Heisenberg Hamiltonian, indicate a hematite-like magnetic order with parallel intralayer and antiparallel interlayer alignment.