Evaluation of Half-metallic Antiferromagnetism in ${\cal A}_2$CrFeO$_6$ ({$\cal A$}=La, Sr

TL;DR

This study uses first-principles calculations to explore the magnetic and electronic properties of double perovskites La$_2$CrFeO$_6$ and Sr$_2$CrFeO$_6$, revealing their insulating and half-metallic ferrimagnetic states, respectively, with potential for spintronic applications.

Contribution

The paper provides the first theoretical prediction of a half-metallic antiferromagnetic state in Sr$_2$CrFeO$_6$, expanding understanding of double perovskite magnetic properties.

Findings

La$_2$CrFeO$_6$ is an insulating ferrimagnet with antialigned Cr and Fe spins.

Sr$_2$CrFeO$_6$ is predicted to be a half-metallic compensated ferrimagnet.

Application of Coulomb U transforms Sr$_2$CrFeO$_6$ into a zero-moment half-metal.

Abstract

The nearly well-ordered double perovskite La$_2$CrFeO$_6$ has been synthesized recently. Contrary to previous theoretical predictions, but in agreement with experimental observations, our first principle calculations indicate an insulating ferrimagnet La$_2$CrFeO$_6$ with antialigned S=3/2 Cr$^{3+}$ and S=5/2 Fe$^{3+}$ ions,using the local spin density approximation (LSDA), a correlated band theory LDA+U, and a semilocal functional modified Becke-Johnson method. Additionally, we investigated the double perovskite Sr$_2$CrFeO$_6$, which is as yet unsynthesized. In LSDA calculations, this system shows formally tetravalent Cr and Fe ions both having antialigned $S$=1 moments, but is a simple metal. Once applying on-site Coulomb repulsion U on both Cr and Fe ions, this system becomes half-metallic and the moment of Fe is substantially reduced, resulting in zero net moment. These results are consistent with our fixed spin moment studies. Our results suggest a precisely compensated half-metallic Sr$_2$CrFeO$_6$.