Electronic structure of the magnetic halide double perovskites Cs2(Ag,Na)FeCl6 from first-principles

TL;DR

This study uses advanced DFT methods to analyze the electronic, structural, and magnetic properties of Fe-containing magnetic halide double perovskites Cs2(Ag,Na)FeCl6, revealing parameter sensitivities and effects of disordered magnetism on electronic structure.

Contribution

It provides a detailed first-principles analysis of these perovskites using improved DFT techniques, highlighting the impact of magnetic disorder and parameter choices.

Findings

Cs2AgFeCl6 and Cs2NaFeCl6 are antiferromagnets with low Néel temperatures.

Electronic structures are highly sensitive to Hubbard U and hybrid-DFT parameters.

Disordered magnetism significantly affects Cs2AgFeCl6's electronic band structure.

Abstract

A family of magnetic halide double perovskites (HDPs) have recently attracted attention due to their potential to broaden application areas of halide double perovskites into e.g. spintronics. Up to date the theoretical modelling of these systems have relied on primitive approximations to the density functional theory (DFT). In this paper, we study structural, electronic and magnetic properties of the Fe$^{3+}$-containing HDPs Cs$_2$AgFeCl$_6$ and Cs$_2$NaFeCl$_6$ using a combination of more advanced DFT-based methods, including DFT+U, hybrid-DFT and treatments of various magnetic states. We examine the effect of varying the effective Hubbard parameter, U$_{eff}$, in DFT+U and the mixing-parameter, $\alpha$, in hybrid DFT on the electronic structure and structural properties. Our results reveal a set of localized Fe(d) states that are highly sensitive to these parameters. Cs$_2$AgFeCl$_6$ and Cs$_2$NaFeCl$_6$ are both antiferromagnets with Ne\'el temperatures well below room temperature and are thus in their paramagnetic (PM) state at the external conditions relevant to most applications. Therefore, we have examined the effect of disordered magnetism on the electronic structure of these systems and find that while Cs$_2$NaFeCl$_6$ is largely unaffected, Cs$_2$AgFeCl$_6$ shows significant renormalization of its electronic band structure.