Exploration of trivial and non-trivial electronic phases and of collinear and non-collinear magnetic phases in low-spin d$^5$ perovskites

TL;DR

This paper investigates the diverse electronic and magnetic phases in low-spin d$^5$ perovskites, highlighting the role of spin-orbit coupling and structural distortions in stabilizing various states such as Dirac semimetals and different magnetic orders.

Contribution

It formulates a multi-band Hubbard model and performs SOC tunable DFT+$U$ calculations to identify eight possible phases in low-spin d$^5$ perovskites, extending understanding of their phase diagram.

Findings

Identification of eight electronic and magnetic phases including Dirac semimetal and insulator states.

Correlation between octahedral tilting and noncollinear magnetic ordering.

Presence of soft phase boundaries enabling phase transitions under external stimuli.

Abstract

The $4d$ and $5d$ transition metal oxides have become important members of the emerging quantum materials family due to competition between onsite Coulomb repulsion ($U$) and spin-orbit coupling (SOC). Specifically, the systems with $d^5$ electronic configuration in an octahedral environment are found to be capable of posessing invariant semimetallic state and perturbations can lead to diverse magnetic phases. In this work, by formulating a multi-band Hubbard model and performing SOC tunable DFT+$U$ calculations on a prototype SrIrO$_3$ and extending the analysis to other iso-structural and isovalent compounds, we present eight possible electronic and magnetic configurations in the $U$-SOC phase diagram that can be observed in the family of low-spin $d^5$ perovskites. They include the protected Dirac semimetal state, metal and insulator regimes, collinear and noncollinear spin ordering. The latter is explained through connecting hopping interactions to the rotation and tilting of the octahedra as observed in GdFeO$_3$. Presence of several soft phase boundaries makes the family of $d^5$ perovskites an ideal platform to study electronic and magnetic phase transitions under external stimuli.