Compass Impurity Model of Tb Substitution in Sr2IrO4

TL;DR

This paper introduces a compass impurity model for Tb substitution in Sr2IrO4, explaining how magnetic interactions lead to vortex formation and suppression of antiferromagnetic order, with implications for double perovskites.

Contribution

It proposes a novel compass model for impurity interactions in Sr2IrO4 and suggests its realization in ordered double perovskites, advancing understanding of magnetic impurity effects.

Findings

Impurity Tb$^{4+}$ induces Ising-like bond interactions.

Magnetic vortices nucleate near impurities, disrupting order.

Reentrant transition suppresses the Néel temperature.

Abstract

We show that upon Tb substitution the interaction between the magnetic moments on the impurity Tb$^{4+}$ ion and its surrounding Ir$^{4+}$ ions is described by a "compass" model, i.e., Ising-like interaction favoring the magnetic moments across each bond to align along the bond direction. Such interaction nucleates quenched magnetic vortices near the impurities and drives a reentrant transition out of the antiferromagnetic ordered phase at low temperatures hence quickly suppresses the N\'eel temperature consistent with the experiment [Phys. Rev. B \textbf{92}, 214411 (2015)]. As a by-product, we propose that the compass model can be realized in ordered double perovskites composed of the spin-orbital-coupled $d^{5}$ ions and the half-closed-shell $f^{7}$ ions.