Temperature evolution of magnetic and transport behavior in 5\textit{d} Mott insulator Sr$_2$IrO$_4$: Significance of magneto-structural coupling

TL;DR

This study explores how temperature influences magnetic and structural properties in Sr$_2$IrO$_4$, revealing magneto-structural coupling effects, changes in magnetic moments, and variable-range hopping conduction mechanisms.

Contribution

It uncovers the significance of magneto-structural coupling and identifies multiple VRH regimes in Sr$_2$IrO$_4$, highlighting the interplay between structure, magnetism, and electronic transport.

Findings

Structural parameters change around 100 K affecting magnetism.

Resistivity follows Mott's VRH with three temperature-dependent regimes.

Negative magnetoresistance suggests quantum interference effects.

Abstract

We have investigated the temperature evolution of magnetism and its interrelation with structural parameters in perovskite-based layered compound Sr$_2$IrO$_4$, which is believed to be a $J_{eff}$ = 1/2 Mott insulator. The structural distortion plays an important role in this material which induces a weak ferromagnetism in otherwise antiferromagnetically ordered magnetic state with transition temperature around 240 K. Interestingly, at low temperature below around 100 K, a change in magnetic moment has been observed. Temperature dependent x-ray diffraction measurements show sudden changes in structural parameters around 100 K are responsible for this. Resistivity measurements show insulating behavior throughout the temperature range across the magnetic phase transition. The electronic transport can be described with Mott's two-dimensional variable range hopping (VRH) mechanism, however, three different temperature ranges are found for VRH, which is a result of varying localization length with temperature. A negative magnetoresistance (MR) has been observed at all temperatures in contrast to positive behavior generally observed in strongly spin-orbit coupled materials. The quadratic field dependence of MR implies a relevance of a quantum interference effect.