Spontaneous Hall Effect enhanced by local Ir moments in epitaxial Pr$_2$Ir$_2$O$_7$ thin films

TL;DR

This study demonstrates an elevated-temperature spontaneous Hall effect in epitaxial Pr2Ir2O7 thin films, attributed to localized Ir moments and lattice distortions, revealing topological phenomena in frustrated magnetic materials.

Contribution

The paper reports the observation of a spontaneous Hall effect at higher temperatures in thin films, linking it to Ir local moments and lattice distortions, expanding understanding of topological effects in pyrochlore iridates.

Findings

Spontaneous Hall effect observed up to 15K in thin films.

Ir local moments linked to lattice distortions absent in bulk.

Topological origin of Hall effect suggested by lack of long-range magnetic order.

Abstract

Rare earth pyrochlore Iridates (RE2Ir2O7) consist of two interpenetrating cation sublattices, the RE with highly-frustrated magnetic moments, and the Iridium with extended conduction orbitals significantly mixed by spin-orbit interactions. The coexistence and coupling of these two sublattices create a landscape for discovery and manipulation of quantum phenomena such as the topological Hall effect, massless conduction bands, and quantum criticality. Thin films allow extended control of the material system via symmetry-lowering effects such as strain. While bulk Pr2Ir2O7 shows a spontaneous hysteretic Hall effect below 1.5K, we observe the effect at elevated temperatures up to 15K in epitaxial thin films on (111) YSZ substrates synthesized via solid phase epitaxy. Similar to the bulk, the lack of observable long-range magnetic order in the thin films points to a topological origin. We use synchrotron-based element-specific x-ray diffraction (XRD) and x-ray magnetic circular dichroism (XMCD) to compare powders and thin films to attribute the spontaneous Hall effect in the films to localization of the Ir moments. We link the thin film Ir local moments to lattice distortions absent in the bulk-like powders. We conclude that the elevated-temperature spontaneous Hall effect is caused by the topological effect originating either from the Ir or Pr sublattice, with interaction strength enhanced by the Ir local moments. This spontaneous Hall effect with weak net moment highlights the effect of vanishingly small lattice distortions as a means to discover topological phenomena in metallic frustrated magnetic materials.