Mapping the structural, magnetic and electronic behavior of (Eu$_{1-x}$Ca$_{x}$)$_{2}$Ir$_{2}$O$_{7}$ across a metal-insulator transition

TL;DR

This study maps how Ca-doping affects the structural, magnetic, and electronic properties of (Eu$_{1-x}$Ca$_{x}$)$_{2}$Ir$_{2}$O$_{7}$, revealing a decoupling of magnetic order from the metal-insulator transition and evidence of electronic phase separation.

Contribution

It provides detailed insights into the phase separation and magnetic behavior in doped iridates, highlighting the role of synthesis and rare earth magnetism.

Findings

Metal-insulator transition temperature decreases with Ca-doping.

Magnetic order persists into the metallic regime, decoupled from the MIT.

Electronic phase separation occurs without chemical segregation or symmetry change.

Abstract

In this study, we employ bulk electronic properties characterization and x-ray scattering/spectroscopy techniques to map the structural, magnetic and electronic properties of (Eu$_{1-x}$Ca$_{x}$)$_{2}$Ir$_{2}$O$_{7}$ as a function of Ca-doping. As expected, the metal-insulator transition temperature, $T_{MIT}$, decreases with Ca-doping until a metallic state is realized down to 2 K. In contrast, $T_{AFM}$ becomes decoupled from the MIT and (likely short-range) AFM order persists into the metallic regime. This decoupling is understood as a result of the onset of an electronically phase separated state, the occurrence of which seemingly depends on both synthesis method and rare earth site magnetism. PDF analysis suggests that electronic phase separation occurs without accompanying chemical phase segregation or changes in the short-range crystallographic symmetry while synchrotron x-ray diffraction confirms that there is no change in the long-range crystallographic symmetry. X-ray absorption measurements confirm the $J_{eff}$ = 1/2 character of (Eu$_{1-x}$Ca$_{x}$)$_{2}$Ir$_{2}$O$_{7}$. Surprisingly these measurements also indicate a net electron doping, rather than the expected hole doping, indicating a compensatory mechanism. Lastly, XMCD measurements show a weak Ir magnetic polarization that is largely unaffected by Ca-doping.