Effect of carrier concentration on magnetism and magnetic order in the pyrochlore iridates

TL;DR

This study investigates how varying carrier concentration affects magnetic properties and order in pyrochlore iridates, revealing that carrier doping influences magnetic anomalies and long-range order differently.

Contribution

It provides new insights into the relationship between carrier doping and magnetic order in pyrochlore iridates, highlighting the suppression of muon precession with doping.

Findings

Magnetic anomalies occur at specific temperatures for Nd and Sm iridates.

Long-range magnetic order sets in at much lower temperatures than anomalies.

Carrier doping suppresses muon precession without affecting magnetic anomaly temperatures.

Abstract

We present resistivity, magnetization, and zero field muon spin relaxation ($\mu$SR) data for the pyrochlore iridate materials Nd$_{2-x}$Ca$_{x}$Ir$_{2}$O$_{7}$ ($x = 0, 0.06$, and $0.10$) and Sm$_2$Ir$_2$O$_7$. While Nd$_{2}$Ir$_{2}$O$_{7}$ (Nd227) is weakly conducting, Sm$_{2}$Ir$_{2}$O$_{7}$ (Sm227) has slowly diverging resistivity at low temperature. Nd227 and Sm227 exhibit magnetic anomalies at $T_{M} = 105 K$ and $137 K$, respectively. However, zero-field $\mu$SR measurements show that long-range magnetic order of the Ir$^{4+}$ sublattice sets in at much lower temperatures ($T_{LRO} \sim 8 K$ for Nd227 and $70 K$ for Sm227); both materials show heavily damped muon precession with a characteristic frequency near 9 MHz. The magnetic anomaly at $T_{M}$ in Nd227 is not significantly affected by the introduction of hole carriers by Ca-substitution in the conducting Nd$_{2-x}$Ca$_{x}$Ir$_{2}$O$_{7}$ samples, but the muon precession is fully suppressed for both.