paper

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

arXiv:1406.0194

Abstract

We present resistivity, magnetization, and zero field muon spin relaxation ( $I^¼$ 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 $I^¼$ SR measurements show that long-range magnetic order of the Ir $^{4 +}$ sublattice sets in at much lower temperatures ( $T_{L R O} \sim 8 K$ 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.