Metal–Insulator Transition in Pyrochlore Iridates <i>Ln</i>₂Ir₂O₇ (<i>Ln</i> = Nd, Sm, and Eu)

Abstract

We report that Ln 2 Ir 2 O 7 for Ln = Nd, Sm, and Eu have metal–insulator transitions (MITs) at 36, 117, and 120 K, respectively. Their electrical resistivities and thermoelectric powers are not discontinuous and exhibit no thermal hysteresis at their transition temperatures T MI , indicating second-order phase transitions. In this letter, we focus on the MIT of Sm 2 Ir 2 O 7 . The specific heat and the magnetic susceptibility show a clear anomaly at T MI . These results indicate that this MIT involves a magnetic ordering produced by 5 d electrons in Ir.