Magnetic and transport properties in pyrochlore iridates (Y$_{1-x}$Pr$_x$)$_2$Ir$_2$O$_7$: The role of $f$-$d$ exchange interaction and $d$-$p$ orbital hybridization

Abstract

The f -d magnetic exchange interaction is considered to be a key ingredient for many exotic topological phases in pyrochlore iridates. Here, we have investigated the evolution of structural, magnetic and electronic properties in doped pyrochlore iridate, (Y1−xPrx)2Ir2O7. Apart from geometrical frustration, pyrochlore iridates are well known for its active spin-orbit coupling effect. The substitution of Pr 3+ (4f 2 ) for the nonmagnetic Y 3+ (4d 0 ) acts as a magnetic doping, which provides an ideal platform to study f -d exchange interaction without altering the Ir-sublattice. With Pr substitution, system retains its original cubic structural symmetry but the local structural parameters show an evolution with the doping concentration x. The robust magnetic-insulating state in Y2Ir2O7 is drastically weakened, while Pr2Ir2O7 (x = 1.0) shows a paramagnetic-metallic behavior. A metal-insulator transition is observed for x = 0.8 sample. This evolution of magnetic and electronic properties are believed to be induced by an exchange interaction between localized Pr-4f and itinerant Ir-5d electrons as well as by an increased hybridization between Ir-t2g and (basal) O-p orbitals as observed in XAS study. The resistivity in insulating materials follows a power-law behavior with a decreasing exponent with x. A negative magnetoresistance is observed for present series of samples at low temperature and where the magnetoresistance shows a quadratic field dependence at higher fields.