Role of f-d exchange interaction and Kondo scattering in Nd doped pyrochlore Iridate (Eu1-xNdx)2Ir2O7

Abstract

We report study of magnetization, resistivity, magnetoresistance and specific heat of the pyrochlore Iridate (Eu1-xNdx)2Ir2O7 with x=0.0, 0.5 and 1.0, where spin orbit coupling, electronic correlation, magnetic frustration and Kondo scattering coexists. Metal insulator transition temperature (T_MI) decrease with increase in Nd content but always coincides with magnetic irreversibility temperature (field induced moment). Resistivity below T_MI do not fit with either activated (gap) or to any power law (gapless) dependence. The Curie constant show surprising result, that Nd induces singlet correlation (reduction of para-moment) in Ir sublattice. Magnetoresistance is negative at low temperatures below 10 K and increases strongly with increase in x and vary quadratically with field switching over to linear dependence above 50 kOe. Low temperature specific heat shows Schottky peak, coming from Nd moments, showing existence of doublet split in Nd energy level, arising from f-d exchange interaction. All materials show presence of a linear specific heat in the insulating region. The coefficient of linear specific heat for x= 0.0 does not vary with external magnetic field but varies superlinearly for x = 1.0 materials. We argue that linear specific heat probably rules out weakly correlated phases like Weyl fermions. We propose that with the introduction of Nd at Eu site the system evolves from chiral spin liquid with gapless spinon excitations with a very small charge gap to Kondo type interaction superposed on chiral spin liquid coexisting with long range antiferromagnetic ordering. Huge increase of magnetoresistance with increase in Nd concentrations shows importance of Kondo scattering in the chiral spin liquid material by rare earth moments.