Thermal Conductivity Anomalies Related to the Double-Bump of Resistivity in Nd_0.7Sr_0.3Mn_1-xCr_xO₃

The temperature dependence of the thermal conductivity k(T) and electrical resistivity ρ(T) has been measured for perovskite Nd_0.7Sr_0.3Mn_1-xCr_xO₃ (0.01≤x ≤0.15) in the temperature range of 10--300K. The double-bump feature in ρ(T) is observed for x=0.08 and 0.10 samples. Below the insulating-metallic transition temperature T_IM, k(T) shows a sharp increase and such an increase is depressed gradually by the increasing Cr content. While k(T) displays an anomalous decrease around the temperature where the second bump of ρ(T) emerges. We suggest that the enhancement of k(T) below T_IM is related to both phonons and magnons, the ferromagnetic interaction of Mn³⁺-O-Cr³⁺ should be super-exchange interaction rather than double-exchange interaction, and the Cr doping just weakens the DE interaction in this system.