Magnetothermopower in Nd1-xEuxNiO3 compounds

摘要

We have measured magnetization M(T,H), thermal conductivity kappa(T,H), and thermopower S(T,H) of polycrystalline samples of Nd1-xEuxNiO3, 0 <= x <= 0.35, as a function of temperature and external magnetic field. The data indicate a metal-insulator (MI) transition in a wide range of temperature (200 < T-MI < 325 K). The magnetic susceptibility chi(T) data, after the subtraction of the rare-earth contribution, exhibit a Curie-Weiss-like behavior at temperatures above T-MI. Although a clear antiferromagnetic AF transition of the Ni sublattice is observed at T-N <= T-MI, chi(T) still increases down to 5 K, suggesting a heterogeneous ground state. The thermal conductivity of the NdNiO3 compound is not affected by an external magnetic field of 90 kOe in a wide range of temperature, and its temperature dependence below 15 K is approximately quadratic, strongly suggesting the presence of disorder. S(T) is negative above T-MI and varies linearly with temperature. Below T-MI, there is a minimum close to 120 K, and S(T) changes its sign at T similar to 30 K, indicating a competition between two types of charge carriers. A pronounced peak in S(T) at T-S similar to 20 K is observed and the peak remains unaltered under magnetic fields up to 90 kOe. However, its magnitude is enhanced by similar to 25 with applied magnetic field, exhibiting a clear magnetothermopower effect. The combined results indicate a coexistence of ordered and disordered phases below T-N and that an applied magnetic field is suitable for enhancing the thermoelectric properties close to T-S. (c) 2007 American Institute of Physics.