Descrição
We have measured magnetization M (T,H), thermal conductivity κ (T,H), and thermopower S (T,H) of polycrystalline samples of Nd1-x Eux Ni O3, 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< TMI <325 K). The magnetic susceptibility (T) data, after the subtraction of the rare-earth contribution, exhibit a Curie-Weiss-like behavior at temperatures above TMI. Although a clear antiferromagnetic AF transition of the Ni sublattice is observed at TN ≤ TMI, (T) still increases down to 5 K, suggesting a heterogeneous ground state. The thermal conductivity of the NdNi O3 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 TMI and varies linearly with temperature. Below TMI, there is a minimum close to 120 K, and S (T) changes its sign at T∼30 K, indicating a competition between two types of charge carriers. A pronounced peak in S (T) at TS ∼20 K is observed and the peak remains unaltered under magnetic fields up to 90 kOe. However, its magnitude is enhanced by ∼25% with applied magnetic field, exhibiting a clear magnetothermopower effect. The combined results indicate a coexistence of ordered and disordered phases below TN and that an applied magnetic field is suitable for enhancing the thermoelectric properties close to TS. © 2007 American Institute of Physics.
