The transport, magnetic properties for Zn-doped La 2CuO 4+ y and the cooling rate effect

Abstract

We report a study on the temperature dependence of thermoelectric power, dc susceptibility, and resistivity of Zn-doped La 2CuO 4+ y with changing cooling rates from 330 K. The antiferromagnetic (AF) transition temperature T N is not changed with changing cooling rates. By contrast, there is a big influence on the thermopower (below 275 K) and the resistivity (above 125 K) by changing cooling rates. The high-temperature thermopower is weakly temperature dependent, suggesting a hopping contribution of polaron. The change of cooling rates does not change the charge carrier concentration. Quenching apparently decreases the temperature T drop corresponding to the kink in the thermopower. It is confirmed that the T drop is not related to the AF transition. We attribute the polaron band contribution to the linear decrease in the thermopower below T drop. The spinodal in thermopower at low temperature is proved to be related to the occurrence of the two-dimensional variable range hopping.