Insulator to Metal Transitions in Nd_0.7(Sr_0.3-yCa_y)MnO₃

Abstract

We have measured the temperature dependent resistivity of Nd_0.7(Sr_0.3-yCa_y)MnO₃ in the magnetic field up to 8 tesla, with y = 0 to 0.3 to investigate the stress-related insulator to metal (I-M) transitions. For samples with x = 0 and 0.1, the I-M transition occurs near the Curie temperature T_c, while for y = 0.2, the I-M transition temperature is much lower than T_c. No I-M transition is observed for y = 0.25 and 0.3, though there exists T_c in these two samples. Our results of the size-effect and the field dependency of the I-M transition can be explained by a combined action of the spin-dependent potential fluctuation and the magnetic interaction of the conduction electron with the localized spins.