Electrical transport and magnetic properties of Nd1−xNaxMnO3 manganites

The magnetic and electrical properties of Nd1−xNaxMnO3 (x = 0, 0.1, 0.167, 0.25) are studied. A negative net magnetization is observed in the sample with x = 0. The other three samples show a ferromagnetic (FM)-insulator behavior, and intrinsic inhomogeneous magnetic characteristics are observed. Under a field of 130 kOe, the sample with x = 0.1 exhibits a sizable magnetoresistance (MR). For the samples with x = 0.167 and 0.25, there are charge ordering (CO) transitions near 250 K. The colossal magnetoresistance (CMR) effect can be understood under a percolative regime and is related to the CO-FM transition in a larger magnetic field. When the applied field is more than 30 kOe, a field-induced insulator-metal and a following metal-insulator transition at a lower temperature are observed, accompanied a thermal hysteresis.