Thermal hysteresis in electrical transport of charge ordered La0.5Ca0.5MnO3 manganites

We synthesized charge ordered La0.5Ca0.5MnO3 manganites by conventional solid-state route, which crystallizes in single-phase form having orthorhombic structure with Pbnm space group. The electrical transport of the compound exhibits highly semi-conducting behaviour from 300 K down to 130 K and showed an insulator-metal transition (T-MI) with a sharp peak in rho(T). The low temperature resistance below 30 K exhibits some upturn in the rho(T). The charge ordered state (CO) of the Mn3+/Mn4+ ions is not clearly seen as a step in rho(T) but the same could be seen as a change in the slope of M(T) curve around charge ordered temperature(T-CO). Interestingly, when the sample is cycled for the resistance (R) measurements during cooling/heating process hysteresis of 12 K is seen near T-MI. The magneto-transport of the synthesized compound in 7T field, exhibits nearly 100% magnetoresistance (MR) between T-MI and T-CO. The fixed temperature (400, 300, 200, 130, 100 and 5 K) MR in +/- 7T field exhibited up and down cusps at all the studied temperatures. The electrical transport, large hysteresis in rho(T) and MR results can be explained in terms of complex phase separated magnetic structure of this compound around T-MI. (C) 2008 Elsevier B.V. All rights reserved.