Effects of Fe doping on the thermal hysteresis of the La0.5Ca0.5MnO3 system

Abstract

A series of polycrystalline La_0.5Ca_0.5Mn_1−xFe_xO₃ (x = 0.010, 0.025, 0.050, 0.075, 0.100, 0.125, 0.150, 0.175 and 0.200) was synthesized using a solid state reaction. We investigated the electrical resistivity, thermopower, and magnetization as a function of temperature. La_0.5Ca_0.5MnO₃ exhibits a large thermal hysteresis in its electrical resistivity, thermopower, and magnetization, which can be attributed to the charge density waves pinned by impurities. The thermal hysteresis decreases with increasing Fe content up to x = 0.050 and disappears at even higher x. La_0.5Ca_0.5MnO₃ shows nonmetal-like behavior in terms of its electrical resistivity within the entire investigated temperature range of 80–300 K, while the x = 0.010 and 0.025 samples show metal–nonmetal transitions in their electrical resistivity at about 137–149 K. The metal–nonmetal transition can be attributed to the reduction of charge ordering at small Fe content values. However, there is no metal–nonmetal transition observed for x ≥ 0.050, which arises from the suppression of the double exchange mechanism at high Fe content values. The activation energy derived from electrical resistivity differs from that derived from thermopower, indicating that the conduction mechanism is polaronic transport in La_0.5Ca_0.5Mn_1−xFe_xO₃. The magnetic transition temperature is observed at ∼168 K and ∼135 K for x = 0.010 and 0.025, respectively. There is no magnetic transition observed for x = 0.100 and 0.200.