Semiconducting and magnetic properties of La0.67Ca0.33Mn1-xDyxO3 ceramics

Electrical resistivity measurements of La_0.67Ca_0.33Mn_1-xDy_xO₃ , x=0 to 0.12, ceramics have been studied using a standard four point probe technique, while the magnetic behaviour has been studied using AC susceptibility techniques. The transport properties show the transition from semiconducting to metallic conductivity at T_p and paramagnetic-ferromagnetic transitions, T_c, were observed in the χ-temperature curves for all samples. The existence of metallic conductivity, T_p, and ferromagnetism, T_c, were found to be linearly correlated. This phenomenon of coexistence is due to the double exchange interaction of two electrons in Mn³⁺ -O^2--Mn⁴⁺ and Mn⁴⁺-O^2--Mn³⁺ configuration which brings the system below T_c into a metallic state. Hence, it is observed that the Curie temperature T_c is closely related to the sharp decrease in electrical resistivity of the samples. However, both transition temperatures shift to lower temperatures as dysprosium doping increases, indicating the loss of ferromagnetic order and transport properties. As for the transport properties, the semiconductor model ln(σ)~(E_g/2kT) was used to explain the conduction mechanism of perovskite manganites above T_p. It was concluded that the total conductivity σ_tot consists of the intrinsic and extrinsic components such that σ_tot=σ_int+σ_ext. The energy gap decreases initially from 0.11 eV to a minimum value of 0.06 eV at x=0.03 and increases again to 0.08 eV at the composition of x=0.12 for the extrinsic region