The effect of replacement of Mn ions by Fe ions on the metal-semiconductor transition in manganites

We study the electrical resistance $\rho$, the thermoelectric force $\alpha$, the magnetoresistance $\Delta\rho/\rho$, the spontaneous magnetization $\sigma_s$ and the Curie temperature $Т_c$ of monocrystalline manganites $La_{0,6}Pb_{0,4}Fe_yMn_{1-y}O_3$ for y = 0; 0.10; 0.15, and 0.22 in the temperature range from 80 to 800 K and in magnetic fields up to 14 kOe. It is established that the manganites under study are magnetic semiconductors whose width of the forbidden gap is, in order of magnitude, comparable with the energy of the exchange interaction. This causes a metal-semiconductor transition in the neighborhood of the Curie temperature. The replacement of Mn ions by the Fe ions leads to an increase of $\rho$ and of the activation energy $\Delta E$, and to a decrease of the Curie temperature $Т_c$ and of the spontaneous magnetization.