Influence of Superstoichiometric Manganese on the Charge and Spin Polarization of Electron Subsystem of Magnetoresistance Ceramics

The structural, resistance, magnetoresistance and dielectric properties of $\mathbf{La}_{0.7}\mathbf{Ca}_{0.3-\boldsymbol{x}}\mathbf{K}_{\boldsymbol{x}}\mathbf{Mn}_{1+\boldsymbol{x}}\mathbf{O}_{3-\delta}$ ceramics with a concentration of $\boldsymbol{x}=0-0.3$ were investigated by X-ray diffraction, thermogravimetric, resistance, magnetoresistance and dielectric spectroscopy methods. It has been shown that a real perovskite structure contains variable valence of manganese ions as well as point defects of the vacancy type. It has been established that an increase in the dielectric permittivity $\varepsilon^{\prime}$ within the ultra high frequency range is observed with increase in concentration of superstoichiometric manganese in rare-earth manganites. The optimal composition of the rare-earth manganite with the high values of the magnetoresistance and $\varepsilon^{\prime}$ within the room temperature range is determined. Superstoichiometric manganese leads to an increase in the spin and charge polarization of the electronic subsystem.