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

The structural, resistance, magnetoresistance and dielectric properties of La
_0.7
Ca
_0.3-x
K
_x
Mn
_1+x
O
_3-δ
ceramics with a concentration of 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 ε' 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 ε' within the room temperature range is determined. Superstoichiometric manganese leads to an increase in the spin and charge polarization of the electronic subsystem.