Structural and magnetic heterogeneities, phase transitions, $^{55}$Mn NMR, and magnetoresistive properties of La$_{0.6}$Sr$_{0.3-x}$Bi$_x$Mn$_{1.1}$О$_3$

The structural, resistive, magnetic, and magnetoresistive properties of the La$_{0.6}$Sr$_{0.3-x}$Bi$_x$Mn$_{1.1}$О$_3$ ceramics have been studied. The substitution of Bi ions for Sr ions increases the lattice parameter of the rhombohedral perovskite structure, decreases the metal-semiconductor and ferromagnet-paramagnet phase transition temperatures and the peak of the magnetoresistive effect, and increases the resistivity, approaching the system to the ferroelectric state. The $^{55}$Mn NVR study indicates on the high-frequency Mn$^{3+}$ $\leftrightarrow$ Mn$^{4+}$ superexchange and heterogeneity of the valence and magnetic states of manganese due to the nonuniformity of distribution of all ions and defects. The phase diagram has been constructed, which shows a strong correlation between the structural, magnetic, and magnetoresistive properties.