Structural and magnetic heterogeneities, phase transitions, and magnetoresistance and magnetoresonance properties of the composition ceramic La0.7Pb0.3 − xSnxMnO3

The La0.7Pb0.3 − xSnxMnO3 composition ceramic is studied by X-ray diffraction, resistive, magnetic, electron-microscopic, magnetoresistance, and NMR (55Mn, 139La) methods. The substitution of tin for lead results in structural phase separation into the basic perovskite (\(R\bar 3c\)) and spinell (Fd3m), phases: La0.7Pb0.3 − xSnxMnO3 → La0.7 − xPb0.3 − xMnO3 + 0.5xLa2Sn2O7. Changes in the lattice parameter of the basic perovskite \(R\bar 3c\) structure, the electrical resistivity, and the magnetic and magnetoresistance properties are caused by changes in the composition and content of a conducting perovskite ferromagnetic phase, the Mn3+/Mn4+ ratio, and the imperfection of vacancy and cluster types. An in-plane nanostructured cluster is formed by Mn2+ ions located in distorted A-positions. The detected anomalous magnetic hysteresis is induced by the appearance of a unidirectional exchange anisotropy at the boundary of an in-plane antifer-romagnetic cluster coherently joined with a ferromagnetic matrix structure. The broad asymmetric NMR spectra of 55Mn and 139La indicate a high-frequency Mn3+ ↔ Mn4+ superexchange and a nonuniform distribution of ions and defects. The constructed phase diagram characterizes a strong relation between the magnetic and transport properties in rare-earth manganites.