Structural and magnetic heterogeneities, phase transitions, and magnetoresistance and magnetoresonance properties of the composition ceramic La0.7Pb0.3 − x Sn x MnO3

The La0.7Pb0.3 − x Sn x MnO3 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 − x Sn x MnO3 → La0.7 − x Pb0.3 − x MnO3 + 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.