Structural and magnetic heterogeneities, phase transitions, and magnetoresistance and magnetoresonance properties of the composition ceramic [La.sub.0.7][Pb.sub.0.3-x][Sn.sub.x]Mn[O.sub.3]

• Published in: Journal of experimental and theoretical physics Vol. 114; no. 3; pp. 503 - 1005
• Main Authors: Pashchenko, V.P, Pashchenko, A.V, Prokopenko, V.K, Revenko, Yu.F, Burkhovetskii, V.V, Shemyakov, A.A, Silcheva, A.G, Levchenko, G.G
• Format: Journal Article
• Language: English
• Published: Springer 01-03-2012
• Subjects: Analysis; Diffraction; Ferromagnetism; Perovskite; Spinel group; X-rays
• ISSN: 1063-7761; 1090-6509
• DOI: 10.1134/S1063776112030193

The [La.sub.0.7][Pb.sub.0.3 - x] Mn[O.sub.3] 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.3]c) and spinell (Fd3m), phases: [La.sub.0.7][Pb.sub.0.3 - x] Mn[O.sub.3] [right arrow] [La.sub.0.7][Pb.sub.0.3 - x] Mn[O.sub.3] + 0.5x[La.sub.2][Sn.sub.2][O.sub.7]. Changes in the lattice parameter of the basic perovskite R[bar.3]c 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 [Mn.sup.3+]/[Mn.sup.4+] ratio, and the imperfection of vacancy and cluster types. An in-plane nanostructured cluster is formed by [Mn.sub.2+] 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 antiferromagnetic cluster coherently joined with a ferromagnetic matrix structure. The broad asymmetric NMR spectra of [sup.55]Mn and [sup.139]La indicate a high-frequency [Mn.sup.3+] [left and right arrow] [Mn.sup.4+] 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.