Structural and magnetic heterogeneities, phase transitions, and magnetoresistance and magnetoresonance properties of the
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ISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Structural and Magnetic Heterogeneities, Phase Transitions, and Magnetoresistance and Magnetoresonance Properties of the Composition Ceramic La0.7Pb0.3 – xSnxMnO3 V. P. Pashchenkoa,*, A. V. Pashchenkoa, V. K. Prokopenkoa, Yu. F. Revenkoa, V. V. Burkhovetskiia, A. A. Shemyakova†, A. G. Sil’chevab, and G. G. Levchenkoa a
Galkin Institute for Physics and Engineering, National Academy of Sciences of Ukraine, Donetsk, 83114 Ukraine email: [email protected] b Luhansk Taras Shevchenko National University, Oboronnaya ul. 2, Luhansk, 91011 Ukraine Received April 12, 2011
Abstract—The La0.7Pb0.3 – xSnxMnO3 composition ceramic is studied by Xray diffraction, resistive, mag netic, electronmicroscopic, magnetoresistance, and NMR (55Mn, 139La) methods. The substitution of tin for lead results in structural phase separation into the basic perovskite ( R3c ) and spinell (Fd3m), phases: La0.7Pb0.3 – xSnxMnO3 La0.7 ⎯ xPb0.3 ⎯ xMnO3 + 0.5xLa2Sn2O7. Changes in the lattice parameter of the basic perovskite R3c 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 inplane nanostructured cluster is formed by Mn2+ ions located in distorted Apositions. The detected anomalous magnetic hysteresis is induced by the appearance of a unidirectional exchange anisotropy at the boundary of an inplane antifer romagnetic cluster coherently joined with a ferromagnetic matrix structure. The broad asymmetric NMR Mn4+ superexchange and a nonuniform dis spectra of 55Mn and 139La indicate a highfrequency Mn3+ tribution of ions and defects. The constructed phase diagram characterizes a strong relation between the magnetic and transport properties in rareearth manganites. DOI: 10.1134/S1063776112030193 †
1. INTRODUCTION
Least understood rareearth manganites doped with Pb [3, 12] and Sn [13, 14] are of particular inter est among the rareearth manganites R1 – xAxMnO3 (R = La, Pr, Nd; A = Ca, Sr, Ba, Pb) [1–5] with colos sal magnetoresistance (MR), whose nature is disput able [6–8]. These manganites are known to have a real prospect of practical application [9–11]. The small number of investigations of rareearth manganites containing Pb and Sn is related to the technological complexity of works with the oxides of these elements due to the low temperatures of their dissociation and melting and, hence, hardtocontrol composition and properties. Manganite–lanthanide perovskites La1 ⎯ xPbxMnO3 at x = 0.3 with high temperatures (more than 300 K) of metal–semiconductor (Tms) and ferromagnetic–paramagnetic (Tc) phase transitions near which an MR effect peak is detected at Tp are worthy of notice. Another original method for increas ing Tc, Tms, Tp, and the MR effect is doping with sto ichiometric manganese, which dissolves in a perovs kite structure and forms nanostructured clusters and † De
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