Crystal structure and magnetic properties of Ba-ordered manganites Ln{sub 0.70}Ba{sub 0.30}MnO{sub 3-{delta}} (Ln = Pr, Nd)

Journal Article · Fri Sep 15 00:00:00 EDT 2006 · Journal of Experimental and Theoretical Physics

DOI:https://doi.org/10.1134/S1063776106090093· OSTI ID:21067640

Khomchenko, V A; Lobanovski, L S; Bushinsky, M V; Karpinsky, D V; Fedotova, V V; Troyanchuk, I O ^[1]; Trukhanov, A V; Stepin, S G ^[2]; Szymczak, R ^[3]; Botez, C E; Adair, A ^[4]

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1. National Academy of Sciences of Belarus, Joint Institute of Solid-State and Semiconductor Physics (Belarus)
2. Masherov State University (Belarus)
3. Polish Academy of Sciences, Institute of Physics (Poland)
4. University of Texas at El Paso (United States)

The structure and magnetic properties of the Ba-ordered state in solid solutions of manganites Ln{sub 0.70}Ba{sub 0.30}MnO{sub 3-{delta}} (Ln = Pr, Nd) with a cation ratio Ln{sup 3+}/Ba{sup 2+} >> 1 are studied experimentally. The samples are obtained by two-stage synthesis. The initial stoichiometric Ba-disordered solid solutions Ln{sub 0.70}Ba{sub 0.30}MnO{sub 3} synthesized in air according to traditional ceramic technology are characterized by the orthorhombic (Imma, Z = 4) perovskite-like unit cell and are ferromagnets with Curie temperatures T{sub C} {approx} 173 and {approx} 143 K for Pr and Nd, respectively. The average size <D> of a crystalline in the initial samples is 5 {mu}m. It is found that annealing of the initial samples in a vacuum of P[O{sub 2}] = 10{sup -4} Pa leads to their separation into three phases: (1) the anion-deficient ordered LnBaMn{sub 2}O{sub 5} phase described by a tetragonal (P4/mmm, Z = 2) perovskite-like unit cell, as well as the phases (2) Ln{sub 2}O{sub 3} (P3-barm1, Z = 1) and (3) MnO (Fm3-barm, Z = 2). Reduction leads to the formation of a nanocomposite with an average crystallite size <D> = 100 nm. Anion-deficient Ba-ordered phases of LnBaMn{sub 2}O{sub 5} exhibit ferrimagnetic properties with Neel temperatures T{sub N} {approx} 113 and {approx}123 K for Pr and Nd, respectively. Annealing of anion-deficient samples in air at a moderate temperature of T = 800{sup o}C does not change the average size of the nanocrystallite, but noticeably alters their phase composition. Stoichiometric nanocomposites consist of two perovskite-like phases: (1) the Ba-deficient ordered stoichiometric phase LnBaMn{sub 2}O{sub 6}, which is described by a tetragonal (P4/mmm, Z = 2) unit cell and has the Curie temperatures T{sub C} {approx} 313 (Pr) and {approx}303 K (Nd), and (2) the Ba-disordered superstoichiometric phase Ln{sub 0.90}Ba{sub 0.10}MnO{sub 3+{delta}}, which is described by an orthorhombic (Imma, Z = 4) unit cell and has Curie temperatures T{sub C} {approx} 138 (Pr) and {approx}123 K (Nd). The two magnetic phases of the Ba-ordered nanocomposite are exchange-coupled. For the low-temperature magnetic phase, a temperature hysteresis is observed at {delta}T {approx} 22 K in a field of 10 Oe and at {delta}T {approx} 5 K in a field of 1 kOe. It is shown that states with different degrees of ordering of cations in the A sublattice can be obtained employing different technological conditions of treatment. The significant changes in the magnetic properties of Ba-ordered nanocomposites are explained on the basis of chemical phase separation taking into account the effect of compression, which is a consequence of the action of chemical (cation ordering) and external (surface tension) pressures.

• OSTI ID: 21067640
• Journal Information: Journal of Experimental and Theoretical Physics, Vol. 103, Issue 3; Other Information: DOI: 10.1134/S1063776106090093; Copyright (c) 2006 Nauka/Interperiodica; Article Copyright (c) 2006 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-7761
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANIONS
ANNEALING
BARIUM COMPOUNDS
BARIUM IONS
CATIONS
COMPOSITE MATERIALS
CUBIC LATTICES
CURIE POINT
MAGNETIC PROPERTIES
MANGANESE OXIDES
NANOSTRUCTURES
NEEL TEMPERATURE
NEODYMIUM COMPOUNDS
NEODYMIUM IONS
ORTHORHOMBIC LATTICES
PRASEODYMIUM COMPOUNDS
PRASEODYMIUM IONS
SOLID SOLUTIONS
STOICHIOMETRY
SURFACE TENSION
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0000-0013 K
TEMPERATURE RANGE 0013-0065 K
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
TETRAGONAL LATTICES
TRIGONAL LATTICES