Role of structure imperfection in the formation of the magnetotransport properties of rare-earth manganites with a perovskite structure
The structure, the structure imperfection, and the magnetoresistance, magnetotransport, and microstructure properties of rare-earth perovskite La 0.3 Ln 0.3 Sr 0.3 Mn 1.1 O 3–δ manganites are studied by X-ray diffraction, thermogravimetry, electrical resistivity measurement, magnetic, 55 Mn NMR, mag...
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Published in | Journal of experimental and theoretical physics Vol. 124; no. 1; pp. 100 - 113 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Moscow
Pleiades Publishing
01.01.2017
Springer Springer Nature B.V |
Subjects | |
Online Access | Get full text |
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Summary: | The structure, the structure imperfection, and the magnetoresistance, magnetotransport, and microstructure properties of rare-earth perovskite La
0.3
Ln
0.3
Sr
0.3
Mn
1.1
O
3–δ
manganites are studied by X-ray diffraction, thermogravimetry, electrical resistivity measurement, magnetic,
55
Mn NMR, magnetoresistance measurement, and scanning electron microscopy. It is found that the structure imperfection increases, and the symmetry of a rhombohedrally distorted
R
3̅
c
perovskite structure changes into its pseudocubic type during isovalent substitution for Ln = La
3+
, Pr
3+
, Nd
3+
, Sm
3+
, or Eu
3+
when the ionic radius of an
A
cation decreases. Defect molar formulas are determined for a real perovskite structure, which contains anion and cation vacancies. The decrease in the temperatures of the metal–semiconductor (
T
ms
) and ferromagnet–paramagnet (
T
C
) phase transitions and the increase in electrical resistivity ρ and activation energy
E
a
with increasing serial number of Ln are caused by an increase in the concentration of vacancy point defects, which weaken the double exchange 3
d
4
(Mn
3+
)–2
p
6
(O
2–
)–3
d
3
(Mn
4+
)–
V
(
a
)
–3
d
4
(Mn
3+
). The crystal structure of the compositions with Ln = La contains nanostructured planar clusters, which induce an anomalous magnetic hysteresis at
T
= 77 K. Broad and asymmetric
55
Mn NMR spectra support the high-frequency electronic double exchange Mn
3+
(3
d
4
) ↔ O
2–
(2
p
6
) ↔ Mn
4+
(3
d
3
) and indicate a heterogeneous surrounding of manganese by other ions and vacancies. A correlation is revealed between the tunneling magnetoresistance effect and the crystallite size. A composition–structure imperfection–property experimental phase diagram is plotted. This diagram supports the conclusion about a strong influence of structure imperfection on the formation of the magnetic, magnetotransport, and magnetoresistance properties of rare-earth perovskite manganites. |
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ISSN: | 1063-7761 1090-6509 |
DOI: | 10.1134/S1063776116150127 |