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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Abrupt jumps in the metamagnetic transitions of orbitally ordered manganites

A. Maignan, V. Hardy, C. Martin, S. Hébert, and B. Raveau

J. Appl. Phys. 93, 7361 (2003); http://dx.doi.org/10.1063/1.1543896 (3 pages) | Cited 24 times

Online Publication Date: 9 May 2003

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An experimental study of the magnetic properties of the Pr0.5Ca0.5Mn0.97Ga0.03O3 perovskite manganite is presented. The ac magnetic susceptibility measurements show that the low T orbitally and charge ordered state has been destabilized by the nonmagnetic impurity substituted for Mn. In this compound, at 2.5 K, well-defined, sharp steps on the field-dependent magnetization curves are observed. This unusual metamagnetic transition is found to be sensitive to thermal cycling. The latter induces a training effect for the transition, which strongly supports the proposed martensitic-like physics of some phase-separated manganites. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Hx Magnetic impurity interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Crystal and magnetic structure of NdBaCo2O5+δ: Spin states in a perovskite-derived, mixed-valent cobaltite

J. F. Mitchell, Jonathan Burley, and Simine Short

J. Appl. Phys. 93, 7364 (2003); http://dx.doi.org/10.1063/1.1543897 (3 pages) | Cited 17 times

Online Publication Date: 9 May 2003

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We report results of neutron powder diffraction studies on the crystallographic and magnetic structures of the compounds NdBaCo2O5+δ (δ=0.0, 0.5). Long-range antiferromagnetic order is found for the δ=0.0 compound, but no evidence of long-range charge-ordering is observed. The δ=0.5 compound shows poor long-range magnetic order, and the absence of such magnetic order is speculated to result from the particular ordered defect crystal structure of this material. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
61.66.Fn Inorganic compounds
75.50.Ee Antiferromagnetics
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena

Anomalous Hall effect and magnetoresistance in Nd1−xSrxMnO3 single crystals

H. Kuwahara, R. Kawasaki, Y. Hirobe, S. Kodama, and A. Kakishima

J. Appl. Phys. 93, 7367 (2003); http://dx.doi.org/10.1063/1.1543898 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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We have investigated Hall-effect and magnetotransport properties of Nd-based manganite crystals with controlled band filling. We have determined normal (RH) and anomalous (RS) Hall coefficients as a function of temperature in the ferromagnetic metallic crystal. The obtained effective carrier number (1/eRH) is about 1.0 hole/Mn site, which does not depend on temperature and nominal hole concentration. We have also found magnetoresistance (MR) in the over-doped samples showing various electronic, magnetic, and orbital structures. In C-type antiferromagnetic insulator (0.63⩽x), the ρ−T curve below 45 K is well explained by the variable-range hopping (VRH) mechanism. A large negative MR, which is increased with decreasing temperature, was observed in VRH region. The localization length from the characteristic temperature of VRH increases with magnetic field, which indicates that application of magnetic field induces a reduction of energy gap from EF to the mobility edge by the Zeeman shift. © 2003 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Lx Magnetic oxides
75.50.Ee Antiferromagnetics
75.47.Gk Colossal magnetoresistance
71.20.Ps Other inorganic compounds
72.20.Ee Mobility edges; hopping transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Ordering phenomena and transport properties of Bi1/2Sr1/2MnO3 single crystals

J. Hejtmánek, K. Knížek, Z. Jirák, M. Hervieu, C. Martin, M. Nevřiva, and P. Beran

J. Appl. Phys. 93, 7370 (2003); http://dx.doi.org/10.1063/1.1543911 (3 pages) | Cited 21 times

Online Publication Date: 9 May 2003

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Measurements of the electrical and thermal conductivities, thermopower, and paramagnetic susceptibility have been performed on single-crystal samples of Bi1/2Sr1/2MnO3, complemented with the x-ray powder diffraction data. A pronounced hysteretic behavior, observed below the cubic-to-orthorhombic transition at Tcrit=535 K, is related to the onset of long-range charge order (CO) at TCO=450 K and its further evolution down to about 330 K. The diffraction data suggest that the charge-ordered state is formed by Zener pairs, represented by Mn4+ dimers linked by one extra eg electron, and is possibly stabilized by cooperative Bi,Sr displacements. An extremely low thermal conductivity is observed down to the lowest temperatures, without any recovery at the antiferromagnetic ordering temperature TN=150 K. Such behavior points to a presence of strong scatterers of phonons. Their possible origin can be linked to “optical-like” oscillations that are associated with fluctuating charges within the Zener pairs. © 2003 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Ht High-field and nonlinear effects
75.20.Ck Nonmetals
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.K- Solid-solid transitions

Orbital order and anisotropic transport properties in doped manganites induced by epitaxial coherency strain

J. Klein, J. B. Philipp, D. Reisinger, M. Opel, A. Marx, A. Erb, L. Alff, and R. Gross

J. Appl. Phys. 93, 7373 (2003); http://dx.doi.org/10.1063/1.1555366 (3 pages) | Cited 17 times

Online Publication Date: 9 May 2003

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Epitaxial coherency strain is a crucial parameter strongly influencing the complex interplay between structure as well as spin, charge, and orbital degrees of freedom in the doped manganites. We have grown epitaxial manganite thin films on various substrates using ultrahigh vacuum laser molecular beam epitaxy with RHEED control. In order to study transport perpendicular to the film plane, mesa structures have been fabricated into the epitaxial films. For coherently strained La2/3Ca1/3MnO3 and La2/3Ba1/3MnO3 thin films grown on SrTiO3 and NdGaO3 substrates, an unusual transport anisotropy is observed. Whereas metallic behavior is found within the plane of biaxial coherency strain, for transport perpendicular to this plane an insulating behavior and nonlinear current–voltage characteristics are observed. This behavior can be interpreted in terms of a strain induced orbital order effect at fixed doping. Our results demonstrate the effect of epitaxial coherency strain in heterostructures required for magnetoelectronic devices. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.60.+g Mixed conductivity and conductivity transitions

Anomaly of local structure of La0.7Ca0.3−xBaxMnO3 manganites at Curie temperature

A. N. Ulyanov, Dong-Seok Yang, and Seong-Cho Yu

J. Appl. Phys. 93, 7376 (2003); http://dx.doi.org/10.1063/1.1558654 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The local structure of La0.7Ca0.3−xBaxMnO3 (x=0; 0.03; 0.06;…; and 0.3) lanthanum manganites were studied by extended x-ray absorption fine structure analysis. Dispersion, σMn�O2, and asymmetry, σMn�O3, of the pair distribution function for the Mn�O bond distances of MnO6 octahedron showed a maximum on x dependence. The maximum of σMn�O2 is caused by an increase of dynamic displacements of the Mn�O bond distances near the Curie temperature, TC. The observed x dependence of σMn�O3 is caused by a reduction in mobility of the charge carriers approaching TC from low as well as high temperatures. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.70.Dm X-ray absorption spectra
61.66.Fn Inorganic compounds
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