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"Wigner crystal" and "stripe" models for the magnetic and crystallographic superstructures of La0.333Ca0 .667MnO3

ArXiv cond-mat/9812366 (1998)

Authors:

PG Radaelli, DE Cox, L Capogna, S-W Cheong, M Marezio

Abstract:

The crystallographic (charge-ordered) and magnetic superstructures of La0.333Ca0.667MnO3 were studied by high-resolution synchrotron x-ray and neutron powder diffraction. In the antiferromagnetic structure, which was refined using a non-collinear model, the a lattice parameter is tripled and the c lattice parameter is doubled with respect to the average crystallographic unit cell (Pnma setting). The crystallographic structure below the charge-ordering temperature (TCO ~ 260 K) is characterized by ordering of the dz2 orbitals of the Jahn-Teller-distorted Mn3+O6 octahedra in the orthorhombic ac plane, and the appearance of superlattice peaks in the x-ray patterns corresponding to a tripling of the a axis lattice parameter. The intensities of the superlattice peaks can be accounted for satisfactorily in terms of ordering of the Mn3+ cations in sites as far apart as possible in the ac plane ("Wigner crystal" model) and transverse displacements of the Mn4+O6 octahedra in the c direction. These results are not consistent with a recently proposed model based on transmission electron microscopy (TEM) data in which the Mn3+O6 octahedra are arranged in a stripe pattern ("stripe" model). In particular, the large longitudinal stripe modulation revealed by TEM is not observed, suggesting that the TEM data may not be representative of the bulk sample. Within the framework of the "Wigner crystal" model, the magnetic structure at 1.5 K and the charge-ordered superstructure at 160 K and 1.5 K were refined from the neutron data.
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Structural anomalies, oxygen ordering and superconductivity in YBa2Cu3O6+x

Chapter in Neutron scattering in layered copper-oxide superconductors, Kluwer Academic Publishers (1998) 2

Abstract:

This is the first book which reviews the most important results obtained in the past decade for layered copper-oxide high-temperature superconductors by neutron ...
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ChemInform Abstract: Neutron Diffraction Study of the Structural and Electronic Properties of Sr2HoMn2O7 and Sr2YMn2O7.

ChemInform Wiley 29:13 (1998) no-no

Authors:

PD BATTLE, JE MILLBURN, MJ ROSSEINSKY, LE SPRING, JF VENTE, PG RADAELLI
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Magnetic and Electric properties of La_{1-delta}MnO_{3}

(1998)

Authors:

S de Brion, F Ciorcas, G Chouteau, P Lejay, P Radaelli, C Chaillout
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Magnetic and Electric properties of La_{1-delta}MnO_{3}

ArXiv cond-mat/9803024 (1998)

Authors:

S de Brion, F Ciorcas, G Chouteau, P Lejay, P Radaelli, C Chaillout

Abstract:

The magnetic phase diagram of $La_{1-\delta}MnO_{3}$ powdered samples have been studied as a function of $\delta $ in the low doping range. $La_{0.97}MnO_{3}$ has a canted magnetic structure at low temperature $(\theta \simeq 130\QTR{group}{{}^{\circ}})$. Above $T_{C}=118K$, it becomes a paramagnet with a huge effective magnetic moment, $\mu_{eff}=6.0\mu_{B}$, reflecting the presence of magnetoelastic polarons which are not affected by the magnetic field (up to 20T) nor the temperature $(1.2T_{C}
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