J. Appl. Cryst.の発刊に際して

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

WinPLOTR is a graphic program for the analysis of powder diffraction patterns. It has been developed for a Windows 9x/2k/NT environment. It takes advantage of this graphical environment to offer a powerful and user-friendly powder diffraction tool. The program is able to display and analyse many different kinds of diffraction patterns as well as calculated and observed profiles coming from the Windows/DOS version of the program FullProf. It can also be used as a Graphic User Interface (GUI) for programs defined by the user.

https://www.cdifx.univ-rennes1.fr/fps/winplotr_epdic.pdf

WinPLOTR: A Windows Tool for Powder Diffraction Pattern Analysis

Solid oxide fuel cells (SOFCs) have the promise to improve energy efficiency and to provide society with a clean energy producing technology. The high temperature of operation (500−1000 °C) enables the solid oxide fuel cell to operate with existing fossil fuels and to be efficiently coupled with turbines to give very high efficiency conversion of fuels to electricity. Solid oxide fuel cells are complex electrochemical devices that contain three basic components, a porous anode, an electrolyte membrane, and a porous cathode. In this short review, a survey of the types and properties of materials that have been considered for each of these components is presented with an emphasis on the requirements for operation at intermediate temperature (500−800 °C). Some directions for future research are discussed.

Materials for Solid Oxide Fuel Cells

Colossal magnetoresistance (CMR) phenomena are observed in the perovskite-type hole-doped manganites in which the double-exchange ferromagnetic metal phase and the charge–orbital ordered antiferromagnetic phase compete with each other. The quenched disorder arising from the inherent chemical randomness or the intentional impurity doping may cause major modifications in the electronic phase diagram as well as in the magnetoelectronic properties near the bicritical point that is formed by such a competition of the two phases. One is the phase separation phenomenon on various time-scales (from static to dynamic) and on various length-scales (from glass-like nano to grain-like micron). The other is the enhanced phase fluctuation with anomalous reduction in the transition temperatures of the competing phases (and hence in the bicritical-point temperature). The highly effective suppression of such a phase fluctuation by an external magnetic field is assigned here to the most essential ingredient of the CMR physics. Such profound and dramatic features as appearing in the bicritical region are extensively discussed in this paper with ample examples of the material systems specially designed for this purpose. The unconventional phase-controls over the competing phases in terms of magnetic/electric fields and photo-excitations are also exemplified.

https://iopscience.iop.org/article/10.1088/0034-4885/69/3/R06/pdf

Critical features of colossal magnetoresistive manganites

The crystal and magnetic structures of ${\mathrm{LaTiO}}_{3}$ have been studied by x-ray and neutron-diffraction techniques using nearly stoichiometric samples. We find a strong structural anomaly near the antiferromagnetic ordering ${T}_{N}=146\mathrm{K}.$ In addition, the octahedra in ${\mathrm{LaTiO}}_{3}$ exhibit an intrinsic distortion, which implies a splitting of the ${t}_{2g}$ levels. Our results indicate that ${\mathrm{LaTiO}}_{3}$ should be considered as a Jahn-Teller system where the structural distortion and the resulting level splitting are enhanced by the magnetic ordering.

https://arxiv.org/pdf/cond-mat/0302087.pdf

Crystal and magnetic structure of LaTiO 3 : Evidence for nondegenerate t 2 g orbitals

Magnetism and charge ordering in Pr 0.5 Ca x Sr 0.5 − x MnO 3 ( x = 0.09 and 0 . 5 )

Structural transitions in the manganite Pr0.5Sr0.5MnO3

A detailed analysis of the crystal structure in $R\mathrm{Ti}{\mathrm{O}}_{3}$ with $R=\mathrm{La}$, Nd, Sm, Gd, and Y reveals an intrinsic coupling between orbital degrees of freedom and the lattice which cannot be fully attributed to the structural deformation arising from bond-length mismatch. The $\mathrm{Ti}{\mathrm{O}}_{6}$ octahedra in this series are all irregular with the shape of the distortion depending on the rare-earth ionic radius. These octahedron distortions vary more strongly with temperature than the tilt and rotation angles. Around the Ti magnetic ordering all compounds exhibit strong anomalies in the thermal-expansion coefficients, these anomalies exhibiting opposite signs for antiferromagnetic and ferromagnetic compounds. Furthermore, the strongest effects are observed in materials close to the magnetic crossover from antiferromagnetic to ferromagnetic order.

https://arxiv.org/pdf/cond-mat/0701452.pdf

Françoise Bourée

Papers

Crystal and magnetic structure of LaTiO 3 : Evidence for nondegenerate t 2 g orbitals

Magnetism and charge ordering in Pr 0.5 Ca x Sr 0.5 − x MnO 3 ( x = 0.09 and 0 . 5 )

Structural transitions in the manganite Pr0.5Sr0.5MnO3

Magnetoelastic coupling in R Ti O 3 ( R = La , Nd , Sm , Gd , Y ) investigated with diffraction techniques and thermal expansion measurements

Crystal and magnetic structure of YBaCuFeO5