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Neutron Diffraction (neutron + diffraction)
Kinds of Neutron Diffraction Terms modified by Neutron Diffraction Selected AbstractsIn Situ Characterization of a Nb and Mo Containing , -TiAl Based Alloy Using Neutron Diffraction and High-Temperature Microscopy,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Ian J. Watson Abstract In recent times, novel titanium aluminides containing the bcc , -phase at high temperatures are being developed for improved hot-working capabilities, however, predictions of the phase diagrams are merely uncertain. Here we present in-situ neutron studies, which are particularly sensitive to the atomic disorder in the ordered phases. Complementary laser scanning confocal microscopy is employed for in-situ microstructural investigations. [source] Neutron Diffraction of Zirconia-Dispersed Alumina with Increasing Stress and TemperatureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Geoffrey A. Carter Neutron and X-ray diffraction were used to investigate changes in the phase composition and lattice parameters with temperature and pressure of a 20-wt% zirconia-dispersed alumina composite. Neutron diffraction was used to determine the variation of tetragonal/monoclinic zirconia phase abundance for the bulk with stress. The bulk tetragonal/monoclinic ratio decreased by 40% for a stress of 550 MPa. A difference in the tetragonal/monoclinic ratio between the near-surface and the bulk of the processed samples is believed to contribute to observed variations in nonuniform strain in the matrix, which has the effect of prestressing the sample. Placing a stress on the sample initially releases this prestressing. [source] Dispersion-Driven Hydrogen Bonding: Predicted Hydrogen Bond between Water and Platinum(II) Identified by Neutron Diffraction,ANGEWANDTE CHEMIE, Issue 41 2010Dr. Silvia Rizzato Klassisch oder nicht? Die Metallionen quadratisch-planar koordinierter d8 -Komplexe können als Lewis-Säuren oder -Basen mit H2O-Molekülen in axialen Positionen wechselwirken. Ab-initio-Rechnungen zufolge bilden neutrale PtII -Komplexe Wasserstoffbrücken mit H2O, in denen PtII als Lewis-Base auftritt. Solche nichtklassischen OH,,,Pt-Brücken wurden nun in Kristallen von trans -[PtCl2(NH3)(N -Glycin)],H2O mithilfe von Neutronenbeugung identifiziert. [source] Synthesis and Characterization of the Oxynitride Y2Mo2O4.5N2.5 Pyrochlore: A Neutron Diffraction and Magnetic Study.CHEMINFORM, Issue 21 2006M. J. Martinez-Lope Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] High- and Low-Temperature La2RuO5 by Powder Neutron Diffraction.CHEMINFORM, Issue 51 2005Stefan G. Ebbinghaus Abstract For Abstract see ChemInform Abstract in Full Text. [source] Modeling the Structure of Amorphous MoS3: A Neutron Diffraction and Reverse Monte Carlo Study.CHEMINFORM, Issue 15 2004Simon J. Hibble No abstract is available for this article. [source] Neutron Diffraction of Zirconia-Dispersed Alumina with Increasing Stress and TemperatureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Geoffrey A. Carter Neutron and X-ray diffraction were used to investigate changes in the phase composition and lattice parameters with temperature and pressure of a 20-wt% zirconia-dispersed alumina composite. Neutron diffraction was used to determine the variation of tetragonal/monoclinic zirconia phase abundance for the bulk with stress. The bulk tetragonal/monoclinic ratio decreased by 40% for a stress of 550 MPa. A difference in the tetragonal/monoclinic ratio between the near-surface and the bulk of the processed samples is believed to contribute to observed variations in nonuniform strain in the matrix, which has the effect of prestressing the sample. Placing a stress on the sample initially releases this prestressing. [source] Neutron diffraction studies of magnetic and superconducting compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2004W. B. Yelon Abstract Neutron diffraction is an extremely valuable tool for the investigation of magnetic and superconducting materials, because of its ability to directly observe periodic magnetic structures, determine magnetic moment directions and magnitudes, to observe light elements that are otherwise difficult to locate from X-ray diffraction due to the strong scattering of heavy elements, or to distinguish nearby elements in the periodic chart. This talk will focus on recent studies of superconducting and magnetic oxides that may provide insight into the interaction of magnetism and superconductivity, and into important changes in other transport properties (colossal magneto-resistance, ionic conductivity, etc.). These materials appear to show promise for a wide range of applications, and the neutron studies may not only help to understand their properties, but may also provide direction for synthesis of compounds that may overcome the limitations of those already discovered. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic structures and phase transitions in TbRhSi, DyRhSi and HoRhSiPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003. Gondek Abstract Neutron diffraction and magnetometric measurements show that RRhSi (R = Tb, Dy, Ho) are antiferromagnets below the TN = 25 K for TbRhSi, 14.6 K for DyRhSi and 8.5 K for HoRhSi. For TbRhSi and DyRhSi changes in magnetic structure below TN were detected. For HoRhSi only one stable commensurate magnetic structure was observed. The magnetic structure of DyRhSi was determined for the first time. The new high resolution neutron diffraction data permitted to revise the magnetic phase models of the compounds with R = Tb and Ho. [source] Magnetic ordering of Mn and Ru in (La0.52Ba0.48) (Mn0.51Ru0.49)O3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007S. Y. Wu Abstract Neutron diffraction, dc magnetization, and ac magnetic susceptibility measurements have been performed to study the magnetic properties of perovskite (La0.52Ba0.48) (Mn0.51Ru0.49)O3. The compound crystallizes into a cubic Pmm symmetry with a lattice constant of a = 3.9661(4) Å at room temperature. Two anomalies, at around 160 and 60 K, can clearly be seen in the ac susceptibility results, with the peak positions for both anomalies shifting to a higher temperature as a dc magnetic field is applied. Neutron magnetic diffraction measurements show that the anomalies that occur at high and low temperatures are associated, with the ferromagnetic ordering of the Mn and the Ru spins, respectively. The ordering temperatures for the Mn and Ru spins were found to be at TC (Mn) , 195 K and TC (Ru) , 80 K, with a saturated moment of ,,z,Mn, = 2.21(5),B for the Mn spins and ,,z,Ru, = 1.00(5),B for the Ru spins. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Neutron protein crystallography: beyond the folding structure of biological macromoleculesACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2008Nobuo Niimura Neutron diffraction provides an experimental method of directly locating H atoms in proteins, a technique complementary to ultra-high-resolution X-ray diffraction. Three different types of neutron diffractometers for biological macromolecules have been constructed in Japan, France and the USA, and they have been used to determine the crystal structures of proteins up to resolution limits of 1.5,2.5,Å. Results relating to H-atom positions and hydration patterns in proteins have been obtained from these studies. Examples include the geometrical details of hydrogen bonds, the role of H atoms in enzymatic activity, CH3 configuration, H/D exchange in proteins and oligonucleotides, and the dynamical behavior of hydration structures, all of which have been extracted from these structural results and reviewed. Other techniques, such as the growth of large single crystals and a database of hydrogen and hydration in proteins, are described. [source] Unambiguous determination of H-atom positions: comparing results from neutron and high-resolution X-ray crystallographyACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010Anna S. Gardberg The locations of H atoms in biological structures can be difficult to determine using X-ray diffraction methods. Neutron diffraction offers a relatively greater scattering magnitude from H and D atoms. Here, 1.65,Å resolution neutron diffraction studies of fully perdeuterated and selectively CH3 -protonated perdeuterated crystals of Pyrococcus furiosus rubredoxin (D-rubredoxin and HD-rubredoxin, respectively) at room temperature (RT) are described, as well as 1.1,Å resolution X-ray diffraction studies of the same protein at both RT and 100,K. The two techniques are quantitatively compared in terms of their power to directly provide atomic positions for D atoms and analyze the role played by atomic thermal motion by computing the , level at the D-atom coordinate in simulated-annealing composite D-OMIT maps. It is shown that 1.65,Å resolution RT neutron data for perdeuterated rubredoxin are ,8 times more likely overall to provide high-confidence positions for D atoms than 1.1,Å resolution X-ray data at 100,K or RT. At or above the 1.0, level, the joint X-ray/neutron (XN) structures define 342/378 (90%) and 291/365 (80%) of the D-atom positions for D-rubredoxin and HD-rubredoxin, respectively. The X-ray-only 1.1,Å resolution 100,K structures determine only 19/388 (5%) and 8/388 (2%) of the D-atom positions above the 1.0, level for D-rubredoxin and HD-rubredoxin, respectively. Furthermore, the improved model obtained from joint XN refinement yielded improved electron-density maps, permitting the location of more D atoms than electron-density maps from models refined against X-ray data only. [source] Structural Analysis for Crystalline and Amorphous LnFe2Dx (Ln: Ho, Tb) by X-Ray/Neutron Diffraction and Reverse Monte Carlo Modeling.CHEMINFORM, Issue 41 2004Keiji Itoh Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structural Study of Novel Graphite,Lithium,Calcium Intercalation CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Sébastien Pruvost Abstract Three new layered compounds were synthesised by immersing a pyrographite platelet in a molten Ca,Li alloy creating a new graphite intercalation compound family. The samples were studied by X-ray and neutron diffraction, revealing that the intercalated sheets are polylayered. The study of the 00l reflections allowed us to establish the c -axis stacking of these three phases. The ,-phase exhibits a five-layered intercalated sheet which has something in common with a Li,Ca,Li,Ca,Li slice cut in the CaLi2 structure (ThMn2 Laves phase type). The ,-phase, which is richer in metallic elements and with a greater repeat distance, possesses seven-layered intercalated sheets due to the splitting of the middle lithium plane in three. The third phase is a pseudo-binary compound, containing monolayered sheets and with a formula close to CaC6. Electron microdiffraction allowed us to determine the 2D unit cell for each compound, all of which were commensurate with that of graphite. Charge transfer from the intercalate to the host lattice was evaluated for the three phases from hk0 data, leading to high values. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] 3D Architecture and Load Partition in Eutectic Al-Si Alloys,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Guillermo Requena Abstract The changes of the three dimensional architecture of a eutectic AlSi12 alloy during heat treatment are revealed by means of synchrotron holotomography. The non-destructive nature of the holotomography technique allows to analyze the same volumes in different thermal conditions. The results show a disintegration of the interconnected eutectic Si-lamellae into isolated elongated particles. The load carrying capacity of both types of Si morphologies is studied by in situ neutron diffraction during compression tests. The experimental results are compared to those obtained using a micromechanical model developed for metal matrix composites based on a homogenization approach. The correlation between experiments and calculations shows that the interconnectivity of Si must be considered to account for the strength exhibited by the eutectic alloy. The present study bridges the gap between the already available two-dimensional studies of architecture and properties of the binary AlSi12 alloy and new three-dimensional studies of more complex systems based on this alloy. [source] Stress-Dependent Elastic Properties of Porous Microcracked Ceramics,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Irina Pozdnyakova Abstract Although ceramics are considered linear elastic materials, we have observed a non-linear pseudo-elastic behavior in porous cellular microcracked ceramics such as , -eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non-microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non-microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress-strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non-microcracked SiC. Implications of these findings are discussed. [source] Neutron Diffraction Measurement of Residual Stresses in Friction Stir Processed Nanocomposite Surface Layer,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Hanbing Xu FSP is used to introduce Al2O3 nano-sized particles to an Al 6061 alloy surface to form a hard, strong, and wear-resistant Al-Al2O3 nanocomposite layer. The residual stresses in the FSP zones (with and without Al2O3 particles) have been quantitatively analyzed using neutron diffraction. Results indicated tensile macro-level residual stresses in all three directions with peak values around 100 MPa longitudinally. [source] Teaching crystallography to undergraduate physical chemistry studentsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5-2 2010Virginia B. Pett Teaching goals, laboratory experiments and homework assignments are described for teaching crystallography as part of two undergraduate physical chemistry courses. A two-week teaching module is suggested for introductory physical chemistry, including six to eight classroom sessions, several laboratory experiences and a 3,h computer-based session, to acquaint undergraduate physical chemistry students with crystals, diffraction patterns, the mathematics of structure determination by X-ray diffraction, data collection, structure solution and the chemical insights available from crystal structure information. Student projects and laboratory work for three to four weeks of an advanced physical chemistry course are presented. Topics such as symmetry operators, space groups, systematic extinctions, methods of solving the phase problem, the Patterson map, anomalous scattering, synchrotron radiation, crystallographic refinement, hydrogen bonding and neutron diffraction all lead to the goal of understanding and evaluating a crystallographic journal article. Many of the ideas presented here could also be adapted for inorganic chemistry courses. [source] Characterization of image plates for neutron diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2009Clive Wilkinson A method to measure the overall gain and point-spread function of an image-plate detector system (converter, phosphor, readout electronics) online from single-crystal diffraction patterns is derived. Only with a knowledge of these quantities can one estimate without bias the true standard deviations of the observed integrated intensities of Bragg reflections measured with such a detector. The gain corrected for the point-spread function should ideally be approximately 1.0 to avoid loss of data or precision due to the upper and lower limits of digitization of the diffraction patterns. The gain and the point-spread function are derived for several configurations of the three neutron Laue image-plate diffractometers, LADI, VIVALDI and LADI-III, at the Institut Laue,Langevin. The detective quantum efficiencies (DQE) of these instruments have been measured to be 0.16,(1), 0.57,(2) and 0.46,(3), respectively. It has also been found that the DQE is effectively constant for different times of exposure, despite the fading of the photostimulated luminescent signal during that time. While the results described in this paper concern neutron detection by image plates, the method is equally valid for other integrating detectors and radiations, e.g. CCD detectors and X-rays. [source] Examination of whewellite kidney stones by scanning electron microscopy and powder neutron diffraction techniquesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2009Michel Daudon Kidney stones made of whewellite, i.e. calcium oxalate monohydrate, exhibit various morphological aspects. The crystalline structure of whewellite at the atomic scale was revisited through a single-crystal neutron study at room temperature using a four-circle automated diffractometer. The possible relationships between the various morphological types of whewellite stones and their structural characteristics were examined at the mesoscopic scale by the use of scanning electron microscopy and at the nanometric scale by powder neutron diffraction. All types of whewellite stones displayed a similar structure at the nanometric scale. However, significant differences were found at the mesoscopic scale. In particular, the crystallites in kidney stones resulting from a genetic hyperoxaluria exhibited a peculiar structure. There was a close relationship between stone morphology and crystallite organization at the mesoscopic level and the effectiveness of extracorporeal shockwave lithotripsy. [source] Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] MODY: a program for calculation of symmetry-adapted functions for ordered structures in crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004awa Sikora This paper describes a computer program, based on the theory of groups and representations, which calculates symmetry-adapted functions used for the description of various ordered structures in crystals. It is assumed that the ordered structure, which is formed by a configuration of occupational probabilities, ion displacements, magnetic moments, quadrupolar moments or other local physical quantities, is obtained from a high-symmetry crystal structure with a given space group G, as a result of a symmetry-lowering phase transition. The detailed characteristics of the phase transition are given by the specification of the irreducible representations of group G, active in the transition. The symmetry-adapted functions obtained from the calculation are perfect tools for the construction of model structures, which can be used for comparison with experimental (e.g. neutron diffraction) data, and can be a great help in numerical data elaboration by reducing the number of adjustable parameters describing the structure of a given symmetry. [source] Cold pressing of copper single crystals for a large-area doubly focusing monochromatorJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2004D. F. R. Mildner The design for a large-area doubly focusing neutron monochromator consists of a large number of small square copper single crystals mounted onto thin aluminium blades that both buckle and rotate independently. This avoids the need for large individual alignment mechanisms for each crystal that introduce unacceptably high levels of background. However, it does require that the crystals be oriented such that the diffracting crystallographic planes are parallel to the crystal face. Cold pressing broadens the natural narrow mosaic of the virgin crystal discs to increase the diffracted intensity. This introduces anisotropy into the crystal that determines its orientation in the final monochromator. The alignment procedure used for each crystal before cutting out the square tile in the correct orientation is described. A few crystals are characterized in detail by neutron diffraction at various stages of the operation, revealing the variation in the mosaic width and the angular position of the reciprocal-lattice vector as a function of the azimuthal angle by rotating the crystal about the normal to its face. The twofold symmetry of the mosaic width of the pressed crystal is modulated by the 2, periodicity introduced by the precession of the reciprocal-lattice vector around the crystal face normal. Satisfactorily aligned crystals have a variation in the angular position for diffraction within the allowed tolerance. [source] Mapping of unstressed lattice parameters using pulsed neutron transmission diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2002Javier Roberto Santisteban Stress measurement by neutron diffraction depends critically on knowledge of the unstressed lattice parameter (a0) of the specimen under study. As a result, measurement of stress profiles in components where a0 is not homogeneous throughout the sample, such as welds or carburized surfaces, can be particularly difficult. An efficient solution to this problem is proposed based on the pulsed neutron transmission diffraction technique. This technique exploits the sharp steps in intensity, the so-called Bragg edges, appearing in the transmitted neutron spectra of polycrystalline materials, such steps being produced by coherent scattering from lattice planes. The position of these Bragg edges as defined by the time-of-flight technique is used to determine precisely local interplanar distances. In this work it is shown that the unstressed lattice parameter of thin specimens subjected to plane stress fields can be defined by recording transmission spectra at different sample inclinations, in complete analogy with the sin2, technique used in X-ray diffraction. Moreover, by using an array of detectors it is possible to produce a radiographic `image' of a0 for plane specimens or thin sections out of three-dimensional ones. The capability of the technique is exemplified by mapping the changes in a0 for a ferritic weld that was used as a round robin sample in an international program for standardization of stress measurements by neutron diffraction. [source] Measurement of single-crystal elastic constants by neutron diffraction from polycrystals.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2000Addendum, erratum Correction is made to an equation in a paper by Howard & Kisi [J. Appl. Cryst. (1999), 32, 624633] and additional references are cited. [source] Diffraction-line shift caused by residual stress in polycrystal for all Laue groups in classical approximationsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2000N. C. Popa Analytical formulae for all Laue groups are derived, giving the dependence of the residual elastic strain measured by X-ray and neutron diffraction on the direction in the sample and on the Miller indices. These formulae are valid for isotropic polycrystals in the limits of the Reuss and Voigt approximations and are appropriate for Rietveld refinement. [source] Domain Switching Under Cyclic Mechanical Loading in Lead Zirconate TitanateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006Soodkhet Pojprapai (Imlao) The domain-switching behavior of lead zirconate titanate (PZT) during mechanical cyclic loading between 10 and 150 MPa was investigated by in situ time-of-flight neutron diffraction. The domain-switching behavior was represented by a change of the pole density distribution during cycling. With increasing number of cycles, domain switching becomes saturated, correlating with a decrease in the rate of remnant strain accumulation in the stress,strain curve. Moreover, a relationship was demonstrated between the macroscopic strain and that developed from ferroelastic domain switching. The contribution of ferroelastic strain to the macroscopic strain was calculated from an orientation average of the domain switching distributions and the c/a ratio. The results show that nearly 80% of macroscopic strain arises from ferroelastic domain switching during mechanical cyclic loading. [source] Neutron Thermodiffractometry Study of Calcium Zirconate/Magnesium Oxide Formation in the ZrO2,CaO,MgO SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Sara Serena The reaction process to obtain CaZrO3/MgO specimens in the ZrO2,CaO,MgO system from two mixtures of natural and synthetic raw materials were analyzed by neutron thermodiffractometry; differential thermal analysis,thermogravimetry (DTA-TG) also was used. The results from the different techniques provided a complete description of the decomposition and reaction process in the samples and proved that high-temperature neutron diffraction is a powerful tool for analyzing in situ reactions up to 1250°C in both mixtures. In the present work, the evolution of the crystalline phases, the mechanism and temperature of formation of CaZrO3, and the activation energy were properly established in terms of the neutron thermodiffraction study. [source] Ternary magnetic semiconductors: recent developments in physics and technologyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009V. Tsurkan Abstract Recent results in physics and technology of ternary magnetic oxide and chalcogenide spinels AB2X4 (A = Fe, Mn, Co, Cd, Zn, Hg; B = Cr, Co, Sc, Al; X = O, S, Se) are reviewed. Using magnetic susceptibility, specific heat, thermal expansion, electron-spin resonance, neutron diffraction, broad-band dielectric spectroscopy, and infrared optical spectroscopy, the spin, charge, orbital, and lattice correlations in these compounds were investigated. The novel magnetic ground states, e.g., spin liquid, spin,orbital liquid, and orbital glass, and in triguing effects, like colossal magnetocapacitive coupling, negative thermal expansion, and spin-driven Jahn,Teller structural transformations were revealed. In considering the origin of these phenomena, the concept of geometrical and bond frustration is explored. It relates the interplay of charge, spin, and orbital degrees of freedom with the inherent topological frustration and competing exchange interactions between the magnetic ions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic properties of NdMn2,xFexGe2 (x = 0.3, 0.4 and 1.0) compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003. Gondek Abstract Magnetic properties of the NdMn2,xFexGe2 (x = 0.3, 0.4 and 1.0) are investigated by AC magnetic measurements and neutron diffraction. In ambient pressure in compound with x = 0.3 below 200 K the noncollinear magnetic structure is observed. Above this temperature the magnetic moments transform to the collinear one. For x = 0.4 at 1.5 K the Nd magnetic moments form collinear ferromagnetic structure, while Mn moments noncollinear. With increase of the temperature at T = 50 K Nd moment disappears while Mn moments form two different magnetic structures antiferro- (AF) and ferromagnetic (F). The change between AF and F phases is connected with the change of the lattice constants. For x = 1.0 the Mn moments form collinear antiferromagnetic structure stable in the temperature range between 1.5 K and TN = 203 K. For x = 0.3 the external pressure up to 1.5 GPa causes the change of the critical temperature only, while for x = 0.4 induces the change of the magnetic properties from ferro- to antiferromagnetic. For x = 1.0 the Néel temperature increases with increasing external pressure. The above results indicate that in the NdMn2,xFexGe2 system, the increase in the iron content is followed by a change in chemical bond that influences the magnetic properties. [source] | ||||||||||||||||