Introducing a unified magnetic space-group symbol.

The two commonly used systems of magnetic space-group (MSG) symbols, with accompanying numbers and settings, are those of Belov-Neronova-Smirnova (BNS) and Opechowski-Guccione (OG). The symbols from both systems have been used for several decades now. Both have advantages and disadvantages.

Influence of Polymorphism on the Magnetic Properties of CoTeO Spinel.

This study presents the influence of polymorphism on the magnetic properties of CoTeO. This compound with a spinel-like structure [Co][CoTe]O was synthesized into two polymorphs: one disordered within a cubic 3̅ structure, where Co and Te ions are randomly distributed on the octahedral B sites [the disordered polymorph can also be presented as an inverse spinel of the formula Co(CoTe)O] and the other ordered with a cubic 432 structure where Co and Te ions are ordered on the B sites. The macroscopic magnetic measurements showed that both polymorphs present a ferrimagnetic ordering, below ∼40 K, and a second transition is also observed at 27 K for the ordered polymorph.

Crystal engineering and ferroelectricity at the nanoscale in epitaxial 1D manganese oxide on silicon.

Ferroelectric oxides have attracted much attention due to their wide range of applications, particularly in electronic devices such as nonvolatile memories and tunnel junctions. As a result, the monolithic integration of these materials into silicon technology and their nanostructuration to develop alternative cost-effective processes are among the central points in the current technology. In this work, we used a chemical route to obtain nanowire thin films of a novel Sr1+δMn8O16 (SMO) hollandite-type manganese oxide on silicon.

Experimental Evidence of the Coexistence of Proper Magnetic and Structural Incommensurability on the [CHNH][Ni(COOH)] Compound.

The present work is dedicated to characterization of the structural phase transition and incommensurate magnetic structure of the [CHNH][Ni(COOH)] () perovskite-like metal-organic compound. The structural and magnetic characterization has been performed through variable-temperature single-crystal and powder neutron diffraction. Compound crystallizes in the orthorhombic space group at room temperature.

Spin-density studies of the multiferroic metal-organic compound [NH(CH)][FeFe(HCOO)].

Polarized neutron diffraction is used to study in depth the magnetic properties of the heterometallic compound [NH(CH)][FeFe(HCOO)] and give insight into its magnetic behaviour, addressing open questions that will contribute to a better understanding of this attention-grabbing material and other related ones. Previous results revealed that upon cooling, the magnetic moments of the Fe and Fe sites do not order simultaneously: the magnetization of the Fe site increases faster than that of the Fe sites. Unpolarized neutron diffraction measurements at 2 K with no external field revealed some discrepancies in the saturation value of the magnetic signal on the Fe sites and in the ferromagnetic moment along the axis.

Incommensurate structures of the [CHNH][Co(COOH)] compound.

The present article is devoted to the characterization of the structural phase transitions of the [CHNH][Co(COOH)] () perovskite-like metal-organic compound through variable-temperature single-crystal neutron diffraction. At room temperature, compound crystallizes in the orthorhombic space group (phase ). A decrease in temperature gives rise to a first phase transition from the space group to an incommensurate phase (phase ) at approximately 128 K.

Switching of the Chiral Magnetic Domains in the Hybrid Molecular/Inorganic Multiferroic (ND)[FeCl(DO)].

(ND)[FeCl(DO)] represents a promising example of the hybrid molecular/inorganic approach to create materials with strong magneto-electric coupling. Neutron spherical polarimetry, which is directly sensitive to the absolute magnetic configuration and domain population, has been used in this work to unambiguously prove the multiferroicity of this material. We demonstrate that the application of an electric field upon cooling results in the stabilization of a single-cycloidal magnetic domain below 6.

Microscopic Insights on the Multiferroic Perovskite-Like [CH NH ][Co(COOH) ] Compound.

The characterization of the crystal structure, phase transitions, magnetic structure and dielectric properties has been carried out on [CH NH ][Co(COOH) ] (1) perovskite-like metal-organic compound through variable-temperature single-crystal and powder neutron and X-ray diffraction and relative permittivity measurements. The paraelectric to antiferroelectric-like phase transition observed at around 90 K is triggered by a structural phase transition; the structural studies show a change from Pnma space group at RT (1A) to P2 /n space group at low temperature (1B). This phase transition involves the occurrence of small distortions in the framework and counterions.

Magnetic Structures of Heterometallic M(II)-M(III) Formate Compounds.

A study of the magnetic structure of the [NH(CH)][FeM(HCOO)] niccolite-like compounds, with M = Co (2) and Mn (3) ions, has been carried out using neutron diffraction and compared with the previously reported Fe-containing compound (1). The inclusion of two different metallic atoms into the niccolite-like structure framework leads to the formation of isostructural compounds with very different magnetic behaviors due to the compensation or not of the different spins involved in each lattice. Below T, the magnetic order in these compounds varies from ferrimagnetic behavior for 1 and 2 to an antiferromagnetic behavior with a weak spin canting for 3.

Magnetic Structures of Orthorhombic LiM(SO) (M = Co, Fe) and LiFe(SO) (x = 1, 1.5) Phases.

We report herein on the magnetic properties and structures of orthorhombic LiM(SO) (M = Co, Fe) and their oxidized phases LiFe(SO) (x = 1, 1.5), which were previously studied as potential cathode materials for Li-ion batteries. The particular structure of these orthorhombic compounds (space group Pbca) consists of a three-dimensional network of isolated MO octahedra enabling solely super-super-exchange interactions between transition metals.

Structural and magnetic properties of the low-dimensional fluoride β-FeF3(H2O)2·H2O.

We have reinvestigated the crystal structure of the low-dimensional fluoride β-FeF3(H2O)2·H2O using high resolution neutron and X-ray diffraction data. Moreover we have studied the magnetic behavior of this material combining medium resolution and high flux neutron powder diffraction together with magnetic susceptibility measurements. This fluoride compound exhibits vertex-shared 1D Fe(3+) octahedral chains, which are extended along the c-axis.

Chiral habit selection on nanostructured epitaxial quartz films.

Understanding the crystallization of enantiomorphically pure systems can be relevant to diverse fields such as the study of the origins of life or the purification of racemates. Here we report on polycrystalline epitaxial thin films of quartz on Si substrates displaying two distinct types of chiral habits that never coexist in the same film. We combine Atomic Force Microscopy (AFM) analysis and computer-assisted crystallographic calculations to make a detailed study of these habits of quartz.

Crystallization of hollow mesoporous silica nanoparticles.

Complex 3D macrostructured nanoparticles are transformed from amorphous silica into pure polycrystalline α-quartz using catalytic quantities of alkaline earth metals as devitrifying agent. Walls as thin as 10 nm could be crystallized without losing the architecture of the particles. The roles of cation size and the mol% of the incorporated devitrifying agent in crystallization behavior are studied, with Mg(2+), Ca(2+), Sr(2+) and Ba(2+) all producing pure α-quartz under certain conditions.

Synthesis, crystal structure, and magnetic characterization of the three-dimensional compound [Co2(cbut)(H2O)3]n (H4cbut = 1,2,3,4-cyclobutanetetracarboxylic acid).

A novel cobalt(II) complex of formula [Co2(cbut)(H2O)3]n (1) (H4cbut = 1,2,3,4-cyclobutanetetracarboxylic acid) has been synthesized under hydrothermal conditions and its crystal structure has been determined by means of synchrotron radiation and neutron powder diffraction. The crystal structure of 1 consists of layers of cobalt(II) ions extending in the bc-plane which are pillared along the crystallographic a-axis through the skeleton of the cbut(4-) ligand. Three crystallographically independent cobalt(II) ions [Co(1), Co(2), and Co(3)] occur in 1.

Neutron diffraction studies of the molecular compound [Co2(bta)]n (H4bta =1,2,4,5-benzenetetracarboxylic acid): in the quest of canted ferromagnetism.

The exchange mechanism and magnetic structure of the organic-inorganic layered molecule-based magnet [Co2(bta)]n (1) (H4bta =1,2,4,5-benzenetetracarboxylic acid) have been investigated through variable-temperature magnetic susceptibility measurements and supported with a series of neutron diffraction experiments. Cryomagnetic studies have shown an antiferromagnetic ordering at a transition temperature of 16 K that is followed by the appearance of a weak ferromagnetism below 11 K. The weak antiferromagnetic interlayer interaction plays an important role in this system in spite of the long interlayer separation.

Marinite Li2M(SO4)2 (M = Co, Fe, Mn) and Li1Fe(SO4)2: model compounds for super-super-exchange magnetic interactions.

New materials initially designed for battery electrodes are often of interest for magnetic study, because their chemical compositions include 3d transition metals. We report here on the magnetic properties of marinite phases Li2M(SO4)2 (M = Fe, Co, Mn) and Li1Fe(SO4)2, which all order antiferromagnetically at low temperature. From neutron powder diffraction, we propose a model for their ground-state magnetic structures.

The role of order-disorder transitions in the quest for molecular multiferroics: structural and magnetic neutron studies of a mixed valence iron(II)-iron(III) formate framework.

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH(2)(CH(3))(2)](n)[Fe(III)Fe(II)(HCOO)(6)](n). The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19.

Structural investigation of the negative thermal expansion in yttrium and rare earth molybdates.

The Sc(2)(WO(4))(3)-type phase (Pbcn) of Y(2)(MoO(4))(3), Er(2)(MoO(4))(3) and Lu(2)(MoO(4))(3) has been prepared by the conventional solid-state synthesis with preheated oxides and the negative thermal expansion (NTE) has been investigated along with an exhaustive structural study, after water loss. Their crystal structures have been refined using the neutron and x-ray powder diffraction data of dehydrated samples from 150 to 400 K. The multi-pattern Rietveld method, using atomic displacements with respect to a known structure as parameters to refine, has been applied to facilitate the interpretation of the NTE behavior.

Low temperature neutron diffraction studies in [Mn3(suc)2(ina)2]n: an homometallic molecular 3D ferrimagnet.

Neutron diffraction techniques have been used to determine the low temperature crystal structure and to shed light on the magnetic behavior of the [Mn(3)(suc)(2)(ina)(2)](n) (suc = succinate and ina = isonicotinate) complex. The ferromagnetic signal observed below T(c) ≈ 5 K in this compound is due to a noncompensation of homometallic spins in the 3D framework. The Mn(II) magnetic moments obtained from neutron diffraction refinements are slightly lower than those observed for isolated Mn(II) ions; this can be due to covalent spin delocalization or geometrical magnetic fluctuations.

Single crystalline La0.7Sr0.3MnO3 molecular sieve nanowires with high temperature ferromagnetism.

Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO(2) and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates.

Insight into ramsdellite LI(2)Ti(3)O(7) and its proton-exchange derivative.

Despite being proven to be a good lithium-ion conductor 30 years ago, the crystal structure of the ramsdellite-like Li(2)Ti(3)O(7) has remained uncertain, with two potential models for locating the lithium ions in the structure. Although the model presently accepted states that both lithium and titanium occupy the octahedral sites in the framework, evidence against this model are provided by (6)Li and (7)Li MAS NMR spectroscopy. Thus, about 14% of these octahedral positions are empty since no lithium in octahedral coordination is present in the material.

Synthesis and characterization of the ultramarine-type analog Na(8-x)[Si6Al6O24] x (S2,S3,CO3)(1-2).

The use of nitrite sodalite as a precursor to prepare new blue ultramarine analogs has been investigated. The encapsulation of the chromophores inside of beta cages was achieved by heating the nitrite sodalite precursor with a mixture of sodium carbonate, sulfur, and a reducing agent at about 1000 K under airtight conditions. The obtained new blue ultramarine-type material was characterized by means of X-ray and neutron powder diffraction, transmission electron microscopy, 29Si magic-angle-spinning NMR, IR, Raman, and diffuse reflectance spectroscopies.

Synchrotron powder diffraction characterization of the zeolite-based (p-N,N-dimethylnitroaniline-mordenite) guest-host phase.

The crystal structure of a new phase consisting of the inclusion of the hyperpolarizable molecule p-N,N-dimethylnitroaniline (dimethyl-para-nitroaniline or dmpNA) in the large-pore zeolite mordenite (MOR) has been determined from high-resolution synchrotron powder diffraction at 300 and 90 K. The unit-cell parameters and space group at 300 K are similar to those of as-synthesized mordenite. The crystallographic study indicates that the MOR straight channels are almost fully loaded with molecules that are disordered over eight symmetry-related sites.

A comparison of the magnetic structures of KMn(4)(PO(4))(3) and KCo(4)(PO(4))(3) based on the connectivity of the coordination polyhedra.

The crystal structures of KMn(4)(PO(4))(3) and KCo(4)(PO(4))(3) have been determined by neutron diffraction at room temperature. Both compounds are orthorhombic with similar cell parameters, but they crystallize in different space groups, Pnam for the Mn phosphate and Pnnm for the Co analogue. On the basis of the metal cation polyhedra and their connectivity, the crystal structures have been rationalised, which allow interpretation of the main magnetic interactions between them.