2D to 3D Magnetism in Synthetic Micas.

Fe-based mica minerals usually display two opposing magnetic ground states, either they behave as spin-glasses or as layered ferrimagnets. No definite reason has been proposed as an explanation for this duality. This conundrum is unraveled by comparing the synthetic micas KFe[MGe]OX with M═Fe and Ga, X═OH and F.

Antipolar 2D Metallicity with Tunable Valence W (5 ≤ ≤ 5.6) in the Layered Monophosphate Tungsten Bronzes [Ba(PO)]WO.

The newly discovered series of layered monophosphate tungsten bronzes (L-MPTB) [Ba(PO)]WO consist of -layer-thick slabs of WO6 octahedra separated by barium-phosphate spacers. They display a 2D metallic behavior confined in the central part of the perovskite slabs. Here, we report the missing = 2 member of this series, containing the rather uncommon W5+ oxidation state.

Ferromagnetic Mn Sawtooth Chains in A(MnO)(SeO) (A = K, Rb) Quaternary Selenites.

Two quaternary manganese selenites, A(MnO)(SeO) (A = K, Rb), have been synthesized by hydrothermal reactions. They both crystallize in a complex triclinic (P-1) structure built of Jahn-Teller (JT) distorted MnO octahedra, connected into nearly isosceles [MnO] triangles, themselves arranged into so-called "sawtooth (ST) chains". The K and Rb compounds show subtle variations in the orientations of the MnO planes inside the elementary triangles.

CoVO High-Pressure Polymorphs: To Order or Not to Order?

Materials properties are determined by their compositions and structures. In ABO oxides different cation orderings lead to mainly perovskite- or corundum like derivatives with exciting physical properties. Sometimes, a material can be stabilized in more than one structural modification, providing a unique opportunity to explore structure-properties relationship.

Ferrimagnetic and spin glass behaviour in SrMnTiMO (M = Ti and Fe) synthetic crichtonites.

Novel SrMnTiMO (M = Ti and Fe) compounds with a crichtonite-type structure are reported herein. M = Ti shows a ferrimagnetic behavior at = 15 K, while M = Fe creates a ferromagnetic cluster-glass at = 8 K positional disorder. This family offers a promising magnetic playground.

Multivalued Memory via Freezing of Super-Hard Magnetic Domains in a Quasi 2D-Magnet.

The design of high-density non-volatile memories is a long-standing dream, limited by conventional storage "0" or "1" bits. An alternative paradigm exists in which regions within candidate materials can be magnetized to intermediate values between the saturation limits. In principle, this paves the way to multivalued bits, vastly increasing storage density.

Layered Monophosphate Tungsten Bronzes [Ba(PO ) ]W O : 2D Metals with Locked Charge-Density-Wave Instabilities.

Phosphate tungsten and molybenum bronzes represent an outstanding class of materials displaying textbook examples of charge-density-wave (CDW) physics among other fundamental properties. Here we report on the existence of a novel structural branch with the general formula [Ba(PO ) ][W O ] (m=3, 4 and 5) denominated 'layered monophosphate tungsten bronzes' (L-MPTB). It results from thick [Ba(PO ) ] spacer layers disrupting the cationic metal-oxide 2D units and enforcing an overall trigonal structure.

The Chemistry, Recrystallization and Thermal Expansion of Brannerite from Akchatau, Kazakhstan.

Numerous studies expose the potential of brannerite to become a good matrix, concentrating fission products and actinides. Minerals can complement the data collected from the synthetic materials and offer an advantage of a long-time exposure to radiation. Natural metamict brannerite from Akchatau, Kazakhstan, and its annealed sample were studied by EPMA, Raman spectroscopy, TGA, DSC, XRD and HTXRD.

Crystalline Molecular Assemblies of Complexes Showing Eightfold Coordinated Niobium(IV) Dodecahedral Geometry in the Pyridine-Dicarboxylic Acid System.

The reactivity of 2,3-pyridine-dicarboxylic (known as quinolinic or qui) acid and 2,5-pyridine-dicarboxylic (known as isocinchomeronic or icc) acid has been investigated as a complexing agent toward the niobium(IV) tetrachloride precursor (NbCl·2THF) in different organic solvent mixtures. It resulted in the isolation of four crystalline assemblies of mononuclear coordination complexes [Nb(L)·solvent], where L is the monoprotonated quinolinate (Hqui) ligand (complexes -) or the monoprotonated isocinchomeronate ligand (complex ). For each complex, the discrete niobium(IV) center is eightfold coordinated to four oxygen atoms from the deprotonated carboxylate arm and four nitrogen atoms from the pyridine part of the dicarboxyl ligand with a dodecahedral environment [NbON].

1 : 1 Ca :Cu A-site Order in a Ferrimagnetic Double Double Perovskite.

Cation ordering in ABX perovskites is important to structural, physical and chemical properties. Here we report discovery of CaCuFeReO with the tetragonal AA'BB'O double double perovskite structure that was previously only reported for A'=Mn compositions. CaCuFeReO occurs in the same phase field as CaCu Fe Re O demonstrating that different A-cation ordered peroskites may be obtained in the same chemical system.

Preparation, characterization and DFT+U study of the polar Fe-based phase BaFeZnInS containing = 5/2 zigzag chains.

The polar magnetic chalcogenide phase BaFeZnInS was synthesized and its structure was solved by single crystal XRD. It is the first member with a 3d magnetic metal (Fe) in the PbZnGaS-type structure family of wide bandgap materials with non-linear optical properties. The three-dimensional framework possesses a low dimensional magnetic character through the presence of weakly interacting zig-zag chains made of corner-sharing FeS tetrahedra forming chain 1, [FeS].

Compressibility of structural modulation waves in the chain compounds BaCoXO (X = As, P): a powder study.

BaCoXO (X = As, P) are built on magnetic 1D units in which strong aperiodic undulations originate from incommensurate structural modulations with large atomic displacive amplitudes perpendicular to the chain directions, resulting in very unique multiferroic properties. High-pressure structural and vibrational properties of both compounds have been investigated by synchrotron X-ray powder diffraction and Raman spectroscopy at room temperature and combined with density functional calculations. A structural phase transition is observed at 1.

Hybrid electrons in the trimerized GaVO.

Mixed-valent transition-metal compounds display complex structural, electronic and magnetic properties, which often intricately coexist. Here, we report the new ternary oxide GaVO, a structural sibling of skyrmion-hosting lacunar spinels. GaVO contains a vanadium trimer and an original spin-orbital-charge texture that forms upon the structural phase transition at T = 68 K followed by the magnetic transition at T = 35 K.

From ( = 1) Spin Hexamer to Spin Tetradecamer by CuO Interstitials in ACuO(CuO)(SO) (A = alkali).

(Na,K)CuO(SO) compounds form structural chains of Cu hexameric units with nominal = 1 spins due to the interplay between inner strong antiferromagnetic and ferromagnetic exchanges. We show here that the lattice relaxation after the replacement of alkali by larger Rb and Cs ones is accompanied by the insertion of neutral CuO species into (Rb,Cs)CuO(CuO)(SO) phases. Structurally, interstitial CuO links the next two Cu units in longer Cu tetradecameric ones.

A high dimensional oxysulfide built from large iron-based clusters with partial charge-ordering.

Herein we report the original BaFeZnSSiO oxysulfide which crystallizes in a new structural type. Contrary to the usual oxychalcogenides, it crystallizes with a non-centrosymmetric 3D spatial network structure built from large magnetic clusters consisting of twelve (Fe/Zn)SO tetrahedra decorating a central FeS octahedron and exhibiting a spin glass state.

MnMnNbO: high-pressure triple perovskite with 1 : 2 B-site order and modulated spins.

The first triple perovskite with Mn in A- and 1 : 2 B-site order MnMnNbO, prepared using high pressure phase transformation of the magnetodielectric MnNbO, is reported herein. It has a complex magnetic behaviour with a transition from a collinear AFM into an evolving incommensurate spin density wave (SDW) further stabilised into a lock-in structure dictated by the B-site order.

Cycloidal Magnetic Order Promoted by Labile Mixed Anionic Paths in M(SeO)F (M = Mn, Ni).

Two M(SeO)F fluoro-selenites (M = Mn, Ni) have been synthesized using optimized hydrothermal reactions. Their 3D framework consists of 1D-[MOF]chains of edge-sharing octahedra with a rare topology of alternating O-O and F-F μ bridges. The interchain corner-sharing connections are assisted by the mixed O vs F anionic nature and develop a complex set of M-X-M superexchanges as calculated by LDA+.

= 1/2 Chain in BiVOF: Spin Dimers versus Photoanodic Properties.

BiVOF was prepared, characterized, and identified as a unique example of bismuth vanadyl oxyhalide with paramagnetic V centers. Its crystal structure shows 1D magnetic units with rare alternation of edge-sharing O-O and F-F μ bridges along the octahedral chains. Structural pairing across the O edges induces antiferromagnetic spin dimers ( = 0) with / ≈ 300 K, ∼15 times greater than the exchange across the F bridges, within a non-ordered magnetic ground state.

Complex magnetism in NiTeO-type CoTeO and high-pressure polymorphs of MnCoTeO solid solutions.

New NiTeO-type (NTO) and double perovskite (DPv) polymorphs of CoTeO are synthesised at pressures of 15 GPa. A complex elliptic helical magnetic order is observed in the NTO polymorph (T = 58 K) that reorientates (42 K) and further splits (T = 23.5 K) creating a coexisting helix.

Magnetic Structures of MnTaO and Interpretation as an Hexagonal A-site Manganite.

MnTaO is presented as the first hexagonal A-site manganite. Based on simple rules, the structure is compatible with a 14H-layer () stacking sequence that is related to BaVO and BaCrO high-pressure polymorphs. The A-site overstoichiometry is explained through difference in ionic radii sizes between Ba and Mn.

Oxysulfide Ba(VOS)(S) Combining Disulfide Channels and Mixed-Anion Tetrahedra and Its Third-Harmonic-Generation Properties.

Mixed-anion compounds are among the most promising systems to design functional materials with enhanced properties. In particular, heteroleptic environments around transition metals allow tuning of the polarity or band-gap engineering for instance. We present the original oxysulfide Ba(VOS)(S), the fifth member in the quaternary system Ba-V-S-O.

Sequential Spin State Transition and Intermetallic Charge Transfer in PbCoO.

Spin state transitions and intermetallic charge transfers can essentially change material structural and physical properties while excluding external chemical doping. However, these two effects have rarely been found to occur sequentially in a specific material. In this article, we show the realization of these two phenomena in a perovskite oxide PbCoO with a simple ABO composition under high pressure.

Magnetic frustration in the high-pressure MnMnTeO (MnTeO-II) double perovskite.

A new double perovskite Mn2MnTeO6 has been obtained by high pressure phase transformation of a corundum-related precursor. It is antiferromagnetic below 36 K and develops a magnetic structure with magnetic moments of 4.8 μB and 3.

Metamagnetic Transitions versus Magnetocrystalline Anisotropy in Two Cobalt Arsenates with 1D Co Chains.

We have investigated two original hydrated cobalt arsenates based on Co octahedral edge-sharing chains. Their different magnetocrystalline anisotropies induce different types of metamagnetic transitions: spin-flop versus spin-flip. In both compounds, a strong local anisotropy (Ising spins) is favored by the spin-orbit coupling present in the CoO octahedra, while ferromagnetic (FM) exchanges predominate in the chains.