Single-crystal Neutron Diffraction Research Articles

On the crystal-chemistry of inderite, Mg[B3O3(OH)5](H2O)4·H2O

The crystal chemistry of inderite, a hydrous borate with known ideal formula MgB3O3(OH)5·5H2O from the Kramer deposit, was re-investigated by electron probe micro-analysis in wavelength dispersive mode, laser ablation-(multi collector-)inductively coupled plasma-mass spectrometry and single-crystal neutron diffraction. The chemical data prove that the real composition of the investigated inderite is substantially identical to the ideal one, with insignificant content of potential isomorphic substituents, so that, excluding B, inderite does not contain any other industrially-relevant element (e.g., Li concentration is lower than 2.5 wt ppm, Be or REE lower than 0.1 wt ppm). The average δ11BNIST951 value of ca. − 7 ‰ lies within the range of values in which the source of boron is ascribable to terrestrial reservoirs (e.g., hydrothermal brines), rather than to marine ones. Neutron structure refinements, at both 280 and 10 K, confirm that the building units of the structure of inderite consist of: two BO2(OH)2 tetrahedra (B-ion in sp3 electronic configuration) and one BO2(OH) triangle (B-ion in sp2 electronic configuration), linked by corner-sharing to form a (soroborate) B3O3(OH)5 ring, and a Mg-octahedron Mg(OH)2(OH2)4. The B3O3(OH)5 ring and the Mg-octahedron are connected, by corner-sharing, to form an isolated Mg(H2O)4B3O3(OH)5 (molecular) cluster. The tri-dimensional edifice of inderite is therefore built by heteropolyhedral Mg(H2O)4B3O3(OH)5 clusters mutually connected by H-bonds, mediated by the zeolitic (“interstitial”) H2O molecules lying between the clusters, so that the correct form of the chemical formula of inderite is Mg[B3O3(OH)5](H2O)4·H2O, rather than MgB3O3(OH)5·5H2O. All the thirteen independent oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. This confirms the pervasive nature and the important role played by the H-bonding network on the structural stability of inderite. The differences between the crystal structure of the two dimorphs inderite and kurnakovite are discussed.

Magnetic structure and properties of the honeycomb antiferromagnet [Na(OH2)3]Mn(NCS)3.

We report the magnetic structure and properties of a thiocyanate-based honeycomb magnet [Na(OH2)3]Mn(NCS)3 which crystallises in the unusual low-symmetry trigonal space group P3̄. Magnetic measurements on powder samples show this material is an antiferromagnet (ordering temperature TN,mag = 18.1(6) K) and can be described by nearest neighbour antiferromagnetic interactions J = -11.07(4) K. A method for growing neutron-diffraction sized single crystals (>10 mm3) is demonstrated. Low temperature neutron single crystal diffraction shows that the compound adopts the collinear antiferromagnetic structure with TN,neut = 18.94(7) K, magnetic space group P3̄'. Low temperature second-harmonic generation (SHG) measurements provide no evidence of breaking of the centre of symmetry.

New insight into tuning magnetic phases of RMn6Sn6 kagome metals

Predicting magnetic ordering in kagome compounds offers the possibility of harnessing topological or flat-band physical properties through tuning of the magnetism. Here, we examine the magnetic interactions and phases of ErMn6Sn6 which belongs to a family of RMn6Sn6, R = Sc, Y, Gd–Lu, compounds with magnetic kagome Mn layers, triangular R layers, and signatures of topological properties. Using results from single-crystal neutron diffraction and mean-field analysis, we find that ErMn6Sn6 sits close to the critical boundary separating the spiral-magnetic and ferrimagnetic ordered states typical for non-magnetic versus magnetic R layers, respectively. Finding interlayer magnetic interactions and easy-plane Mn magnetic anisotropy consistent with other members of the family, we predict the existence of a number of temperature and field dependent collinear, noncollinear, and noncoplanar magnetic phases. We show that thermal fluctuations of the Er magnetic moment, which act to weaken the Mn-Er interlayer magnetic interaction and quench the Er magnetic anisotropy, dictate magnetic phase stability. Our results provide a starting point and outline a multitude of possibilities for studying the behavior of Dirac fermions in RMn6Sn6 compounds with control of the Mn spin orientation and real-space spin chirality.

Emergence of the isotropic Kitaev honeycomb lattice α− RuCl3 and its magnetic properties

We present a comprehensive investigation of the crystal and magnetic structures of the van der Waals antiferromagnet α− RuCl3 using single crystal x-ray and neutron diffraction. The crystal structure at room temperature is a monoclinic ( C2/m ). However, with decreasing temperature, a remarkable first-order structural phase transition is observed, leading to the emergence of a rhombohedral ( R3ˉ ) structure characterized by three-fold rotational symmetry forming an isotropic honeycomb lattice. On further cooling, a zigzag-type antiferromagnetic order develops below TN=6∼6.6 K. The critical exponent of the magnetic order parameter was determined to be β=0.11(1) , which is close to the two-dimensional Ising model. Additionally, the angular dependence of the magnetic critical field of the zigzag antiferromagnetic order for the polarized ferromagnetic phase reveals a six-fold rotational symmetry within the ab− plane. These findingsreflect the symmetry associated with the Ising-like bond-dependent Kitaev spin interactions and underscore the universality of the Kitaev interaction-dominated antiferromagnetic system.

Characterization of Water Structure and Phase Behavior within Metal-Organic Nanotubes.

Water behavior under nanoconfinement varies significantly from that in the bulk but also depends on the nature of the pore walls. Hybrid compound offers the ideal system to explore water behavior in complex materials, so a model metal-organic nanotube (UMONT) material was utilized to explore the behavior of water between 100 and 293 K. Single-crystal X-ray and neutron diffraction revealed the formation of a filled Ice-I arrangement that was previously predicted to only occur under high pressures. 17O NMR spectra suggest that the onset of melting for the water in the UMONT channels occurs at 98 K and the presence of ice-like water up to 293 K, indicating that the complete ice-water transition does not occur before dehydration of the material. Overall, the water behavior differs significantly from hydrophobic single-walled carbon nanotubes indicating precise control over water can be achieved through rational design of hybrid materials.

Structure and properties of NdCuGa[formula omitted] single crystals

This manuscript reports on the structural and magnetic properties of NdCuGa3 using powder and single crystal X-ray diffraction (XRD), zero-field single crystal neutron diffraction, magnetization, and specific heat measurements. Our XRD on a single crystal specimen of NdCuGa3 confirmed that it crystallizes in the tetragonal BaNiSi3-type structure. A magnetic phase transition at TN= 3.3 K is assessed using specific heat and ac magnetic susceptibility measurements. No additional anomaly below TN down to 50 mK was detected by performing specific heat measurements. Neutron single crystal diffraction data collected at T= 300 mK confirm the antiferromagnetic phase below TN= 3.3 K with the propagation vector τ→= (0.2, 0, 0). Possible magnetic structure solutions of NdCuGa3 are discussed.

Incommensurate magnetic structure of CrAs at low temperatures and high pressures.

The magnetic structure of chromium arsenide CrAs is studied with neutron powder diffraction at ambient pressure in the temperature range 1.5-300 K as well as with neutron single-crystal diffraction at 2 K and 0.12 GPa. The material undergoes an anti-isostructural phase transition at TN = 267 K and atmospheric conditions, in which both orthorhombic phases have the same space-group symmetry (Pnma, Z = 4) but different distortions of the parent hexagonal structure of the NiAs type (P63/mmc, Z = 2). The magnetic structure below TN is incommensurate with the propagation vector k = (0, 0, kc). At ambient pressure, the component kc decreases from kc = 0.3807 (7) at 260 K to kc = 0.3531 (6) at 50 K. Below this temperature, it is basically constant. With increasing pressure at 2 K, kc is also constant within standard uncertainties [kc = 0.353 (2)]. For the analysis of the magnetic structure, a group-theoretical approach based on the space group of the nuclear structure and its subgroups is used. To avoid falling into false minima in the refinements, a random search for magnetic moments in the models is implemented. In the literature, the magnetic structure has been determined on the basis of powder diffraction data as a double helix propagating along the c axis. Although this double-helical model leads to satisfactory agreement factors for our powder data, it does not reproduce the intensities of the magnetic satellite reflections measured on single-crystal data in a satisfactory way and can therefore be discarded. Instead, several other models are found that lead to better agreement. Each of them is spiral-like with directional components in all three directions and with no spin-density wave character that would cause a non-constant magnetic moment. In all these models, the ordering of the spins is neither a pure helix nor a pure cycloid. Instead, the unit vectors of the spin rotation planes make an angle α, 0° < α < 90°, with respect to the c* direction. The model in superspace group P21.1'(α0γ)0s yields the best agreement factors in the refinements of the neutron single-crystal and powder diffraction data. This model is unique as it is the only one in which all the magnetic moments rotate with the same chirality.

Benchmark Crystal Structure of Defect-Free Spinel ZnFe2O4.

Accurate structural models are of paramount importance for elucidating structure-property relationships in functional materials. Spinels (AB2O4) form a highly important family of materials with complex crystal structures, and subtle structural details have a critical bearing on understanding their physical properties. In some spinels, the space group symmetry is debated, and in general, point defects such as cation inversion and interstitials add complexity. Most studies of spinels concern powder materials, and this challenges deep structural characterization. In fact, most published spinel structures have dubious atomic displacement parameters (ADPs), which is a typical sign of problematic structural description in the refinement of diffraction data. Here, we use various X-ray and neutron diffraction techniques to establish a benchmark crystal structure for the essentially defect-free spinel ferrite ZnFe2O4, which is a widely studied frustrated magnet. It is shown that the appearance of Fd3̅m forbidden reflections in the ZnFe2O4 single-crystal neutron diffraction data is an artifact of multiple scattering rather than the loss of inversion symmetry. We then provide benchmark ADPs and demonstrate how strongly these parameters affect the refined cation inversion. The ADPs reported here may be used as reference data to test the soundness of refined structural models, possibly to constrain those based on suboptimal data quality, and thereby provide a more accurate fundamental understanding of the structure-property relationship in spinel-type materials.

The hydrogen-bond network in sodium chloride tridecahydrate: analogy with ice VI.

The structure of a recently found hyperhydrated form of sodium chloride (NaCl·13H2O and NaCl·13D2O) has been determined by in situ single-crystal neutron diffraction at 1.7 GPa and 298 K. It has large hydrogen-bond networks and some water molecules have distorted bonding features such as bifurcated hydrogen bonds and five-coordinated water molecules. The hydrogen-bond network has similarities to ice VI in terms of network topology and disordered hydrogen bonds. Assuming the equivalence of network components connected by pseudo-symmetries, the overall network structure of this hydrate can be expressed by breaking it down into smaller structural units which correspond to the ice VI network structure. This hydrogen-bond network contains orientational disorder of water molecules in contrast to the known salt hydrates. An example is presented here for further insights into a hydrogen-bond network containing ionic species.

Development of an Iron(II) Complex Exhibiting Thermal- and Photoinduced Double Proton-Transfer-Coupled Spin Transition in a Short Hydrogen Bond.

Multiple proton transfer (PT) controllable by external stimuli plays a crucial role in fundamental chemistry, biological activity, and material science. However, in crystalline systems, controlling multiple PT, which results in a distinct protonation state, remains challenging. In this study, we developed a novel tridentate ligand and iron(II) complex with a short hydrogen bond (HB) that exhibits a PT-coupled spin transition (PCST). Single-crystal X-ray and neutron diffraction measurements revealed that the positions of the two protons in the complex can be controlled by temperature and photoirradiation based on the thermal- and photoinduced PCST. The obtained results suggest that designing molecules that form short HBs is a promising approach for developing multiple PT systems in crystals.

Structure determination of high-pressure phases of hydrogen-bonding crystals by the combination of in situ single-crystal X-ray diffraction and neutron diffraction

Structure determination of high-pressure phases of hydrogen-bonding crystals by the combination of <i>in situ</i> single-crystal X-ray diffraction and neutron diffraction

What contribution does neutron single-crystal diffraction make to chemical crystallography? KOALA, Cobra and LaueG yielded structures published for maximum impact for chemistry and crystallography

What contribution does neutron single-crystal diffraction make to chemical crystallography? KOALA, Cobra and <i>LaueG</i> yielded structures published for maximum impact for chemistry and crystallography

Advances in single-crystal neutron diffraction

Advances in single-crystal neutron diffraction

Machine-learning assisted automation of single-crystal neutron diffraction

Machine-learning assisted automation of single-crystal neutron diffraction

Where the H is the interstitial: single-crystal neutron diffraction studies of complex metal hydrides

Where the H is the interstitial: single-crystal neutron diffraction studies of complex metal hydrides

Magnetic ground state and perturbations of the distorted kagome Ising metal TmAgGe

Magnetic order and excitations of the distorted kagome intermetallic magnet TmAgGe are explored using a variety of methods, including single-crystal neutron diffraction, inelastic neutron scattering, Monte Carlo simulations, and the random phase approximation. The magnetic properties are governed by strong, local single-ion anisotropy and geometrically frustrated magnetic exchanges. The authors establish multi-k structures at several different magnetic field configurations and model effective exchange parameters using field-dependencies of the magnetic neutron diffraction reflections and the weakly dispersive crystal electric field mode.

Field-induced partial disorder in a Shastry-Sutherland lattice

A 2-Q antiferromagnetic order of the ferromagnetic dimers was found below TN = 2.9 K in the Shastry-Sutherland lattice BaNd2ZnS5 by single crystal neutron diffraction. The magnetic order can be understood by the orthogonal arrangement of local Ising Nd spins, identified by polarized neutrons. A field was applied along [1 -1 0] to probe the observed metamagnetic transition in the magnetization measurement. The field decouples two magnetic sublattices corresponding to the propagation vectors q1 = (½, ½, 0) and q2 = (−½, ½, 0), respectively. Each sublattice shows a “stripe” order with a Néel-type arrangement in each single layer. The “stripe” order with q1 remains nearly intact up to 6 T, while the other one with q2 is suppressed at a critical field Hc ~1.7 T, indicating a partial disorder. The Hc varies with temperature and is manifested in the H-T phase diagram constructed by measuring the magnetization in BaNd2ZnS5.

Anomalous Hall effect and magnetic structure of the topological semimetal ( Mn0.78Fe0.22)Ge3

Me$_{3+\delta}$Ge, being a Weyl semimetal, shows a large anomalous Hall effect (AHE), which decreases slowly with an increase in $\delta$ from 0.1 to 0.4. However, AHE in this compound remains significantly large in the whole range of $\delta$ because of the robust nature of the topology of bands. To explore the possibility of tuning the anomalous transport effects in Weyl semimetals, we have studied the single-crystal hexagonal-(Mn$_{0.78}$Fe$_{0.22}$)$_3$Ge compound. Magnetization of this compound shows two magnetic transitions at 242 K ($T_{\text{N1}}$) and 120 K ($T_{\text{N2}}$). We observed that the AHE persists between $T_{\text{N2}}$ - $T_{\text{N1}}$ and vanishes below $T_{\text{N2}}$. Further, we performed single-crystal neutron diffraction experiments (using spherical neutron polarimetry and unpolarized neutron diffraction) to determine the magnetic structures of (Mn$_{0.78}$Fe$_{0.22}$)$_3$Ge at different temperatures. Our neutron diffraction results show that the sample possesses a collinear antiferromagnetic structure below $T_{\text{N2}}$. However, the magnetic structure of the sample remains noncollinear antiferromagnetic, the same as Mn$_3$Ge, between $T_{\text{N1}}$ to $T_{\text{N2}}$. The presence of AHE, and noncollinear magnetic structure in (Mn$_{0.78}$Fe$_{0.22}$)$_3$Ge, between $T_{\text{N1}}$ and $T_{\text{N2}}$, suggest the existence of Weyl points in this temperature regime. Below $T_{\text{N2}}$, AHE is absent, and the magnetic structure also changes to a collinear antiferromagnetic structure. These observations signify a strong link between the magnetic structure of the sample and AHE.

Machine-learning-assisted automation of single-crystal neutron diffraction

Neutron scattering is a powerful but expensive technique to study materials and discover new matter. Advanced detector technology has significantly improved the efficiency of neutron experiments, increasing the complexity of neutron data reduction and analysis. Machine learning (ML) brings new directions for neutron diffraction data reduction and experiment operation. This work presents an ML-assisted data reduction and analysis method for precise recognition of Bragg peaks and the corresponding regions of interest; it can then automatically screen and align a measured crystal using the recognized peaks, and subsequently plan and optimize the data collection with user-provided information and uncertainty quantification values of detected peaks. This method shows robust performance in different complex sample environments and enables automated single-crystal neutron diffraction.

Magnetic ordering and chirality in multiferroic Dy1-xHoxMnO3 (x = 0.2)

Effect of substitution Dy by Ho on the magneto-electric behavior of the compound Dy0.8Ho0.2MnO3 was investigated by the different methods of polarized and classical neutron diffraction and macroscopic methods. It is shown that substitution by Ho of 20% on the position of Dy do not change overall crystal symmetry of compound. It remains of Pbnm type down to the very low temperatures. Magnetic ordering, its temperature and field evolution was determined by the use of single crystal neutron diffraction and magnetization measurements. Chiral type of magnetic structure on Mn subsystem is confirmed below Tc ≈ 16 K. Using polarized neutron diffraction the 3-component character of rare earth magnetic ordering in Dy0.8Ho0.2MnO3 in contrast to DyMnO3 could be revealed. It was shown that doping by 20% Ho suppresses the spontaneous rare-earth ordering with its own propagation vector and provides the situation when two magnetic subsystems, manganese and rare earth ones have a coherent incommensurate spatial propagation. The influence of the external electric field on the magnetic chirality could be directly evidenced, proving strong magneto-electric coupling in multiferroic phase. The study of the electric polarization under similar temperatures and fields on the same samples provides the direct correlation between the results of the microscopic and macroscopic investigations.