Single-crystal Neutron Diffraction Study Research Articles

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

Single-crystal neutron diffraction study on the quasicrystal approximant Au70Al16Tb14

A magnetic order of the quasicrystal approximant Au70Al16Tb14 was investigated via single crystalline neutron diffraction experiments. In spite of some differences in the macroscopic magnetic properties compared with Au72Al14Tb14, the whirling antiferromagnetic structure similar to Au72Al14Tb14 was found. The robustness of the magnetic structure suggests the orientation of the magnetic moment dominated by easy-axis anisotropy of Tb. In addition, the critical exponent β indicates a mean field nature of the magnetic transition.

Evidence of correlated incommensurate structural and magnetic order in highly oxygen-doped layered nickelate Nd2NiO4.23

$\mathrm{Nd}{}_{2}\mathrm{NiO}{}_{4+\ensuremath{\delta}}$ is a nonstoichiometric oxide, crystallizing in the Ruddlesden-Popper-type framework and exhibiting a wide range of oxygen nonstoichiometry $\ensuremath{\delta}$ with a complex structural phase diagram. Excess oxygen atoms insert holes, directly influencing the Ni valence state and associated electronic structure. We report here the existence of a correlated incommensurate structural and antiferromagnetic order below $T{}_{N}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 150 K in highly oxygen-doped $\mathrm{Nd}{}_{2}\mathrm{NiO}{}_{4+\ensuremath{\delta}}$ with $\ensuremath{\delta} \ensuremath{\approx}$ 0.23. The crystal and magnetic structures are investigated by polarized and unpolarized single-crystal neutron diffraction studies together with synchrotron x-ray powder diffraction and macroscopic magnetization measurements. Due to the long-range ordering of excess oxygen atoms, the real structure of the compound is incommensurately modulated, represented by $\mathbf{Q}{}_{n}=\ifmmode\pm\else\textpm\fi{}0.813{\mathbf{a}}^{*}\ifmmode\pm\else\textpm\fi{}0.519{\mathbf{b}}^{*}$ wave vectors. The antiferromagnetic order is characterized by the presence of incommensurate Bragg peaks of type ($h\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{4pt}{0ex}}\ensuremath{\varepsilon}$, 0, $l$/2), with $h$ and $l$ being odd-integer numbers and the magnetic incommensurability $\ensuremath{\varepsilon}\ensuremath{\approx}$ 0.36. The in-plane magnetic correlation length is found to be $\ensuremath{\xi}{}_{ab}$ = 184(1) \AA{} but is significantly reduced along the $c$ axis to $\ensuremath{\xi}{}_{c}$ = 39(2) \AA{}, indicating the quasi-two-dimensional nature of the antiferromagnetic correlations. Our study indicates that the excess oxygen atoms nevertheless strongly enhance the magnetic correlations between the ${\mathrm{NiO}}_{2}$ planes, resulting in a doubling of the magnetic unit cell along the $c$ axis. In contrast to $\mathrm{Nd}{}_{2}\mathrm{NiO}{}_{4.1}$, in which the incommensurate periodicity of oxygen and magnetic ordering was found to be identical, the structural and electronic orderings in heavily oxygen-doped ${\mathrm{Nd}}_{2}{\mathrm{NiO}}_{4.23}$ show two independent modulation vectors. Our study thus unravels a strong correlation between structural and electronic orderings in the highly oxygen-doped $\mathrm{Ln}{}_{2}\mathrm{NiO}{}_{4+\ensuremath{\delta}}$ system.

Magnetic structure and spin fluctuations in the colossal magnetoresistance ferrimagnet Mn3Si2Te6

The ferrimagnetic insulator Mn3Si2Te6, which features a Curie temperature Tc at 78 K and a delicate yet consequential magnetic frustration, exhibits colossal magnetoresistance (CMR) when the magnetic field is applied along the magnetic hard axis, surprisingly inconsistent with existing precedents [Y. Ni, H. Zhao, Y. Zhang et al. Phys. Rev. B 103, L161105 (2021)]. This discovery motivates a thorough single-crystal neutron diffraction study in order to gain insights into the magnetic structure and its hidden correlation with the new type of CMR. Here we report a noncollinear magnetic structure below the Tc where the moments lie predominantly within the basal plane but tilt toward the c axis by ~10o at ambient conditions. A substantial magnetic diffuse scattering decays slowly and persists well above the Tc. The evolution of the spin correlation lengths agrees well with the electrical resistivity, underscoring the role of spin fluctuation contributing to the magnetoresistivity near the transition. Application of magnetic field along the c axis, renders a swift occurrence of CMR but only a slow tilting of the magnetic moments toward the c axis. The unparalleled changes indicate a non-consequential role of magnetic polarization.

Possible stripe phases in the multiple magnetization plateaus in TbB4 from single-crystal neutron diffraction under pulsed high magnetic fields

We present a single-crystal neutron diffraction study on the Shastry-Sutherland lattice system TbB$_4$ at zero magnetic field and under pulsed high magnetic fields up to 35 T applied along the crystallographic $c$ axis. While our results confirm the magnetic structures at zero-field as well as those at the half- and full-magnetization plateaus, they offer new insight into the $\frac{2}{9}$- and $\frac{1}{3}$-magnetization plateaus observed in this system. A stripe model of polarized 4-spin-plaquettes whose stripe density proportionally increases with the macroscopic magnetization is in full agreement with the neutron diffraction data. Equally well suited alternative models exist which explain the observed Bragg peaks which are inherently limited in a pulsed high magnetic field experiment. We discuss the different intensity distribution in $Q$ space which can be used to distinguish these models in future experiments.

Weak itinerant magnetic phases of La2Ni7

La2Ni7 is an intermetallic compound that is thought to have itinerant magnetism with a small moment ordering below 65 K. A recent study of single crystal samples by Ribeiro et. al. [Phys. Rev. B 105, 014412 (2022)] determined detailed anisotropic H-T phase diagrams and revealed three zero-field magnetic phase transitions at T1 ~ 61.0 K, T2 ~ 56.5K, and T3 ~ 42 K. In that study only the highest temperature phase is shown to have a clear ferromagnetic component. Here we present a single crystal neutron diffraction study determining the propagation vector and magnetic moment direction of the three magnetically ordered phases, two incommensurate and one commensurate, as a function of temperature. The higher temperature phases have similar, incommensurate propagation vectors, but with different ordered moment directions. At lower temperatures the magnetic order becomes commensurate with magnetic moments along the c direction as part of a first-order magnetic phase transition. We find that the low-temperature commensurate magnetic order is consistent with a proposal from earlier DFT calculations.

Site Mixing for Engineering Magnetic Topological Insulators

The van der Waals compound, MnBi$_2$Te$_4$, is the first intrinsic magnetic topological insulator, providing a materials platform for exploring exotic quantum phenomena such as the axion insulator state and the quantum anomalous Hall effect. However, intrinsic structural imperfections lead to bulk conductivity, and the roles of magnetic defects are still unknown. With higher concentrations of same types of magnetic defects, the isostructural compound MnSb$_2$Te$_4$ is a better model system for a systematic investigation of the connections among magnetic, topology and lattice defects. In this work, the impact of antisite defects on the magnetism and electronic structure is studied in MnSb$_2$Te$_4$. Mn-Sb site mixing leads to complex magnetic structures and tunes the interlayer magnetic coupling between antiferromagnetic and ferromagnetic. The detailed nonstoichiometry and site-mixing of MnSb$_2$Te$_4$ crystals depend on the growth parameters, which can lead to $\approx$40\% of Mn sites occupied by Sb and $\approx$15\% of Sb sites by Mn in as-grown crystals. Single crystal neutron diffraction and electron microscopy studies show nearly random distribution of the antisite defects. Band structure calculations suggest that the Mn-Sb site-mixing favors a FM interlayer coupling, consistent with experimental observation, but is detrimental to the band inversion required for a nontrivial topology. Our results suggest a long range magnetic order of Mn ions sitting on Bi sites in MnBi$_2$Te$_4$. The effects of site mixing should be considered in all layered heterostructures that consist of alternating magnetic and topological layers, including the entire family of MnTe(Bi$_2$Te$_3$)$_n$, its Sb analogs and their solid solution.

Flux Synthesis of a Metal Carbide Hydride Using Anthracene As a Reactant.

La15(FeC6)4H was synthesized from the reaction of iron and anthracene in La/Ni eutectic flux. Anthracene was the source of both the carbon and hydrogen in the product. The structure of this metal carbide hydride features hydride ions in tetrahedral interstitial sites surrounded by lanthanum ions, which was confirmed by single-crystal neutron diffraction studies. The trigonal planar FeC6 units in which the central iron atom is coordinated by three ethylenide groups are similar to those found in La3.67FeC6, a previously reported compound that is formed in the absence of a hydride source. Magnetic susceptibility data confirm that the iron sites do not have magnetic moments. Density of states calculations indicate that La15(FeC6)4H is metallic and is stabilized by the incorporation of hydride anions.

Polyhydrido Copper Nanoclusters with a Hollow Icosahedral Core: [Cu30 H18 {E2 P(OR)2 }12 ] (E=S or Se; R=nPr, iPr or iBu).

Although atomically precise polyhydrido copper nanoclusters are of prime interest for a variety of applications, they have so far remained scarce. Herein, this work describes the synthesis of a dithiophosphate-protected copper(I) hydride-rich nanocluster (NC), [Cu30 H18 {S2 P(OnPr)2 }12 ] (1H ), fully characterized by various spectroscopic methods and single-crystal X-ray diffraction. The X-ray structure of 1H reveals an unprecedented central Cu12 hollow icosahedron. Six faces of this icosahedron are capped by Cu3 triangles, the whole Cu30 core being wrapped by twelve dithiophosphate ligands and the whole cluster has ideal S6 symmetry. The locations of the 18 hydrides in 1H were ascertained by a single-crystal neutron diffraction study. They are composed of three types: capping μ3 -H, interstitial μ4 -H (seesaw) and μ5 -H ligands (square pyramidal), in good agreement with the DFT simulations. The numbers of hydrides and ligand resonances in the 1 H NMR spectrum of 1H are in line with their coordination environment in the solid state, retaining the S6 symmetry in solution. Furthermore, two new Se-protected polyhydrido copper nanoclusters, [Cu30 H18 {Se2 P(OR)2 }12 ] (2H : R=iPr 3H : R=iBu) were synthesized from their sulfur relative 1H via ligand displacement reaction and their X-ray structures feature the exceptional case where both the NC shape and size are fully conserved during the course of ligand exchange. DFT and TD-DFT calculations allow understanding the bonding and optical properties of clusters 1H -3H . In addition, the reaction of 1H with [Pd(PPh3 )2 Cl2 ] in the presence of terminal alkynes led to the formation of new bimetallic Cu-Pd alloy clusters [PdCu14 H2 {S2 P(OnPr)2 }6 (C≡CR)6 ] (4: R=Ph; 5: R=C6 H4 F).

The incommensurately modulated structures of low-temperature labradorite feldspars: a single-crystal X-ray and neutron diffraction study.

Labradorite feldspars of the plagioclase solid solution series have been known for their complicated subsolidus phase relations and enigmatic incommensurately modulated structures. Characterized by the irrationally indexed e-reflections in the diffraction pattern, e-labradorite shows the largest variation in the incommensurate ordering states among the e-plagioclase structures. The strongly ordered low-temperature e-labradorite is one of the last missing pieces of the e-plagioclase puzzle. Nine plutonic and metamorphic labradorite feldspar samples from Canada, Ukraine, Minnesota (USA), Tanzania and Greenland with compositions ranging from An52.5 to An68 were studied with single-crystal X-ray diffraction. Two crystals from Labrador, Canada, and Duluth, MN, USA, with wide enough twin lamellae were analyzed with single-crystal neutron diffraction. The incommensurately modulated structures of e-plagioclase are refined for the first time with neutron diffraction data, which confirmed that the T-O distance modulation in the low-temperature e-plagioclase results from the Al-Si ordering in the framework. Detailed configurations of the M site are also observed in the structures refined from neutron diffraction data, which were not possible to see with X-ray diffraction data. The relation between the q-vectors and the mole% An composition is revealed for the entire compositional range of e-plagioclase, from An25 to An75. The previously proposed two-trend relation depending on the cooling rate and phase transition path is confirmed. A new classification of e-plagioclase (eα, eβ and eγ) is proposed based on the q-vector of the structure, which makes it an independent character from the presence/absence of density modulation. New parameters are proposed to quantify the ordering states of these complicated aperiodic structures of e-plagioclases, such as the difference between 〈T1o-O〉 and 〈T1m-O〉 at phase t = 0.2 or the normalized intensity of the (071\bar 1) reflection.

Commensurate to incommensurate magnetic phase transition in honeycomb-lattice pyrovanadateMn2V2O7

We have synthesized single crystalline sample of Mn$_2$V$_2$O$_7$ using floating zone technique and investigated the ground state using magnetic susceptibility, heat capacity and neutron diffraction. Our magnetic susceptibility and heat capacity reveal two successive magnetic transitions at $T_{N1} =$ 19 K and $T_{N2} =$ 11.8 K indicating two distinct magnetically ordered phases. The single crystal neutron diffraction study shows that in the temperature ($T$) range 11.8 K $\le T \le$ 19 K the magnetic structure is commensurate with propagation vector $k_1 = (0, 0.5, 0)$, while upon lowering temperature below $T_{N2} =$ 11.8 K an incommensurate magnetic order emerges with $k_2 = (0.38, 0.48, 0.5)$ and the magnetic structure can be represented by cycloidal modulation of the Mn spin in $ac-$plane. We are reporting this commensurate to incommensurate transition for the first time. We discuss the role of the magnetic exchange interactions and spin-orbital coupling on the stability of the observed magnetic phase transitions.

Insights on the Jahn–Teller distortion, hydrogen bonding and local-environment correlations in a promised multiferroic hybrid perovskite

Perovskite-type formates have recently emerged as potential candidates for multiferroics. Previous ab initio calculations have concluded that copper guanidinium formate (CuGF) is a promising multiferroic. Although ab initio design and characterisation of inorganic multiferroics is at a mature stage, this situation is not true for multiferroic metal-organic frameworks. Regardless of these limitations, such predictions have also been extended to other materials. Here, we present with deeper insights into the structural aspects based on single crystal neutron diffraction studies, questioning such predictions in CuGF. The comparative investigation of the polar CuGF and its centrosymmetric cousin, MnGF, uncovers the differences in the N–H⋯O bonds. Such differences are associated with the Jahn–Teller distortion, which balances its influence on the local-environment of the three sets of ND2 in the guanidinium cation. Hydrogen bonds which were not dealt with in the previous ab initio studies have been carefully treated in this experimental study. Hence, providing a crucial understanding based on which an encouraging platform may be rendered for improving the ab initio calculations for hybrid perovskites catering various applications.

Magnetic phase diagram of the quantum spin chain compound SrCo2V2O8: a single-crystal neutron diffraction study

We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector = (0, 0, 1) develops below TN ≃ 5.0 K. Applying an external magnetic field (H∥c axis) destabilizes this C-AFM order, leading to an order-disorder transition between TN and ∼1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM) transition occurs at 3.9 T, above which the magnetic reflections can be indexed by = (0, 0, 1 ± δl). The incommensurability δl scales monotonically with H until the IC-AFM order disappears around 7.0 T. Magnetic reflections modulated by emerge again at higher fields. While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Néel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.

H-bonding in lazulite: a single-crystal neutron diffraction study at 298 and 3 K

The crystal structure and crystal chemistry of a lazulite from Crosscut Creek (Kulan Camp area, Dawson mining district, Yukon, Canada) was investigated by electron microprobe analysis in wavelength-dispersive mode (EMPA) and single-crystal neutron diffraction at 298 and 3 K. Its empirical formula, based on EMPA data, is: (Mg0.871Fe0.127)Σ0.998Al2.030(P1.985Ti0.008Si0.007O4)2(OH)2. The neutron diffraction experiments at room and low T proved that the H-free structural model of lazulite previously reported, on the basis of X-ray structure refinement, is correct: the building unit of the lazulite structure consists of a group of three face-sharing (Al-octahedron) + (Mg,Fe-octahedron) + (Al-octahedron), connected to the adjacent one via a corner-shared OH-group and two corner-shared oxygen sites of the P-tetrahedron, to form a dense 3D-edifice. Only one crystallographically independent H site occurs in the structure of lazulite, forming a hydroxyl group with the O5 oxygen, with O5–H = 0.9997 A at room temperature (corrected for riding motion effect). The H-bonding scheme in the structure of lazulite is now well defined: a bifurcated bonding scheme occurs with the O4 and O2 oxygen sites as acceptors. The two H-bonds are energetically different, as shown by their bonding geometry: the H-bond with the O2 site as acceptor is energetically more favorable, being O5–H···O2 = 152.67(9)°, O5···O2 = 3.014(1) A and H···O2 = 2.114(1) A, whereas that with O4 as acceptor is energetically more costly, being O5–H···O4 = 135.73(8)°, O5···O4 = 3.156(1) A and H···O4 = 2.383(1) A, at room temperature. No T-induced phase transition occurs within the T-range investigated. At low temperature, the O5–H···O2 bond is virtually identical to the room-T one, whereas the effects of T on O5–H···O4 are more pronounced, with significant differences of the Odonor···Oacceptor and H···Oacceptor distances. The experimental findings of this study do not support the occurrence of HPO4 or H2PO4 units into the structure of lazulite, recently reported on the basis of infrared and Raman spectra.

A single-crystal neutron diffraction study on magnetic structure of CsCo2Se2**Project supported by the National Basic Research Program of China (Grant No. 2012CB921700), the National Natural Science Foundation of China (Grant No. 11190024), the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grant Nos. 17XNLF04 and 17XNLF06). J.S. acknowledges support from China

The magnetic structure of CsCo2Se2 was investigated using single-crystal neutron diffraction technique. An antiferromagnetic transition with the propagation vector (0,0,1) was observed at TN = 78 K. The Co magnetic moment 0.772(6) μB at 10 K pointing in the basal plane couples ferromagnetically in the plane, which stacks antiferromagnetically along the c direction. Tuning and suppressing the interplane antiferromagnetic interaction may be crucial to induce a superconducting state in the material.

Single-crystal neutron diffraction study of hexagonal multiferroic YbMnO3 under a magnetic field

We report single-crystal neutron diffraction study of the magnetic structure of the multiferroic compound YbMnO$_3$, a member of the hexagonal manganite family, in zero-field and under a magnetic field applied along the $c$-axis. We propose a scenario for the zero-field magnetic ordering and for the field-induced magnetic reorientation of the Mn and of the two Yb on distinct crystallographic sites, compatible with the macroscopic measurements, as well as with previous powder neutron diffraction experiment and results from other techniques (optical second harmonic generation, M\"ossbauer spectroscopy). Our study should contribute in settling some debated issues about the magnetic properties of this material, as part of a broader investigation of the entire hexagonal RMnO$_3$ (R = Dy, Ho, Er, Tm, Yb, Lu, Y) family.

On the labyrinthine world of arsenites: a single-crystal neutron and X-ray diffraction study of cafarsite

The crystal chemistry of a cafarsite sample from the fengitic orthogneisses of the Mt. Leone-Arbola nappe (Lower Penninic), forming the central body of Mount Cervandone and cropping out both in Switzerland and Italy (Alpe Devero area, Verbano–Cusio–Ossola province), was investigated by electron microprobe analysis in wavelength-dispersive mode (EPMA-WDS), single-crystal Raman spectroscopy, and single-crystal X-ray and neutron diffraction at 293 K. The sample of cafarsite of this study was found experimentally to be anhydrous and the chemical formula obtained on the basis of the EPMA-WDS data and structural refinements is the following: Ca1,Ca2(Ca15.56Na0.44)Σ16Fe1(Na0.53Fe2+0.17REE0.30)Σ1.00Mn1,Ti,Fe2(Ti7.46Fe3+4.47Fe2+3.20Mn2+0.85Al0.11) Σ16.11As1,As2,As3(AsO3)28 FF, with the general chemical formula Ca16(Na,Fe2+,REE)(Ti, Fe3+,Fe2+,Mn2+,Al)16(AsO3)28F [or Ca16(Na,Fe2+,REE)(Ti,Fe3+,Al)12(Fe2+,Mn)4(AsO3)28F]. Our experimental findings show that fluorine, which was unconsidered in the previous studies, is a key element. The anhydrous nature of this sample is also confirmed by its Raman spectrum, which does not show any evidence of active bands ascribable to the O–H stretching region. The X-ray and neutron structure refinements provide a structure model that is partially in agreement with the previous experimental findings. The space group (i.e. Pn3) and the unit-cell constant [i.e. 15.9507(4) A] are conform to the literature data, but the structure of cafarsite, here refined, contains the following building units: three independent AsO3 groups (trigonal pyramids), one CaO6F polyhedron, one CaO8 polyhedron, two independent (Ti,Fe)O6 octahedra, one (Na,Fe,REE)O8 polyhedron, and one (Mn,Fe)O6 octahedron. Connections among polyhedra are mainly due to edge- or vertex-sharing; the AsO3 groups are not connected to each other.

A single crystal neutron diffraction study on mixed crystal $$\hbox {(K)}_{0.25}(\hbox {NH}_{4})_{0.75}\hbox {H}_{2}\hbox {PO}_{4}$$ (K) 0.25 ( NH 4 ) 0.75 H 2 PO 4 : tuning of short strong hydrogen bonds by ionic interactions

One of the most intriguing facts about hydrogen bonds is that bonds formed between the same couple of donor and acceptor atoms can have large variation in the geometry as well as energies; this is mainly because hydrogen bonds are highly sensitive to their environment. We report here a comparative study of neutron structures of mixed crystals of potassium–ammonium dihydrogen phosphate. Basic structural framework of crystals belonging to potassium dihydrogen phosphate family is constructed by a network of zigzag O–H–O hydrogen bonded chains of \(\hbox {PO}_{2}\hbox {(OH)}_{2}\) anions, with cations occupying the interspaces of the zigzagged anionic chains. These crystals having simple crystal structure primarily determined by the O–H–O hydrogen bonds connecting \(\hbox {PO}_{2}\hbox {(OH)}_{2}\) anions provide us with a unique opportunity to tune the hydrogen bond geometry by varying the cationic occupancy and study the effect of this change on the average structure of the crystal. The cation–anion interaction is found to have a direct influence on the O–H–O hydrogen bonds of the mixed crystals.

Soft antiphase tilt of oxygen octahedra in the hybrid improper multiferroic Ca3Mn1.9Ti0.1O7

We report a single crystal neutron and x-ray diffraction study of the hybrid improper multiferroic Ca3Mn1.9Ti0.1O7 (CMTO), a prototypical system where the electric polarization arises from the condensation of two lattice distortion modes.With increasing temperature (T ), the out-of-plane, antiphase tilt of MnO6 decreases in amplitude while the in-plane, in-phase rotation remains robust and experiences abrupt changes across the first-order structural transition. Application of hydrostatic pressure (P) to CMTO at room temperature shows a similar effect. The consistent behavior under both T and P reveals the softness of antiphase tilt and highlights the role of the partially occupied d orbital of the transition-metal ions in determining the stability of the octahedral distortion. Polarized neutron analysis indicates the symmetry-allowed canted ferromagnetic moment is less than the 0.04 {\mu}B/Mn site, despite a substantial out-of-plane tilt of the MnO6 octahedra.

High oxide-ion conductivity in Si-deficient La9.565(Si5.826□0.174)O26apatite without interstitial oxygens due to the overbonded channel oxygens

Overbonding of the channel oxygens in the apatite-type lanthanum silicates was found to be a key for the high oxide-ion conductivities by the present single-crystal neutron and X-ray diffraction studies.