Single-crystal Neutron Research Articles

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.

Complex interplay between 3d and 4f magnetic systems in multiferroic DyMnO3

Structural and magnetic properties of single crystals of DyMnO3 were investigated by neutron diffraction in order to study the peculiarities of 3d-4f interactions in this compound. Precise magnetic order and its detailed temperature evolution were determined using single crystal neutron diffraction. Elliptical cycloid on manganese subsystem below TCh = 19 K was confirmed, with temperature decrease the elipticity of the Mn magnetic structure reduces significantly, creating almost circular cycloid. Temperature evolution of the magnetic structure demonstrate specific hysteretic behavior. The results show a complex interplay between transition metal and rare earth magnetic sublattices leading to so-called “Mn- controlled” and “Dy- controlled” magnetic states. The strong and complicate 3d-4f interaction leads to the unusual very slow magnetic structure relaxation.

Incommensurate helimagnetic structure of Ba(Fe1−xScx)12O19 determined by single-crystal neutron diffraction

Sc-substituted hexagonal ferrite $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$ has an incommensurate helimagnetic structure. However, the incommensurate helimagnetic structure has not been sufficiently determined, and the mechanism via which the helimagnetism develops has not been studied. Time-of-flight-Laue single-crystal neutron diffraction measurements were performed at 4--6 K on single-crystal samples of $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$ having Sc concentrations of $x=0$, 0.128, 0.153, and 0.193. The incommensurate helimagnetic structure was determined by analyzing the magnitude and direction of the ${\mathrm{Fe}}^{3+}$ magnetic moments at the five Fe1--Fe5 sites ($2a, 4e, 4{f}_{1}, 4{f}_{2}$, and $12k$). The development mechanism of the helimagnetic structure was discussed from the standpoint of superexchange interaction. The crystal structure analyses revealed that the Sc substitution enabled two significant events, namely, the coordination changes of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Sc}}^{3+}$ at the $\mathrm{Fe}2(4e)$ site, resulting in the shortened bond distances of Fe2-O1 and the preferred substitution of ${\mathrm{Fe}}^{3+}$ at the $\mathrm{Fe}4(4{f}_{2})$ site with ${\mathrm{Sc}}^{3+}$. The magnetic structure analyses revealed that the helimagnetic structure of $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$ is a cone type whose base is in the $ab$ plane and height is in the $c\text{\ensuremath{-}}\mathrm{axis}$ direction. The magnetic moments of $\mathrm{Fe}2(4e), \mathrm{Fe}4(4{f}_{2})$, and $\mathrm{Fe}5(12k)$ are aligned with distinct angles, leading to the helimagnetic structure of $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$, and can be explained by assuming that there is an antiferromagnetic superexchange interaction ${J}_{5}$ between $\mathrm{Fe}2(4e)$ and $\mathrm{Fe}5(12k)$ that is negligible in the $x=0$ crystal. The shorter bond distance of Fe2-O1 in Sc-rich crystals revealed by the crystal structure analyses enhances the superexchange interaction ${J}_{5}$. However, the ${\mathrm{Sc}}^{3+}$ preference for $\mathrm{Fe}4(4{f}_{2})$ weakens ${J}_{3}$ and ${J}_{4}$. The relatively strong ${J}_{5}$ leads to competition among the three superexchange interactions, ${J}_{3}, {J}_{4}$, and ${J}_{5}$, resulting in the development of the helimagnetic structure. These findings facilitate the understanding of the essentials of the basic magnetic material $\mathrm{Ba}{\mathrm{Fe}}_{12}{\mathrm{O}}_{19}$.

Determination of solubility of cobalt in singlecrystal silicon method neutron activation

Determination of solubility of cobalt in singlecrystal silicon method neutron activation

Observation of proton-transfer-coupled spin transition by single-crystal neutron-diffraction measurement.

The application of single-crystal neutron diffraction (SCND) to observe proton-transfer phenomena in crystalline compounds exhibiting unusual protonation states or proton dynamics has garnered significant research interest in recent years. However, proton tautomerism, which results in different protonation states before and after proton transfer, has never been observed using the SCND technique. Thus, to observe the proton tautomerism phenomenon by SCND measurements, we developed an iron(II) complex that forms a large crystal and exhibits a proton-transfer-coupled spin transition (PCST). The presence of the two types of proton tautomers was determined by conventional analysis of the proton position by X-ray crystallography, infrared spectroscopy, and density functional theory calculations. Finally, our results confirmed that proton tautomerism was successfully observed for the first time using variable-temperature SCND measurements.

Spin and charge density waves in quasi-one-dimensional KMn6Bi5

AMn6Bi5 materials (A = Na, K, Rb and Cs) consisting of unique Mn-cluster chains emerge as a new family of superconductors with the suppression of their antiferromagnetic (AFM) order under high pressures. Here, we report transverse incommensurate spin density waves (SDWs) for the Mn atoms with a propagating direction along the chain axes as a ground state for KMn6Bi5 by single crystal neutron diffraction. The SDWs have a refined amplitude of ~2.46 Bohr magnetons for the Mn atoms in the pentagons and ~0.29 Bohr magnetons with a large standard deviation for Mn atoms in the center between the pentagons. AFM dominate both the nearest-neighbor Mn-Mn interactions within the pentagon and next-nearest-neighbor Mn-Mn interactions out of the pentagon (along the propagating wave). The SDWs exhibit both local and itinerant characteristics probably formed by a cooperative interaction between local magnetic exchange and conduction electrons. A significant magnetoelastic effect during the AFM transition, especially along the chain direction, has been demonstrated by temperature-dependent x-ray powder diffraction. Single crystal x-ray diffraction below the AFM transition revealed satellite peaks originating from charge density waves along the chain direction with a q-vector twice as large as the SDW one, pointing to a strong real space coupling between them. Our work not only manifests a fascinating interplay among spin, charge, lattice and one dimensionality to trigger intertwined orders in KMn6Bi5 but also provides important piece of information for the magnetic structure of the parent compound to understand the mechanism of superconductivity in this new family.

Charge Density Wave in Kagome Lattice Intermetallic ScV_{6}Sn_{6}.

Materials hosting kagome lattices have drawn interest for the diverse magnetic and electronic states generated by geometric frustration. In the AV_{3}Sb_{5} compounds (A=K, Rb, Cs), stacked vanadium kagome layers give rise to unusual charge density waves (CDW) and superconductivity. Here we report single-crystal growth and characterization of ScV_{6}Sn_{6}, a hexagonal HfFe_{6}Ge_{6}-type compound that shares this structural motif. We identify a first-order phase transition at 92K. Single crystal x-ray and neutron diffraction reveal a charge density wave modulation of the atomic lattice below this temperature. This is a distinctly different structural mode than that observed in the AV_{3}Sb_{5} compounds, but both modes have been anticipated in kagome metals. The diverse HfFe_{6}Ge_{6} family offers more opportunities to tune ScV_{6}Sn_{6} and explore density wave order in kagome lattice materials.

Effect of pseudo-Tsai cluster incorporation on the magnetic structures of R−Au−Si (R=Tb,Ho) quasicrystal approximants

In cluster-based quasicrystals, tetrahedra located in conventional Tsai clusters may be replaced by single rare-earth $(R)$ ions at the cluster centers (pseudo-Tsai clusters). In this study, we investigate the effect of the pseudo-Tsai cluster incorporation on the magnetic structures of two approximants, the Tsai-type Tb-Au-Si [denoted TAS(0)] and Ho-Au-Si [denoted HAS(52)] with partial replacement of conventional Tsai clusters by pseudo-Tsai clusters, up to 52%. The mixture of Tsai and pseudo-Tsai clusters can be considered a different source of randomness/disorder other than the conventional chemical mix sites (Au/Si). The effect of the latter has been previously discussed regarding the origin/cause of spin-glass-like ordering and Anderson localization of electronic states in quasicrystals and approximant crystals. Single crystal neutron diffraction experiments at 2 K were performed and bulk physical properties (magnetization and specific heat) were investigated. In addition, earlier collected powder neutron diffraction data of TAS(14) with 14% replacement was reanalyzed in light of the results on TAS(0) and HAS(52). We find that the arrangement of ordered magnetic spins in the icosahedral shells of these phases is similar, while the cluster-center $R$ magnetic states are different. In the case of TAS(14), the cluster-center Tb magnetic moments seem to affect the arrangement of surrounding icosahedral magnetic moments, and the magnetic structure of the icosahedral shell deviates from that of TAS(0). In the case of HAS(52), however, the icosahedral $R$ magnetic moments are less affected by the cluster-center $R$, while the averaged cluster-center $R$ magnetic moments are significantly diminished. We discuss these results considering the magnetic ordering effect on the bulk physical properties.

Unconventional magnetoresistance and electronic transition in Mn3Ge Weyl semimetal

Weyl semimetals are well known for their anomalous transport effects caused by a large fictitious magnetic field generated by the non-zero Berry curvature. We performed the analysis of the electrical transport measurements of the magnetic Weyl semimetal Mn$_{3}$Ge in the a-b and a-c plane. We have observed negative longitudinal magneto-resistance (LMR) at a low magnetic field ($B<1.5$ T) along all the axes. The high field LMR shows different behavior along x and z axes. A similar trend has been observed in the case of planar Hall effect (PHE) measurements as well. The nature of high field LMR along the x axis changes near 200 K. Dominant carrier concentration type, and metallic to semimetallic transition also occur near 200 K. These observations suggest two main conclusions: (i) The high field LMR in Mn$_3$Ge is driven by the metallic - semimetallic nature of the compound. (ii) Mn$_3$Ge compound goes through an electronic band topological transition near 200 K. Single crystal neutron diffraction does not show any change in the magnetic structure below 300 K. However, the in-plane lattice parameter (a) shows a maximum near 230 K. Therefore, it is possible that the change in electronic band structure near 200 K is driven by the a lattice parameter of the compound.

New Insights on the Electronic-Structural Interplay in LaPdSb and CePdSb Intermetallic Compounds.

Multifunctional physical properties are usually a consequence of a rich electronic-structural interplay. To advance our understanding in this direction, we reinvestigate the structural properties of the LaPdSb and CePdSb intermetallic compounds using single-crystal neutron and X-ray diffraction. We establish that both compounds can be described by the non-centrosymmetric space group P63mc, where the Pd/Sb planes are puckered and show ionic order rather than ionic disorder as was previously proposed. In particular, at 300 K, the (h, k, 10)-layer contains diffuse scattering features consistent with the Pd/Sb puckered layers. The experimental results are further rationalized within the framework of DFT and DFT+ embedded DMFT methods, which confirm that a puckered structure is energetically more favorable. We also find strong correspondence between puckering strength and band topology. Namely, strong puckering removes the bands and, consequently, the Fermi surface pockets at the M point. In addition, the Pd-d band character is reduced with puckering strength. Thus, these calculations provide further insights into the microscopic origin of the puckering, especially the correspondence between the band's character, Fermi surfaces, and the strength of the puckering.

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.

Zr3Mn3Sn4Ga: a new hexagonal Ti6Sn5-type quaternary intermetallic

The discovery of a new quaternary intermetallic compound of composition Zr3Mn3Sn4Ga during a survey of the Zr–Mn–Sn–Ga phase diagram is reported. Single-crystal X-ray diffraction reveals that the new compound crystallizes in a hexagonal lattice (space group P63/mmc, No. 194). The analysis of single-crystal X-ray diffraction data indicates that the atomic arrangement is an ordered variant of the high-temperature hexagonal Ti6Sn5 crystal structure. From a simple geometry point of view, the unit cell consists of GaZr3 octahedra chains and Mn chains growing along the sixfold symmetry axis c. The Mn chains are stacked within the ab basal plane in a kagome geometry, with large interatomic distances. The possible slight levels of Sn/Ga and Zr/Mn mixed occupancy based on additional results of electron probe microanalysis and single-crystal neutron diffraction are discussed. It is noteworthy that this compound is the first quaternary intermetallic discovered in this structure and the first Ti6Sn5 derivative bearing a magnetic metal, namely Mn, in the 6g position, which may give rise to interesting physical properties.

Chiral magnetic structure of spin-ladder multiferroic BaFe2Se3

A complex magnetic structure with specific symmetry properties is a relevant ingredient for magnetoelectric multiferroicity. In BaFe${}_{2}$Se${}_{3}$, a member of the Fe spin-ladder family of pressure-induced superconductors, the authors reveal this complexity. Using polarized and unpolarized single-crystal neutron diffraction, they evidence a chiral, umbrella-like magnetic order made of blocks of quasiferromagnetic spins, antiferromagnetically ordered along the ladder. Such accurate information on the magnetism will help to understand the magnetoelectric coupling in this family and its puzzling phase diagram.

Reactivity of a β-diketiminate ytterbium(II) hydride with cyclopentadiene derivatives

Cyclopentadienyl ligands are ubiquitous in lanthanide chemistry and have been used extensively to stabilize low-valent lanthanide(II) complexes. We now report the reactions of the β-diketiminate ytterbium(II) hydride [(BDIDipp)Yb(H)]2 (BDIDipp = HC{C(Me)NDipp}2, Dipp = 2,6- i Pr2C6H3) with tetramethylcyclopentadiene, pentamethylcyclopentadiene, indene, and fluorene; to provide ready access to the heteroleptic ytterbium(II) η5-C5R5 cyclopentadienides with extrusion of hydrogen gas. The tetramethylcyclopentadienyl, pentamethylcyclopentadienyl, indenyl, and fluorenyl compounds were characterized by 1H and 13C{1H} NMR, elemental analysis, and single crystal X-ray diffraction. These data indicated that each heteroleptic cyclopentadienide exists as a mononuclear species in both solution and the solid state, formulated with retention of the oxidation state on the ytterbium(II) center. Additionally, the pentamethylcyclopentadienyl derivative was characterized by single crystal neutron diffraction, a study that explored the nature of an agostic interaction between a methyl group and the ytterbium(II) center.

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.

Structural complexity in the RP phase La2CoO4+δ explored by synchrotron X-ray single-crystal diffraction and neutron powder diffraction

Structural complexity in the RP phase La₂CoO_4+δ explored by synchrotron X-ray single-crystal diffraction and neutron powder diffraction

Structure of high-pressure ices revealed from single-crystal and powder neutron diffraction

Structure of high-pressure ices revealed from single-crystal and powder neutron diffraction

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.

Development update of PIONEER, a single-crystal neutron diffractometer at the Second Target Station, ORNL

Development update of PIONEER, a single-crystal neutron diffractometer at the Second Target Station, ORNL