Polarized Neutron Diffraction Research Articles

Electric-Field Manipulation of Magnetic Chirality in a Homo-Ferro-Rotational Helimagnet.

Ferro-rotational (FR) materials, renowned for their distinctive material functionalities, present challenges in the growth of homo-FR crystals (i.e., single FR domain). This study explores a cost-effective approach to growing homo-FR helimagnetic RbFe(SO4)2 (RFSO) crystals by lowering the crystal growth temperature below the TFR threshold using the high-pressure hydrothermal method. Through polarized neutron diffraction experiments, it is observed that nearly 86% of RFSO crystals consist of a homo-FR domain. Notably, RFSO displays remarkable stability in the FR phase, with an exceptionally high TFR of ≈573K. Furthermore, RFSO exhibits a chiral helical magnetic structure with switchable ferroelectric polarization below 4K. Importantly, external electric fields can induce a single magnetic domain state and manipulate its magnetic chirality. The findings suggest that the search for new FR magnets with outstanding material properties should consider magnetic sulfates as promising candidates.

Magnetic Helicity in a Chiral‐Polar Magnet Ni2InSbO6

The class of chiral‐polar magnets has recently captured significant interest in scientific study due to their intriguing physical phenomena. Among all the chiral‐polar magnets, Ni2InSbO6 stands out because of its unique attributes, such as the emergence of the topological chiral soliton lattice in the presence of an external magnetic field perpendicular to the chiral‐polar axis. However, the magnetic structure of Ni2InSbO6 at zero field has not been well understood yet. This work presents an analysis including polarized optical microscopy and polarized neutron diffraction on a carefully chosen Ni2InSbO6 crystal. Results confirm the predominance of a single chiral‐polar domain within the crystal and indicate the likelihood of cycloidal magnetic ordering under zero magnetic field, alongside the observation of net magnetic helicity. The existence of both a dominant chiral‐polar domain and a dominant cycloidal magnetic domain within Ni2InSbO6 provides an excellent platform for further exploration of its unconventional physical attributes.

Magnetic defect characterization by polarized neutron diffraction

Magnetic defect characterization by polarized neutron diffraction

Magneto-structural relationships in coordination compounds – a polarized neutron diffraction vision

Magneto-structural relationships in coordination compounds – a polarized neutron diffraction vision

Polarised neutron scattering from dynamic polarised nuclei 1972–2022

With the inauguration of the small-angle instrument D11 of the Institute Laue–Langevin (ILL) in September 1972 neutron scattering revolutionized methods of contrast variation. Very soon D11 was oversubscribed by proposals relying on isotopic substitution of hydrogen isotopes. At the same time in Oxford first experiments of polarised neutron diffraction from dynamic polarised protons in lanthanum magnesium nitrate crystals demonstrated the great utility of this approach. In the early eighties a new type of polarised target material led to a boom of contrast variation by nuclear polarisation. The new samples of frozen solutions of macromolecules lent themselves to small-angle scattering. Often in collaboration with research centres of High Energy Physics various groups in Europe and Japan started experiments of polarized neutron scattering from dynamic polarised protons. Techniques of NMR and EPR considerably enlarged the spectrum of nuclear contrast variation. This is shown with time-resolved polarised neutron scattering from dynamic polarized proton spins of a free radical and of tyrosyl doped catalase using D22 at the ILL.Graphical abstract

The first polarized neutron diffraction experiment at the time-of-flight single crystal neutron diffractometer SENJU at J-PARC

The 3He spin filter has been developed to use pulsed neutrons effectively at J-PARC MLF. In this study, the 3He spin filter was installed in the single crystal neutron diffractometer (BL18 SENJU) at J-PARC MLF as a polarizer of the incident beam, and Half-polarized neutron diffraction experiments were performed. The 3He spin filter was used the ”drop-in cell” method with cells that had a relaxation time of 150 hours in the past experiments. The sample was a single crystal of Heusler crystal Cu2MnAl and the sample magnetic field was 0.3 T. The intensities of (111) Bragg peaks of Cu2MnAl were drastically changed with the polarity of the incident neutron beam, and the flipping ratio of 21.7 at 3.6 Å was observed. The experimental setup and the performance of the 3He spin filter used in this experiment are described in detail in this paper.

Nanoscale structure of a hybrid aqueous-nonaqueous electrolyte.

A new class of electrolytes have been reported, hybridizing aqueous with non-aqueous solvents, which combines non-flammability and non-toxicity characteristics of aqueous electrolytes with the superior electrochemical stability of non-aqueous systems. Here, we report measurements of the structure of an electrolyte composed of an equal-mass mixture of 21m LiTFSI-water and 9m LiTFSI-dimethyl carbonate using high-energy x-ray diffraction and polarized neutron diffraction with isotope substitution. Neutron structure factors from partially and fully deuterated samples exhibit peaks at low scattering vector Q that we ascribe to long-range correlations involving both solvent molecules and TFSI- anions. We compare both sets of measurements with results of molecular dynamics simulations based on a polarizable force field. The structures derived from simulations are generally in agreement with those measured, except that neutron structure factors predicted for two partially deuterated samples show very intense scattering increasing up to the low-Q limit of simulation, indicating a partial segregation between the two solvents not observed in experimental measurements.

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.

Determining Local Magnetic Susceptibility Tensors in Paramagnetic Lanthanide Crystalline Powders from Solid-State NMR Chemical Shift Anisotropies

Exploring magnetic properties at the molecular level is a challenge that has been met by developing many experimental and theoretical solutions, such as polarized neutron diffraction (PND), muon-spin rotation (μ-SR), electron paramagnetic resonance (EPR), SQUID-based magnetometry measurements, and advanced modeling on open-shell systems and relativistic calculations. These methods are powerful tools that shed light on the local magnetic response in specifically designed magnetic materials such as contrast agents, for MRI, molecular magnets, magnetic tags for biological NMR, etc. All of these methods have their advantages and disadvantages. In order to complement the possibilities offered by these methods, we propose a new tool that implements a new approach combining simulation and fitting for high-resolution solid-state NMR spectra of lanthanide-based paramagnetic species. This method relies on a rigorous acquisition thanks to short high-power adiabatic pulses (SHAP) of high-resolution solid-state NMR isotropic and anisotropic data on a powdered magnetic material. It is also based on an efficient modeling of this data thanks to a semiempirical model based on a parametrization of the local magnetism and the crystal structure provided by diffraction methods. The efficiency of the calculation relies on a thorough simplification of the electron-nucleus interactions (point-dipole interaction, no Fermi contact) which is validated by experimental analysis. By taking advantage of the efficient calculation possibilities offered by our method, we can compare a great number of simulated spectra to experimental data and find the best-matching local magnetic susceptibility tensor. This method was applied to a series of isostructural lanthanide oxalates which are used as a benchmark system for many analytical methods. We present the results of thorough solid-state NMR and extensive modeling of the hyperfine interaction (including up to 400 paramagnetic centers) that yield local magnetic susceptibility tensor measurements that are self-consistent as well as consistent with bulk susceptibility measurements.

Canted ferromagnetic order in nonsuperconducting Eu(Fe1−xNix)2As2

The magnetic order in a series of nonsuperconducting $\mathrm{Eu}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{2}{\mathrm{As}}_{2}$ single crystals is investigated in detail by polarized neutron diffraction. The Fe and Eu magnetic sublattices are found to be almost magnetically decoupled in this system. With the Ni doping, the Eu sublattice shows a dramatic change in its magnetic ground state, from the A-type antiferromagnetic order for $\mathit{x}\ensuremath{\le}0.02$, in which the spins lie in the $\mathit{ab}$ plane, to a pure canted ferromagnetic order for $0.04\ensuremath{\le}\mathit{x}\ensuremath{\le}0.20$, in which the spins are canted with a small angle off the $\mathit{c}$ axis. By comparison with the $\mathit{c}$-axis perfectly aligned ferromagnetic structure widely observed in other superconducting compounds, the lack of superconductivity in $\mathrm{Eu}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{2}{\mathrm{As}}_{2}$ might be associated with the formation of in-plane ferromagnetism. The doping-induced change of the lattice constants and accordingly the variation of the strength of indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the ${\mathrm{Eu}}^{2+}$ moments is speculated to be responsible for the dramatic change of the Eu spin structure. In addition, a spin reorientation of the ${\mathrm{Eu}}^{2+}$ moments in an intermediate temperature range is observed for $\mathit{x}=0.20$, in which some in-plane spin fluctuations persists above the long-range ordering temperature ${T}_{\mathrm{Eu}}$.

Multi-Technique Experimental Benchmarking of the Local Magnetic Anisotropy of a Cobalt(II) Single-Ion Magnet.

A comprehensive understanding of the ligand field and its influence on the degeneracy and population of d-orbitals in a specific coordination environment are crucial for the rational design and enhancement of magnetic anisotropy of single-ion magnets (SIMs). Herein, we report the synthesis and comprehensive magnetic characterization of a highly anisotropic CoII SIM, [L2Co](TBA)2 (L is an N,N'-chelating oxanilido ligand), that is stable under ambient conditions. Dynamic magnetization measurements show that this SIM exhibits a large energy barrier to spin reversal U eff > 300 K and magnetic blocking up to 3.5 K, and the property is retained in a frozen solution. Low-temperature single-crystal synchrotron X-ray diffraction used to determine the experimental electron density gave access to Co d-orbital populations and a derived U eff, 261 cm-1, when the coupling between the d x 2-y 2 and dxy orbitals is taken into account, in very good agreement with ab initio calculations and superconducting quantum interference device results. Powder and single-crystal polarized neutron diffraction (PNPD, PND) have been used to quantify the magnetic anisotropy via the atomic susceptibility tensor, revealing that the easy axis of magnetization is pointing along the N-Co-N' bisectors of the N,N'-chelating ligands (3.4° offset), close to the molecular axis, in good agreement with complete active space self-consistent field/N-electron valence perturbation theory to second order ab initio calculations. This study provides benchmarking for two methods, PNPD and single-crystal PND, on the same 3d SIM, and key benchmarking for current theoretical methods to determine local magnetic anisotropy parameters.

Hidden magnetic texture in the pseudogap phase of high-Tc YBa2Cu3O6.6

Despite decades of intense research, the enigmatic pseudo-gap (PG) phase of superconducting cuprates remains unsolved. In the last 15 years, various symmetry breaking states were discovered in the PG phase, including an intra-unit cell (IUC) magnetism, which preserves the lattice translational (LT) symmetry but breaks the time-reversal and parity symmetries, and an additional incipient charge density wave breaking the LT symmetry. However, none of these states can (alone) account for the partial gapping of the Fermi surface. Here we report a hidden LT-breaking magnetism using polarized neutron diffraction. Our measurements reveal magnetic correlations, in two different underdoped YBa2Cu3O6.6 single crystals that set in at the PG onset temperature with (i) a planar propagation wave vector (π, 0) ≡ (0, π), yielding a doubling or quadrupling of the magnetic unit cell and (ii) magnetic moments mainly pointing perpendicular to the CuO2 layers. The LT-breaking magnetism is at short-range suggesting the formation of clusters of 5–6 unit cells. Together with the previously reported IUC magnetism, it yields a hidden magnetic texture of the CuO2 unit cells hosting loop currents, forming large supercells that may be helpful for elucidating the PG puzzle.

Polar magnetization unveiled by polarized neutron diffraction

Polar magnetism is present when ions occupy sites that are not centres of inversion symmetry. Fortunately, such magnetization contributes to neutron scattering that is the bedrock of magnetic structure determinations. Experiments in which the scattered neutron polarization is analysed are not a novelty. Simulations of polarized neutron scattering amplitudes for room temperature haematite (alpha-Fe2O3) demonstrate the wealth of information on offer. Two magnetic motifs distinguished by the orientation of their bulk ferromagnetism are considered. Additionally, the symmetry-inspired simulations challenge a recent claim to have determined the absolute direction of the Dzyaloshinskii-Moriya (D-M) interaction.

Loop currents in quantum matter

In many quantum materials, strong electron correlations lead to the emergence of new states of matter. In particular, the study in the last decades of the complex phase diagram of high temperature superconducting cuprates highlighted intra-unit-cell electronic instabilities breaking discrete Ising-like symmetries, while preserving the lattice translation invariance. Polarized neutron diffraction experiments have provided compelling evidences supporting a new form of intra-unit-cell magnetism, emerging concomitantly with the so-called pseudogap state of these materials. This observation is currently interpreted as the magnetic hallmark of an intra-unit-cell loop current order, breaking both parity and time-reversal symmetries. More generally, this magneto-electric state is likely to exist in a wider class of quantum materials beyond superconducting cuprates. For instance, it has been already observed in hole-doped Mott insulating iridates or in the spin liquid state of hole-doped 2-leg ladder cuprates.

Asphericity of magnetization density and anisotropy in rare-earth pyrochlores via polarized neutron diffraction and iterative entropy maximization

The procedure of magnetization density reconstruction in locally anisotropic magnetics with unquenched orbital moment is developed, based on the iterative entropy maximization and the site susceptibility approach. The procedure provides simultaneously model-free site susceptibility parameters of the $R$ ions and the shape of the magnetization distribution. The reconstruction of a noncollinear magnetic moment distribution was applied to rare-earth pyrochlore compounds ${R}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ $(R=\text{Tb}, \mathrm{Ho}, \mathrm{Er}, \mathrm{Yb})$, which revealed an oblate asphericity of the ${\mathrm{Tb}}^{3+}$ magnetization density and a prolate one for the ${\mathrm{Ho}}^{3+}$ and ${\mathrm{Yb}}^{3+}$ ions. The noncollinear magnetic moment distributions are compared with these predicted by the single-ion anisotropy model, shedding light on the anisotropy of lanthanides with an unquenched orbital moment.

Structural studies of 1H-containing liquids by polarized neutrons: Chemical environment and wavelength dependence of the incoherent background

Following a demonstration of how neutron diffraction with polarization analysis may be applied for the accurate determination of the coherent static structure factor of disordered materials containing substantial amounts of proton nuclei (Temleitner et al., Phys. Rev. B 92, 014201, 2015), we now focus on the incoherent scattering. Incoherent contributions are responsible for the great difficulties while processing standard (non-polarized) neutron diffraction data from hydrogenous materials, hence the importance of the issue. Here we report incoherent scattering intensities for liquid acetone, cyclohexane, methanol and water, as function of the 1H/H ratio. The incoherent intensities are determined directly by polarized neutron diffraction. This way, possible variations of the incoherent background due to the changing chemical environment may be monitored. In addition, for some of the water samples, incoherent intensities as a function of the wavelength of the incident neutron beam (at 0.4, 0.5 and 0.8 Å) have also been measured. It is found that in each case, the incoherent intensity can be described by a single Gaussian function, within statistical errors. The (full) width (at half maximum) of the Gaussians clearly depends on the applied wavelength. On the other hand, the different bonding environments of hydrogen atoms do not seem to affect the width of the Gaussian.

Polarized Neutron Diffraction: An Excellent Tool to Evidence the Magnetic Anisotropy—Structural Relationships in Molecules

This publication reviews recent advances in polarized neutron diffraction (PND) studies of magnetic anisotropy in coordination compounds comprising d or f elements and having different nuclearities. All these studies illustrate the extent to which PND can provide precise and direct information on the relationship between molecular structure and the shape and axes of magnetic anisotropy of the individual metal sites. It makes this experimental technique (PND) an excellent tool to help in the design of molecular-based magnets and especially single-molecule magnets for which strong uniaxial magnetic anisotropy is required.

Magnetic structure of the topological semimetal YbMnSb2

Recently, the antiferromagnet YbMnSb${}_{2}$ has been predicted to be a topological semimetal driven by time-reversal symmetry breaking, where the magnetic order is key to its behavior as a topological material. Depending on the magnetic order, YbMnSb${}_{2}$ can have Weyl, nodal-line, or Dirac topological features. In this Letter, the authors use a combination of unpolarized and polarized neutron diffraction to determine unambiguously the magnetic structure of YbMnSb${}_{2}$ and the topology of the electronic bands.

Spin-resolved charge density and wavefunction refinements using MOLLYNX: a review

MOLLYNX is a new crystallographic tool developed to access a more precise description of the spin-dependent electron density of magnetic crystals, taking advantage of the richness of experimental information from high-resolution X-ray diffraction (XRD), unpolarized neutron (UND) and polarized neutron diffraction (PND). This new program is based either on the well known Hansen–Coppens multipolar model (MOLLYNX-mult) or on a new expansion over a set of atomic orbitals (MOLLYNX-orb). The main difference between the two models is the basis of the expansion: in MOLLYNX-mult the expansion is over atom centered real spherical harmonics, in MOLLYNX-orb the expansion is over a set of atomic orbitals with which mono and bicentric contributions are calculated. This new approach of MOLLYNX-orb can also be applied to nonmagnetic crystals. This paper summarizes the theoretical ground of two models and describes the first applications to organic, organometallic and inorganic magnetic materials

Quantifying magnetic anisotropy using X-ray and neutron diffraction

In this work, the magnetic anisotropy in two iso-structural distorted tetrahedral Co(II) complexes, CoX 2tmtu2 [X = Cl(1) and Br(2), tmtu = tetra-methyl-thio-urea] is investigated, using a combination of polarized neutron diffraction (PND), very low-temperature high-resolution synchrotron X-ray diffraction and CASSCF/NEVPT2 ab initio calculations. Here, it was found consistently among all methods that the compounds have an easy axis of magnetization pointing nearly along the bis-ector of the compression angle, with minute deviations between PND and theory. Importantly, this work represents the first derivation of the atomic susceptibility tensor based on powder PND for a single-molecule magnet and the comparison thereof with ab initio calculations and high-resolution X-ray diffraction. Theoretical ab initio ligand field theory (AILFT) analysis finds the d xy orbital to be stabilized relative to the d xz and d yz orbitals, thus providing the intuitive explanation for the presence of a negative zero-field splitting parameter, D, from coupling and thus mixing of d xy and . Experimental d-orbital populations support this interpretation, showing in addition that the metal-ligand covalency is larger for Br-ligated 2 than for Cl-ligated 1.