Low-temperature Neutron Research Articles

Sourcing and reducing sample environment background in low-temperature high-pressure neutron scattering experiments

Neutron scattering in high-pressure environments offers unique opportunities to measure the physical properties of matter but faces challenges due to low signal intensity and high background noise. In this study, Monte Carlo simulations were employed to identify background sources in low-temperature and high-pressure sample environments at the SINQ instrument CAMEA. Simulation results suggest that the piston pressure cell (PC) contributes significantly to the background noise in neutron scattering experiments. To counter this background, a compact radial neutron collimator was developed to reduce background in the sample environment, and its performance was evaluated experimentally. Measurements show that the collimator reduces the background generated by the PC effectively, especially for low q. Noise from the collimator was observed, and strategies to address this issue were discussed.

Noncentrosymmetric Triangular Magnet CaMnTeO6: Strong Quantum Fluctuations and Role of s0 versus s2 Electronic States in Competing Exchange Interactions.

Noncentrosymmetric triangular magnets offer a unique platform for realizing strong quantum fluctuations. However, designing these quantum materials remains an open challenge attributable to a knowledge gap in the tunability of competing exchange interactions at the atomic level. Here, a new noncentrosymmetric triangular S=3/2 magnet CaMnTeO6 is created based on careful chemical and physical considerations. The model material displays competing magnetic interactions and features nonlinear optical responses with the capability of generating coherent photons. The incommensurate magnetic ground state of CaMnTeO6 with an unusually large spin rotation angle of 127°(1) indicates that the anisotropic interlayer exchange is strong and competing with the isotropic interlayer Heisenberg interaction. The moment of 1.39(1)µB, extracted from low-temperature heat capacity and neutron diffraction measurements, is only 46% of the expected value of the static moment 3µB. This reduction indicates the presence of strong quantum fluctuations in the half-integer spin S=3/2 CaMnTeO6 magnet, which is rare. By comparing the spin-polarized band structure, chemical bonding, and physical properties of AMnTeO6 (A=Ca, Sr, Pb), how quantum-chemical interpretation can illuminate insights into the fundamentals of magnetic exchange interactions, providing a powerful tool for modulating spin dynamics with atomically precise control is demonstrated.

Effect of low-temperature neutron irradiation on the properties of titanium beryllide

Beryllium-based intermetallic compounds, such as Be12Ti, are increasingly being considered as a material capable of replacing pure beryllium in structural elements of fusion reactors. Be12Ti is considered as a neutron breeder material, a structural part of the Helium Cooled Pebble Bed of the DEMO reactor. It is expected that the replacement of beryllium by Be12Ti will make it possible to reduce the capture of tritium in the blanket without a significant decrease in the neutronic characteristics. Unlike beryllium, beryllides have relatively recently begun to be considered for use in nuclear and thermonuclear facilities, so the radiation resistance of these compounds remains little studied. This paper presents the experimental results on effect of low temperature neutron irradiation to properties of titanium beryllide samples manufactured by industrial technology in the Ulba Metallurgical Plant (UMP, Kazakhstan). The manufactured samples before and after irradiation were analyzed by scanning electron microscopy (SEM), X-Ray diffraction (XRD), hydrostatic weighing method, dimension method and microhardness measurement by Vickers method.

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.

Structure, Spin Correlations, and Magnetism of the S = 1/2 Square-Lattice Antiferromagnet Sr2CuTe1-xWxO6 (0 ≤ x ≤ 1).

Quantum spin liquids are highly entangled magnetic states with exotic properties. The S = 1/2 square-lattice Heisenberg model is one of the foundational models in frustrated magnetism with a predicted, but never observed, quantum spin liquid state. Isostructural double perovskites Sr2CuTeO6 and Sr2CuWO6 are physical realizations of this model but have distinctly different types of magnetic order and interactions due to a d10/d0 effect. Long-range magnetic order is suppressed in the solid solution Sr2CuTe1-xWxO6 in a wide region of x = 0.05-0.6, where the ground state has been proposed to be a disorder-induced spin liquid. Here, we present a comprehensive neutron scattering study of this system. We show using polarized neutron scattering that the spin liquid-like x = 0.2 and x = 0.5 samples have distinctly different local spin correlations, which suggests that they have different ground states. Low-temperature neutron diffraction measurements of the magnetically ordered W-rich samples reveal magnetic phase separation, which suggests that the previously ignored interlayer coupling between the square planes plays a role in the suppression of magnetic order at x ≈ 0.6. These results highlight the complex magnetism of Sr2CuTe1-xWxO6 and hint at a new quantum critical point between 0.2 < x < 0.4.

Unveiling the structural phase transition and magnetic structure of ternary boride PrIr3B2

We present a comprehensive study of PrIr3B2, which includes a detailed investigation of its crystal and magnetic structure using neutron diffraction. AC and DC magnetization and heat capacity data reveal antiferromagnetic ordering at T N = 10 K. The heat capacity measurements further exhibit a broad peak near 270 K which is related to a structural transition from P6/mmm to C2/m seen in low temperature x-ray diffraction and neutron diffraction. High intensity neutron diffraction data confirm the long-range ordering of Pr3+ spins, with no apparent magnetic moment on either of the Iridium sites. Two possible magnetic structures with either k 1 = [1,0,0] or k 2 = [½,½,0] fit nearly equally well the neutron diffraction data. However, based on previous magnetization studies on a single crystalline sample it is argued that the second solution with k 2 corresponds to the appropriate magnetic structure of PrIr3B2 below 10 K. In this magnetic structure, the Pr3+ moments are oriented at ∼45° to both the a and b axes, with the c-axis being the hard axis of magnetization. Overall, our results provide new insights into the magnetic and structural properties of PrIr3B2.

Fe Site Order and Magnetic Properties of Fe1/4NbS2.

Transition-metal dichalcogenides (TMDs) have long been attractive to researchers for their diverse properties and high degree of tunability. Most recently, interest in magnetically intercalated TMDs has resurged due to their potential applications in spintronic devices. While certain compositions featuring the absence of inversion symmetry such as Fe1/3NbS2 and Cr1/3NbS2 have garnered the most attention, the diverse compositional space afforded through the host matrix composition as well as intercalant identity and concentration is large and remains relatively underexplored. Here, we report the magnetic ground state of Fe1/4NbS2 that was determined from low-temperature neutron powder diffraction as an A-type antiferromagnet. Despite the presence of overall inversion symmetry, the pristine compound manifests spin polarization induced by the antiferromagnetic order at generic k points, based on density functional theory band-structure calculations. Furthermore, by combining synchrotron diffraction, pair distribution function, and magnetic susceptibility measurements, we find that the magnetic properties of Fe1/4NbS2 are sensitive to the Fe site order, which can be tuned via electrochemical lithiation and thermal history.

X-ray and Neutron Diffraction Studies of SrTe2FeO6Cl, an Oxide Chloride with Rare Anion Ordering.

The oxychloride SrTe2FeO6Cl is obtained by high-temperature solid-state synthesis under inert conditions in closed reaction vessels. The compound crystallizes in a novel monoclinic crystal structure that is described in the space group P121/n1 (No. 14). The unit cell parameters, a = 10.2604(1) Å, b = 5.34556(5) Å, c = 26.6851(3) Å, and β = 93.6853(4)°, and atomic parameters were determined from synchrotron diffraction data, starting from a model that was obtained from single-crystal X-ray diffraction data. The anion lattice exhibits a rare ordering of oxide and chloride ions: one-dimensional zig-zag ladders of chlorine (squarelike motif) are surrounded by an oxygen matrix. Two different iron sites coordinated solely to oxygen are present in the structure, one octahedral and one square pyramidal, both distorted. Similarly, two different strontium coordinations are present; the first homoleptic coordinated to eight oxygen atoms and the second heteroleptic coordinated to four oxygen and four chlorine atoms in a fac-like manner. The lone pair of Te(IV) is directed toward the larger chlorine atoms. Magnetic susceptibility measurements confirm that Fe is +3 (d5) in the high-spin electronic configuration, exhibiting an almost ideal spin-only moment, μeff = 5.65 μB Fe-1. The slightly negative Weiss constant (θCW = -39 K) suggests dominating antiparallel spin-to-spin coupling in the paramagnetic temperature range, agreeing with an observed long-range antiferromagnetic spin ordering below Néel temperature, TN ∼ 13 K, and a broad second order-like anomaly in the specific heat measurement data. Low-temperature neutron diffraction data reveal that the antiferromagnetic ordered phase is C-type, with a k-vector (1/2, 1/2, 0) and ordered moment of 4.14(7) μB. The spin structure can be described as antiferromagnetic ordered layers stacked along the a-axis, forming layers of squares that alternate along the c-axis.

Revisiting the magnetic structure of Holmium at high pressure by using neutron diffraction

Low-temperature neutron diffraction experiments at P= 8 GPa have been conducted to investigate the magnetic structures of metallic Holmium at high pressures by employing a long d-spacing high-flux diffractometer and a Paris-Edinburgh press cell inside a cryostat. We find that at P=8 GPa and T=5 K, no nuclear symmetry change is observed, keeping therefore the hexagonal closed packed (hcp) symmetry at high pressure. Our neutron diffraction data confirm that the ferromagnetic state does not exist. The magnetic structure corresponding to the helimagnetic order, which survives down to 5 K, is fully described by the magnetic superspace group formalism. These results are consistent with those previously published using magnetization experiments.

Evidence of Long-Range and Short-Range Magnetic Ordering in the Honeycomb Na3Mn2SbO6 Oxide

We present a comprehensive study of the synthesis, structure, and magnetic properties of the honeycomb oxide Na3Mn2SbO6 supported by neutron diffraction, heat capacity, and magnetization measurements. The refinements of the neutron diffraction patterns (150, 50, and 45 K) using the Rietveld method confirm the monoclinic (S. G. C2/m) structure. Temperature-dependent magnetic susceptibilities measured at varying fields along with the heat capacity measurements demonstrate the coexistence of long-range ordering (∼42 K) and short-range ordering (∼65 K). The field-dependent isothermal magnetization measurements at 5 K indicate a spin-flop transition around 5 T. Rietveld refinements of the low-temperature (below 45 K) neutron diffraction data further confirm the long-range magnetic ordering. In addition, the temperature variation of the lattice parameters obtained from the neutron powder diffraction analysis exhibited a distinct anomaly near the antiferromagnetic transition temperature. The appearance of the concomitant broadened backgrounds in the neutron powder diffraction data collected at 80, 50, and 45 K supports the short-range ordering. The resultant magnetic structure consists of spins that are aligned antiparallel with the nearest neighbors and also with the spins of the adjacent honeycomb layers. The occurrence of a fully ordered magnetic ground state (Neel antiferromagnetic (AFM)) in Na3Mn2SbO6 consolidates the significance of fabricating new honeycomb oxides.

Short-range magnetic correlation, metamagnetism, and coincident dielectric anomaly in Na5Co15.5Te6O36

Here we explore the structural, magnetic and dielectric properties of Co based compound Na$_5$Co$_{15.5}$Te$_6$O$_{36}$ as a candidate of short-range magnetic correlations driven development of dielectric anomaly above N$\acute{e}$el temperature of ($T_N$=) 50 K. Low temperature neutron powder diffraction (NPD) in zero applied magnetic field clearly indicates that the canted spin structure is responsible for the antiferromagnetic transition and partially occupied Co form short range magnetic correlation with other Co, which further facilitates the structural distortion and consequent development of dielectric anomaly above antiferromagnetic transition. Additionally, the temperature dependent magnetic heat capacity and electron spin resonance measurements reveal the presence of short-range magnetic correlations which coincides with an anomaly in the dielectric constant vs temperature curve. Moreover, significant changes in the lattice parameters are also observed around the same temperature, indicating presence of noticeable spin-lattice coupling. Further, sharp jump in the magnetic field dependent magnetization clearly indicates the presence of metamagnetic transition and magnetic field dependent NPD confirms that rotations of Co spins with applied magnetic field are responsible for this metamagnetic phase transition. As a result, this transition causes the magnetocaloric effect to be developed in the system, which is suitable for the application in low temperature refrigeration.

Spin canting and lattice symmetry in La2CuO4

While the dominant magnetic interaction in ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ is superexchange between nearest-neighbor Cu moments, the pinning of the spin direction depends on weak anisotropic effects associated with spin-orbit coupling. The symmetry of the octahedral tilt pattern allows an out-of-plane canting of the Cu spins, which is compensated by an opposite canting in nearest-neighbor layers. A strong magnetic field applied perpendicular to the planes can alter the spin canting pattern to induce a weak ferromagnetic phase. In light of recent evidence that the lattice symmetry is lower than originally assumed, we take another look at the nature of the field-induced spin-rotation transition. Comparing low-temperature neutron diffraction intensities for several magnetic Bragg peaks measured in fields of 0 and 14 T, we find that a better fit is provided by a model in which spins rotate within both neighboring planes but by different amounts, resulting in a noncollinear configuration. This model allows a more consistent relationship between lattice symmetry and spin orientation at all Cu sites.

Giant low-field magnetocaloric effect in ferromagnetically ordered Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds

Magnetocaloric material is the key working substance for magnetic refrigerant technology, for which the low-field and low-temperature magnetocaloric effect (MCE) performance is of great importance for practical applications at low temperatures. Here, a giant low-field magnetocaloric effect in ferromagnetically ordered Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds was reported, and the magnetic structure was characterized based on low-temperature neutron powder diffraction. With increasing Tm content from 0 to 1, the Curie temperature of Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds decreases from 16.0 K to 3.6 K. For Er0.7Tm0.3Al2 compound, it showed the largest low-field magnetic entropy change (–ΔSM) with the peak value of 17.2 and 25.7 J/(kg K) for 0–1 T and 0–2 T, respectively. The (–ΔSM)max up to 17.2 J/(kg K) of Er0.7Tm0.3Al2 compound for 0–1 T is the largest among the intermetallic magnetocaloric materials ever reported at temperatures below 20 K. The peak value of adiabatic temperature change (ΔTad)max was determined as 4.13 K and 6.87 K for 0–1 T and 0–2 T, respectively. The characteristic of second-order magnetic transitions was confirmed on basis of Arrott plots, the quantitative criterion of exponent n, rescaled universal curves, and the mean-field theory criterion. The outstanding low-field MCE performance with low working temperatures indicates that Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds are promising candidates for magnetic cooling materials at liquid hydrogen and liquid helium temperatures.

Effects of pre-stress on the mechanical properties and microstructure of neutron-irradiated high-purity aluminum

Although structural materials in nuclear reactors are usually serviced under pre-stressed conditions, the irradiated mechanical properties and microstructures for prestressed metals have not been well understood due to the experimental challenges. In this study, the annealed high-purity aluminum was subjected to a low temperature (313 K) neutron irradiation under a stress of 1.5 MPa, which was ten percent of its unirradiated yield strength. Post-irradiation tensile tests were carried out at 300 K with a strain rate of 1.1 × 10−3 s−1. A strong radiation-induced hardening as well as a loss of uniform ductility was observed on all the specimens, and the pre-stress could defer irradiation hardening and embrittlement and decrease plastic instability stress, which was involved with a possible asymmetry distribution of voids induced by the pre-stress. Transmission electron microscopy (TEM) was conducted on the samples to quantify the void size and density as a function of pre-stress and dose. It was shown that the pre-stress could accelerate the void nucleation, increase the density but decrease the size of voids. Although previous studies have reported that the dislocation channel could be probably attributed to the micro-mechanism for irradiation embrittlement, none of dislocation channels were discovered in the deformed irradiated high-purity aluminum samples, which implied that the dislocation channel is unnecessary for irradiation embrittlement. In addition, a neutron irradiation embrittlement model for metals, which had been built on the basis of Johnson-Cook constitutive model, was found applicable to metals irradiated with pre-stress. The stimulated results also well agreed with the experimental data.

Magnetic structure and properties of the vanthoffite mineral Na6Mn(SO4)4

A detailed analysis of the magnetic properties of a vanthoffite type mineral Na6Mn(SO4)4 basedon dc magnetization, low temperature neutron powder diffraction and theoretical calculations is reported. The mineral crystallizes in a monoclinic system with space group P21/c, where MnO6 octahedra are linked via SO4 tetrahedra. This gives rise to super-exchange interaction between two Mn2+ ions mediated by two nonmagnetic bridging anions and leads to an antiferromagnetic ordering below 3 K. The magnetic structure derived from neutron powder diffraction at 1.7 K depicts an antiferromagnetic spin arrangement in the bc plane of the crystal. The magnetic properties are modelled by numerical calculations using exact diagonalization technique, which fits the experimental results and provides antiferromagnetic ground state of Na6Mn(SO4)4.

Impact of Low-Temperature Neutron Irradiation on Tensile Behavior of Base Metal and Electron-Beam Welded 316L Stainless Steel

Impact of Low-Temperature Neutron Irradiation on Tensile Behavior of Base Metal and Electron-Beam Welded 316L Stainless Steel

RADIATION DAMAGE TO BERYLLIUM UNDER LOW-TEMPERATURE NEUTRON IRADIATION

In this work, to assess the radiation damage of beryllium under low-temperature neutron irradiation, samples from beryllium grade TShG-200 with an oxide phase concentration of about 1 wt % were studied, which were kept in the IVG.1M research reactor for a long time and were irradiated to fluences 0.8–4·1020 neut./cm2. Also, unirradiated original witness samples of the same brand were tested to compare the results.The aim was to establish the level of radiation degradation of beryllium samples during their tests in the IVG.1M reactor. Mechanical tests for three-point bending and tension were performed to determine the strength of beryllium samples, and their microhardness was also measured. To determine the degree of swelling of the beryllium samples their densities were measured by the method of hydrostatic weighing in the medium of distilled water.According to the results of short-term bending and tensile tests, it was found that the beryllium material after reactor irradiation softens in the range of 9.3–16.7%. And the results of measuring the microhardness showed an increase of up to 23%. Density results did not reveal swelling of the samples after low-temperature neutron irradiation.After mechanical tests, special studies of fractures and microstructural analysis were carried out, which did not reveal noticeable changes in the microstructure of beryllium after irradiation.

Magnetic structure of fluorophosphate Na2MnPO4F sodium battery material

The magnetic structure and properties of fluorophosphate Na2MnPO4F sodium insertion material, assuming a monoclinic (s.g. P21/n, #14) framework, were examined with the help of magnetic susceptibility and neutron powder diffraction. A long-range antiferromagnetic ordering was observed below the Néel temperature (TN) ∼10.4 ​K. Low temperature neutron powder diffractograms were refined to obtain the magnetic structure of fluorophosphate Na2MnPO4F. Below the TN, a commensurate antiferromagnetic spin structure was observed with a propagation vector k = (0, 0, 0), described by the magnetic space group P21/c' (#14.78). The magnetic order is presumably driven by the superexchange interactions via corner-shared F atoms of the octahedral Mn2O8F2 chains running along b-axis.

High cubicity of D2O ice inside spherical nanopores of MIL-101(Cr) framework: a neutron diffraction study.

Although cubic ice (ice Ic) is considered to be an important phase of water that impacts ice cloud formation in the Earth's upper atmosphere, its properties have not been studied to the same extent as those of hexagonal ice (ice Ih). This is because pristine ice Ic is not formed in simple laboratory conditions. Ice Ic formed in ambient conditions has a stacking disordered array of both hexagonal and cubic-structured hydrogen-bonded water molecules. It is therefore an active area of research to find ways of developing stacking disorder-free pure ice Ic. We demonstrate the evolution of almost pure ice Ic structure within the spherical nanopores of a hydrostable Cr-based metal-organic framework MIL-101(Cr) with an average pore size of 1 nm by low-temperature neutron diffraction study on D2O. It is observed that at temperatures below 230 K a fraction of liquid D2O transforms into ice and more than 94% of ice crystals evolved inside the pore are cubic in shape. This is a significantly high fraction of ice Ic formed under simple conditions inside the spherical pores of a Cr-based MOF. It is also observed that upon increasing the temperature, ice Ic remains stable until its melting point, without being transformed into ice Ih. This observation is in contrast to our previous observation of ice structure in the 2D cylindrical nanopores of MCM-41, where H2O ice after creeping out from the cylindrical channel was seen to be dominated by hexagonal shape. In the present study, the D2O molecules were confined into well-defined spherical nanopores, which hindered the growth of crystals above a certain size, thus minimizing the stacking disordered array. Nanoconfinement of water inside uniform spherical pores is therefore a promising method for the evolution of a significantly large fraction of cubic ice by minimizing the stacking disorder. This finding may open up the possibility of forming ice Ic with 100% cubicity under simple laboratory conditions, which will help in exploring the microphysics of ice cloud formation in the upper atmosphere.

Non-ambient X-ray and neutron diffraction of novel relaxor ferroelectric xBi2(Zn2/3,Nb1/3)O3-(1 - x)BaTiO3.

The first determination of the phase diagram of the novel ferroelectric relaxor xBi(Zn2/3Nb1/3)O3-(1 - x)BaTiO3 (BZN-BT) has been achieved with a combination of high-resolution X-ray and neutron diffraction up to the miscibility limit near x(BZN) = 20.0% over a temperature range 20 < T < 400 K. The combined X-ray and neutron data show that the instability within the xBZN-(1-x)BT system reaches a maximum at x = 3.9% and is driven by B-site displacement and distortion of the oxygen octahedra in the polar phases. Composition-dependent effects include a narrow Amm2-dominated region focused at x = 3.9%, significant convergence of the lattice parameters in both P4mm and Amm2 phases, and sharp maxima in piezoelectric coefficient d 33 and maximum polarization P max. Lattice parameter dilation at x ≥ 4.0% was observed for both P4mm and Amm2 unit cells, alongside the first appearance of Pm 3 m at 295 K and the onset of significant dielectric relaxation. Low-temperature neutron diffraction indicated a weak or non-existent temperature dependence on the transition from ferroelectric at x = 3.9% to ferroelectric relaxor at x = 4.0%. Temperature-dependent phase transitions were eliminated near x = 3.0%, with the ferroelectric limit observed at x = 5.0% and a transition to a low-loss relaxor dielectric near x = 8.0%.