In contrast to conventional neutron imaging by measuring the attenuation contrast, polarized-neutron imaging (PNI) has proved to be a powerful tool for investigating the spatial distribution of magnetic fields inside and around bulk samples owing to the intrinsic magnetic moment of neutrons. This technique benefits from the measurement of the cumulative precession of the neutron polarization passing through a magnetic field. We report the recent development of the PNI capability at the China Advanced Research Reactor (CARR), where two neutron imaging instruments (thermal and cold) have been established. To further develop and realize the PNI technique, a PNI facility consisting of a double-crystal pyrolytic graphite monochromator, supermirror polarizer with three parallel V-shaped cavities and an in situ optically pumped ^3 He neutron spin filter as a neutron spin analyzer was successfully developed and tested based on an established cold neutron imaging instrument. This setup will be beneficial for enhancing neutron imaging and neutron optics in CARR in the future.

We report the identification and characterization of a new compound Fe0.68Pd0.80Te with an α-Fe1+xTe prototype structure. Different from the Fe-square net and minor occupancy of interstitial Fe-sites in Fe1+xTe, Fe0.68Pd0.80Te is featured by a Pd-square net and near 68% occupancy of the corresponding interstitial Fe-sites. Furthermore, noncontact atomic force microscopy and X-ray diffraction provide evidence for the existence of a 3 × 3 × 3 Pd-vacancy order in this layered material. A spin-glass ground state below Tg ∼40 K is identified via magnetic characterization. Electrical transport measurements show that Fe0.68Pd0.80Te is a semiconductor with a very small band gap below 10 meV. It has weak negative magnetoresistance and hole-like charge carriers below room temperature. Our results demonstrate its potentials for further exploring various quantum phenomena.

In a magnetic skyrmion phase, magnetic moments form vortex-like topological textures which are of both fundamental and industrial interests. In $\beta$-Mn-type Co-Zn-Mn alloys, chrial magnetic skyrmions emerge above room temperature, providing a unique system for studying the skrymion physics and exploring spintronics applications. However, the magnetic skyrmion phase is typically confined in a narrow and limited temperature ($T$) and magnetic field ($H$) range. Here, we demonstrate that hydrostatic pressure can expand the skyrmion phase in the $T-H$ phase diagram of single-crystalline Co$_8$Zn$_8$Mn$_4$. At ambient pressure, signatures of skyrmions are seen within $T\sim302-308$ K and $H\sim50-100$ Oe. Applying a moderate pressure of 6 kbar extends this range to $T\sim300-310$ K and $H\sim50-150$ Oe. However, further escalation of pressure to 10 kbar results in a slight contraction of the skyrmion phase. These findings underscore the sensitivity of the skyrmion phase in Co$_8$Zn$_8$Mn$_4$ to external pressures, and hint at the potential of strain engineering, particularly in $\beta$-Mn-type Co-Zn-Mn thin films, as a promising avenue to customize the skyrmion phase.

Fabricating electromagnetic coupling carbon-based aerogels with tightly bound and uniformly distributed components is a proven strategy for improving electromagnetic wave absorption (EWA) performance. Herein, highly ordered porous cobalt/cobalt (II) oxide/carbon (Co/CoO/C) aerogels were successfully fabricated via ice-templated freeze casting coupled with one-step carbonization, relying on the complexation reaction between cobalt ions and chitosan. The optimal sample, Co/CoO/C-1.0, achieves a minimum reflection loss (RLmᵢn) of −58.15 dB and an effective absorption bandwidth (EAB) of 6.48 GHz at a thickness of 2.2 mm. Additionally, the aerogel exhibits excellent radar stealth performance (with a significant reduction in radar cross-section, RCS) and thermal insulation properties. Gradient structural design effectively extends the effective absorption bandwidth (EAB) to 11.23 GHz. Mechanism analysis reveals that the outstanding EWA performance of these aerogels stems from the synergistic effect of diverse attenuation pathways, including multiple scattering, dipole polarization, interfacial polarization, conduction loss and magnetic resonance. The regulation of cobalt content effectively achieves an optimal balance between impedance matching and electromagnetic loss. This multifunctional Co/CoO/C aerogel integrating EWA, radar stealth and thermal insulation capabilities possess great application prospects under complex service conditions and provide critical guidance for the rational design of carbon-based EWA absorbers.

CrRhAs was theoretically proposed to be a kagome metal with unusual magnetic ground states; however, little is known about its magnetic structure and physical properties experimentally. Here, we present an experimental investigation of CrRhAs with ZrNiAl-type structure and a distorted Cr kagome lattice. CrRhAs is an antiferromagnet with TN = 149 K. Powder neutron diffraction analysis reveals a noncollinear antiferromagnetic structure with propagation vector k = (1/3, 1/3, 1/2), which features a ferromagnetic second nearest neighbor coupling in the kagome plane that is different from the prediction in previous density functional theory calculations. Furthermore, CrRhAs exhibits anomalous electrical transport properties which are possibly related to multiband effects and strong spin fluctuations. For the temperature-dependent longitudinal resistivity rho xx, it is semiconductinglike above TN and becomes metallic below TN. The Hall coefficients exhibit two sign changes near 70 and 300 K. Combined with the results of heat capacity measurements, a large Kadowaki-Woods ratio alpha = 33.9 & micro;S2 cm mol2 K2/J2 is obtained. The above results suggest CrRhAs is a strongly correlated kagome metal with multiband and noncollinear magnetic structure features.

Phonons, as the primary heat carriers, play an important role in the thermal management of AlN-based semiconductor devices. Acoustic phonon dispersion curves of a large single crystal of hexagonal AlN have been measured by inelastic neutron scattering experiments along different high symmetry directions. The corresponding longitudinal and transverse sound velocities and the associated elastic constants have been deduced. The results show good agreement with first principles calculations as well as the previous experimental data. The influence of pressure on the the lattice dynamics and mechanical properties has also been predicted.

Neutron scattering is a powerful technique for investigating crystal structure, magnetic structure and microscopic dynamical properties by analyzing the energy and momentum transfers between incident neutrons and the sample. This paper presents the key design specifications and technical parameters of two advanced neutron inelastic scattering instruments, developed over six years: XINGZHI cold neutron triple-axis spectrometer with polarization analysis, and BOYA multiplexing cold neutron spectrometer.u201D For u201CXINGZHI,u201D the implementation and test results of the S-bender supermirror neutron polarizer are presented, which marks the first use of S-benders both before and after the sample position on a triple-axis spectrometer for polarized neutron experiments. Meanwhile, u201CBOYAu201D features an innovative crystal double-column Rowland focusing analyzer design that optimizes energy resolution and enhances signal intensity. This spectrometer can simultaneously map excitation spectra across 34 momentum transfers within a 119u00B0 scattering angle range. Each analyzer channel includes five fixed final energy levels, plus an elastic diffraction channel, achieving a detection efficiency two orders of magnitude higher than that of conventional triple-axis spectrometers. Finally, experimental studies and data analyses conducted using u201CXINGZHIu201D and u201CBOYAu201D will investigate applications in condensed matter physics, focusing on topics such as unconventional superconductors, quantum spin liquid candidates, multiferroic materials, and low-dimensional magnetic systems.

CoSb3-based skutterudites have emerged as promising candidates for midtemperature thermoelectric (TE) applications. However, their further performance enhancement is hindered by intrinsically high lattice thermal conductivity and strong intercoupling among TE transport parameters. In this work, we introduce low-melting-point Sb2O3 as an oxidizing agent into the classical Yb0.3Co4Sb12 system via a melt-spinning technique to optimize its TE transport properties. In situ oxidation generates high-melting-point Yb2O3 nanoprecipitates within the matrix while simultaneously reducing the Yb filling fraction. To address this, we employ a stoichiometric compensation strategy by incorporating additional Yb:Sb2O3 in a 2:1 ratio, thereby achieving controlled Yb2O3 nanoparticle precipitation while maintaining optimal Yb filling. The engineered oxide nanophase exhibits dual functionality: (1) carrier energy filtering enhances the power factor to 61 μW cm-1 K-2, and (2) multiscale phonon scattering suppresses the lattice thermal conductivity to 0.4 W m-1 K-1. These synergistic effects yield a record-high peak ZT of 1.58 at 873 K (a 32% enhancement) and an exceptional average ZT of 1.05 across 300-873 K in the Yb0.36Co4Sb12/0.03 Sb2O3 composite. This work established a paradigm for decoupling electronic and phonon transport through nanophase precision oxide nanophase engineering.

A methodology of reconstructing the known and homogeneous magnetic field for an aluminum wire solenoid coil was demonstrated. The magnetic field distributions inside the solenoid coil at different applied currents and solenoid orientations were successfully measured using polarized neutron imaging technique. Finite element method, combined with Monte Carlo simulation, were employed to calculate the magnetic field distributions inside the solenoid coil. The obtained results show that combining finite element and Monte Carlo methods greatly promote the development of polarized neutron imaging technique.

Rare-earth permanent magnet (PM) materials have challenges in production and application due to resource distribution, cost, environmental unfriendliness, and recycling difficulties. Thus, the demand for high-performance rare-earth-free PM has increased...

Metallic Magnetic Calorimeters (MMC) are low-temperature particle detectors based on calorimetry, typically operating at ultra-low temperatures below 100 mK, and they utilize metallic paramagnetic temperature sensors to convert the temperature rise of the absorber upon absorption of high-energy particles into changes in magnetic flux detected by a superconducting quantum interference device (SQUID). Therefore, the design of the MMC heat coupling system is directly related to the signal characteristics and performance of the MMC, making it particularly important for the design of MMC heat coupling systems. This paper, based on the basic principles of MMC signal conversion and the thermal coupling characteristics of components, combines actual conditions and uses the COMSOL heat conduction module to simulate the MMC heat coupling system. Key components of the MMC heat coupling system, including the absorber, thermal bottleneck, paramagnetic sensor, and weak thermal link, have been optimized in terms of parameter design. The optimized design is proposed based on simulation results and practical considerations. Simulation results show that for the detection of the characteristic 5.9 key gamma rays from 55Fe, when the MMC absorber thickness is reduced to 6 mu m and the paramagnetic sensor thickness is reduced to 1.5 mu m, the signal amplitude of the CMG-I can be increased by more than 100 % at a working temperature of 30 mK without affecting the MMC signal response and ensuring almost 100 % stopping power; by adding four gold posts between the absorber and the paramagnetic sensor as thermal bottlenecks, with a total cross-sectional area of 5.58 % of the absorber area, the process difficulty can be significantly reduced while ensuring complete thermalization of the incident energy within the absorber and essentially eliminating position dependence; the introduction of gold thermalization strip can provide a fully metallic thermal link from the absorber-paramagnetic sensor system to the rear thermal bath, reducing the relaxation time to approximately 4.844 ms, about one-third of the original design, which can significantly increase the count rate without significantly affecting the MMC signal amplitude and reduce the negative impact on energy resolution caused by signal pile-up. The research results have a significant guide for the design of MMC heat coupling systems.

It has been established that both hybridization with magnetic rare earth cation and crystal field originating from structural anisotropy can affect the spin orientation of magnetic transition metal perovskite. In this work, we have systematically studied the crystal structure, magnetization, and magnetic structure of Mn-doped rare earth orthochromites HoCr1_xMnxO3 (x = 0-0.85) by means of X-ray diffraction, magnetometry, and neutron powder diffraction. With increasing Jahn-Teller active Mn3+-substitution for Cr3+, the crystallographic distortion is gradually enhanced and causes a systematic evolution of magnetism. With doping, the Cr(Mn) ordering temperature is gradually suppressed, and multiple magnetic configurations Gamma 2, Gamma 1, and Gamma 4 phases appear consecutively. The rich transition phenomena are ascribed to a competition between increased structural anisotropy and weakened Ho-Cr(Mn) hybridization with doping. In a low doping regime with x = 0.1-0.5, Gamma 2 phase is pre-dominant in low temperature, and a magnetization reversal is observed, reflecting the opposite sign of Cr-Mn DMI coefficient with respect to the Cr-Cr and Mn-Mn interaction. In the high doping range with x = 0.6-0.8, the long-range order of Cr(Mn) sublattice is gradually suppressed while a short-range order becomes dominant. For x = 0.85, a magnetic structure resembling o-HoMnO3 is observed.

Metallic magnetic calorimeters are a class of low-temperature particle detectors based on calorimetry, utilizing metallic paramagnetic temperature sensors to convert the temperature rise of an absorber upon the absorption of incident particle energy into a change in magnetic flux, which detected by a superconducting quantum interference device (SQUID). This process enables high-resolution measurements of radiation with exceptional precision. However, metallic magnetic calorimeter signals are inherently weak and highly susceptible to noise, making the extraction of pulse amplitude a significant challenge. Digital signal processing (DSP) plays a crucial role in the data processing of metallic magnetic calorimeter by employing digital filtering techniques to shape the signals and enhance energy resolution. This paper introduces a data acquisition system for metallic magnetic calorimeter based on a field-programmable gate array (FPGA), designed for high-speed signal acquisition, real-time control, signal processing, and display of spectra through an upper computer. Testing of the system yielded successful acquisition of both Co-60 spectra data and noise spectrum of metallic magnetic calorimeter. The linear correlation coefficient of R2 reached 0.9781, demonstrates the system’s effective signal acquisition capability. In offline mode, the shaping effects and energy resolution enhancement of traditional nuclear detector signals, simulated, and actual metallic magnetic calorimeter signals were compared using three filtering methods: trapezoidal, cusp, and gaussian filtering. The cusp filter proved to be the most effective, significantly improving the energy resolution of high-purity germanium spectra from 0.598 keV to 0.536 keV. This enhancement validates the correctness of digital signal processing and provides a reliable basis for the selection of digital filtering methods for metallic magnetic calorimeter. In summary, our research presents a comprehensive approach to metallic magnetic calorimeter signal acquisition and processing, highlighting the potential of digital signal processing to overcome the problem of the extraction of weak signals submerged in strong noise. The FPGA-based data acquisition system developed in this study offers an efficient solution for high-resolution radiation measurements.

Two-dimensional van der Waals single crystals DyOBr and SmOCl have been grown by a flux method, and their anisotropic magnetic properties are reported. DyOBr orders antiferromagnetically at TN = 9.5 K with magnetic moments lying along a axis, similar as DyOCl. Its magnetic susceptibility shows an anomaly at T* = 30 K, possibly due to the crystal field effect. Furthermore, a 1/3 magnetization plateau is clearly observed under H II a and H II [110], which might be a field-induced spin-flop phase or some exotic quantum magnetic state. On the other hand, isostructural SmOCl undergoes an antiferromagnetic transition at TN = 7.1 K and exhibits a contrasting Ising-like perpendicular c-axis magnetic anisotropy, which could be well explained by our crystal field calculations. Both DyOBr and SmOCl are insulators with a band gap of -5 eV, and our results suggest they are promising in building van der Waals heterostructures and applications in multifunctional devices.

The charge density wave (CDW) or nematicity has been found to coexist with superconductivity in many systems. Thus, it is interesting that the superconducting transition temperature T-c in the doped BaNi2As2 system can be enhanced up to six times as the CDW or nematicity in the undoped compound is suppressed. Here we show that the transverse acoustic phonons of Ba1-xSrxNi2As2 are strongly damped in a wide doping range and over the whole Q range, which excludes its origin from either CDW or nematicity. The damping of TA phonons can be understood as large electron-phonon coupling and possible strong hybridization between acoustic and optical phonons as shown by the first-principle calculations. The superconductivity can be quantitatively reproduced by the change of the electron-phonon coupling constant calculated by the McMillan equation in the BCS framework, which suggests that no quantum fluctuations of any order is needed to promote the superconductivity. On the contrary, the change of T-c in this system should be understood as the sixfold suppression of superconductivity in undoped compounds.

Two-dimensional (2D) magnets have attracted significant attentions in recent years due to their importance in the research on both fundamental physics and spintronic applications. Here, we report the discovery of a new ternary compound FePd2Te2. It features a layered quasi-2D crystal structure with one-dimensional Fe zigzag chains extending along the b-axis in the cleavage plane. Single crystals of FePd2Te2 with centimeter-size could be grown. Density functional theory calculations, mechanical exfoliation and atomic force microscopy on these crystals reveal that they are 2D materialsthat can be thinned down to 5 nm. Magnetic characterization shows that FePd2Te2 is an easy-plane ferromagnet with Tc 183 K and strong in-plane uniaxial magnetic anisotropy. Magnetoresistance and anomalous Hall effect demonstrate that ferromagnetism could maintain in FePd2Te2 flakes with large coercivity. A crystal twinning effect is observed by scanning tunneling microscopy which makes the Fe chains right-angle bent in the cleavage plane and creates an intriguing spin texture. Our results show that FePd2Te2 is a correlated anisotropic 2D magnets that may attract multidisciplinary research interests.

An innovative monochromator shielding is designed and implemented for the cold neutron spectrometers XINGZHI and BOYA operated by Renmin University of China at China Advanced Research Reactor. Via Monte Carlo simulations and careful mechanical designs, a shielding configuration has been successfully developed to satisfy safety requirements of below 3 μSv/h dose rate at its exterior, meanwhile fulfilling space, floor load and nonmagnetic requirements. Composite materials are utilized to form the sandwich-type shielding walls: the inner layer of boron carbide rubber, the middle layer of steel-encased lead and the outer layer of borated polyethylene. Special-shaped liftable shielding blocks are incorporated to facilitate a continuous adjustment of the neutron energy while preventing radiation leakage. Our work has demonstrated that by utilizing composite shielding materials, along with the sandwich structure and liftable shielding blocks, a compact and lightweight shielding solution can be achieved. This enables the realization of advanced neutron scattering instruments that provide expanded space of measurement, larger energy and momentum coverage, and higher flux on the sample. This shielding represents the first of its kind in neutron scattering instruments in China. Following its successful operation, it has been subsequently employed by other neutron instruments across the country.

Metallic magnetic calorimeters (MMC) are low-temperature particle detectors based on calorimetry. They typically operate at temperatures below 100 mK. They utilize a metallic paramagnetic temperature sensor to convert the temperature rise of an absorber, during the absorption of energetic particles, into a change in magnetic flux sensed by a superconducting quantum interference device (SQUID). Since the SQUID has a high sensitivity to magnetic signals, the MMC system is very sensitive to external magnetic field interference. The magnetic shielding effect of the MMC directly affects its detection capability. Therefore, the design of the MMC magnetic shield system is particularly important. In this study, a set of MMC magnetic shields is designed based on the principle of magnetic shielding. The design is optimized using the COMSOL magnetic field simulation module by varying relevant parameters, such as the thickness and height of the shields as well as the diameter of the radioactive source hole, which determines the magnetic shielding effect. Through the simulation, the optimized magnetic shielding device can reduce the magnetic field interference of 2–0.0264 nT. The value can be further reduced by one order of magnitude if a high-permeability material with superior performance is used. This research is instructive for the design of MMC magnetic shielding devices in subsequent experiments.

Halide perovskites emerge as promising candidates for thermoelectrics due to their ultralow thermal conductivity. The conventional theory based on the phonon gas model, which treats thermal transport as particle-like behavior, shows limitations to describe the unusual thermal transport property in some halide perovskites with strong anharmonicity. Here, the significance of phonon coherence effect on thermal transport of bismuth-halide perovskite Cs3Bi2Br9 is reported by inelastic neutron scattering and simulations including density functional theory and machine-learning potential based molecular dynamics. This study shows that the restrictive low-energy acoustic phonons lead to the limited particle-like thermal conductivity, which seriously underestimates the lattice thermal conductivity of Cs3Bi2Br9. The significant contribution of wave-like optical phonon modes, driven by the coherence effect, accounts for an additional approximate to 50% wave-like thermal conductivity. Besides, the experimental weak temperature dependence of thermal conductivity along z direction (kappa( )approximate to T-0.35) is well reproduced by calculation (kappa( )approximate to T-0.37) when including phonon coherence. This work highlights the critical role of phonon coherence in Cs3Bi2Br9 and enhances understanding on the unusual thermal transport properties in halide perovskites and other related materials with strong anharmonicity.