Topologically nontrivial spin textures host great promise for future spintronic applications. Skyrmions in particular are of burgeoning interest owing to their nanometric size, topological protection, and high mobility via ultra-low current densities. It has been previously reported through magnetic susceptibility, microscopy, and scattering techniques that Co${}_8$Zn${}_8$Mn${}_4$ forms an above room temperature triangular skyrmion lattice. Here, we report the synthesis procedure and characterization of a polycrystalline Co${}_8$Zn${}_8$Mn${}_4$ disordered bulk sample. We employ powder X-ray diffraction and backscatter Laue diffraction as characterization tools of the crystallinity of the samples, while magnetic susceptibility and Small Angle Neutron Scattering (SANS) measurements are performed to study the skyrmion phase. Magnetic susceptibility measurements show a dip anomaly in the magnetization curves, which persists over a range of approximately 305 K–315 K. SANS measurements reveal a rotationally disordered polydomain skyrmion lattice. Applying a symmetry-breaking magnetic field sequence, we were able to orient and order the previously jammed state to yield the prototypical hexagonal diffraction patterns with secondary diffraction rings. This emergence of the skyrmion order serves as a unique demonstration of the fundamental interplay of structural disorder and anisotropy in stabilizing the thermal equilibrium phase.

If the wavelength of radiation and the size of inhomogeneities in the medium are approximately equal, the radiation might be intensively scattered in the medium and reflected from its surface. Such efficient nanomaterial reflectors are of great scientific and technological interest. In previous works, we demonstrated a significant improvement in the efficiency of reflection of slow neutrons from a powder of diamond nanoparticles by replacing hydrogen located on the surface of nanoparticles with fluorine and removing the residual sp² amorphous shells of nanoparticles via the fluorination process. In this paper, we study the mechanism of this improvement using a set of complementary experimental techniques. To analyze the data on a small-angle scattering of neutrons and X-rays in powders of diamond nanoparticles, we have developed a model of discrete-size diamond nanospheres. Our results show that fluorination does not destroy either the crystalline cores of nanoparticles or their clustering in the scale range of 0.6–200 nm. This observation implies that it does not significantly affect the neutron scattering properties of the powder. We conclude that the overall increase in reflectivity from the fluorinated nanodiamond powder is primarily due to the large reduction of neutron losses in the powder caused by the removal of hydrogen contaminations.

Neutrons can be an instrument or an object in many fields of research. Major efforts all over the world are devoted to improving the intensity of neutron sources and the efficiency of neutron delivery for experimental installations. In this context, neutron reflectors play a key role because they allow significant improvement of both economy and efficiency. For slow neutrons, Detonation NanoDiamond (DND) powders provide exceptionally good reflecting performance due to the combination of enhanced coherent scattering and low neutron absorption. The enhancement is at maximum when the nanoparticle diameter is close to the neutron wavelength. Therefore, the mean nanoparticle diameter and the diameter distribution are important. In addition, DNDs show clustering, which increases their effective diameters. Here, we report on how breaking agglomerates affects clustering of DNDs and the overall reflector performance. We characterize DNDs using small-angle neutron scattering, X-ray diffraction, scanning and transmission electron microscopy, neutron activation analysis, dynamical light scattering, infra-red light spectroscopy, and others. Based on the results of these tests, we discuss the calculated size distribution of DNDs, the absolute cross-section of neutron scattering, the neutron albedo, and the neutron intensity gain for neutron traps with DND walls.

Over a decade ago, it was confirmed that detonation nanodiamond (DND) powders reflect very cold neutrons (VCNs) diffusively at any incidence angle and that they reflect cold neutrons quasi-specularly at small incidence angles. In the present publication, we report the results of a study on the effect of particle sizes on the overall efficiency of neutron reflectors made of DNDs. To perform this study, we separated, by centrifugation, the fraction of finer DND nanoparticles (which are referred to as S-DNDs here) from a broad initial size distribution and experimentally and theoretically compared the performance of such a neutron reflector with that from deagglomerated fluorinated DNDs (DF-DNDs). Typical commercially available DNDs with the size of ~4.3 nm are close to the optimum for VCNs with a typical velocity of ~50 m/s, while smaller and larger DNDs are more efficient for faster and slower VCN velocities, respectively. Simulations show that, for a realistic reflector geometry, the replacement of DF-DNDs (a reflector with the best achieved performance) by S-DNDs (with smaller size DNDs) increases the neutron albedo in the velocity range above ~60 m/s. This increase in the albedo results in an increase in the density of faster VCNs in such a reflector cavity of up to ~25% as well as an increase in the upper boundary of the velocities of efficient VCN reflection.

Nanomaterials can intensively scatter and/or reflect radiation. Such processes and materials are of theoretical and practical interest. Here, we study the quasi-specular reflections (QSRs) of cold neutrons (CNs) and the reflections of very cold neutrons (VCNs) from nanodiamond (ND) powders. The fluorination of ND increased its efficiency by removing/replacing hydrogen, which is otherwise the dominant cause of neutron loss due to incoherent scattering. The probability of the diffuse reflection of VCNs increased for certain neutron wavelengths by using appropriate ND sizes. Based on model concepts of the interaction of CNs with ND, and in reference to our previous work, we assume that the angular distribution of quasi-specularly reflected CNs is narrower, and that the probability of QSRs of longer wavelength neutrons increases if we increase the characteristic sizes of NDs compared to standard detonation nanodiamonds (DNDs). However, the probability of QSRs of CNs with wavelengths below the cutoff of ~4.12 Å decreases due to diffraction scattering on the ND crystal lattice. We experimentally compared the QSRs of CNs from ~4.3 nm and ~15.0 nm ND. Our qualitative conclusions and numerical estimates can help optimize the parameters of ND for specific practical applications based on the QSRs of CNs.

Electroless nickel plating of various alloys is one of the most technologically mature methods for producing functional coatings with high corrosion resistance, wear resistance, and stable service performance. In the field of ultracold neutron (UCN) physics, nickel-phosphorus coatings based on the ⁵⁸Ni isotope are of particular interest. Its exceptionally high neutron optical potential, approximately 342 neV, is substantially higher than that of natural nickel, which is approximately 245.5 neV. At the same time, ⁵⁸Ni and natural nickel have essentially identical chemical properties and differ only in their nuclear characteristics; therefore, process development and optimization of the deposition procedure can be performed using the more readily available natural nickel. The incorporation of phosphorus decreases the total neutron optical potential to values in the range of 190–220 neV, but makes it possible to modify the magnetic properties of the nickel coating in order to reduce magnetic losses of UCN upon reflection from the surface. Although extensive studies have been devoted to the deposition of Ni-P coatings on aluminum and steel substrates, the formation of high-quality coatings on beryllium- and zirconium-based alloys remains insufficiently investigated. These materials are of particular interest for chambers of superfluid-helium-based UCN sources, since they can reduce activation-related heat loads and ensure efficient cooling of the source to the required temperatures of approximately 1 K under high-radiation-flux conditions. In this work, electroless Ni–P coatings deposited on the surfaces of the aluminum–magnesium alloy AMg6, the aluminum–beryllium alloy AM162H, and the zirconium alloy Zircaloy-4 were systematically investigated, with particular emphasis on AM162H and Zircaloy-4 as promising structural materials for UCN-source chambers. The deposited coatings were comprehensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma optical emission spectrometry (ICP-OES), surface profilometry, instrumented nanoindentation, scratch testing, and electrochemical polarization measurements followed by Tafel analysis. These complementary techniques provided information on the phase-structural state, surface morphology, continuity, thickness, elemental composition, roughness, hardness, elastic modulus, indentation stiffness, adhesion behavior, and corrosion resistance of the coatings. The ICP-OES measurements independently confirmed the compositional trend established by EDS. The coatings deposited on AM162H and Zircaloy-4 exhibited higher hardness and substantially better corrosion resistance than Ni–P/AMg6. Scratch testing indicated satisfactory interfacial adhesion for the coatings on AMg6 and AM162H, whereas the Ni–P/Zircaloy-4 coating exhibited comparatively weaker adhesion to the substrate under the applied test conditions. Particular attention was paid to coating continuity, composition, and thickness because through-thickness defects would expose the substrate, which has a lower neutron optical potential, impurity elements could increase UCN absorption and reduce the neutron optical potential of the coating, and an appropriately selected coating thickness would enable the rational use of the expensive ⁵⁸Ni isotope. The results provide an experimental basis for further optimization of electroless Ni–P coatings for components of UCN production and storage systems.