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Engineering of materials with specific physical properties has recently focused on the effect of nano-sized ‘guest domains’ in a ‘host matrix’ that enable tuning of electrical, mechanical, photo-optical or thermal properties. A low thermal conductivity is a prerequisite for obtaining effective thermoelectric materials, and the challenge is to limit the conduction of heat by phonons, without simultaneously reducing the charge transport. This is named the ‘phonon glass–electron crystal’ concept and may be realized in host–guest systems. The guest entities are believed to have independent oscillations, so-called rattler modes, which scatter the acoustic phonons and reduce the thermal conductivity. We have investigated the phonon dispersion relation in the phonon glass–electron crystal material Ba 8 Ga 16 Ge 30 using neutron triple-axis spectroscopy. The results disclose unambiguously the theoretically predicted avoided crossing of the rattler modes and the acoustic-phonon branches. The observed phonon lifetimes are longer than expected, and a new explanation for the low κ L is provided. The presence of guest atoms—known as rattlers—in the cages of some clathrate structures is considered to be responsible for the low thermal conductivity of the materials. Neutron spectroscopy provides important evidence regarding the actual phonon dispersion in the material, and the precise way in which this is influenced by rattlers.

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin–orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear ( C 4 ) to pseudo-linear ( D 4d ) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting. Suppression of quantum tunneling in molecular magnets is key for their magnetic behaviours to be exploitable. Here, the authors show that tuning the geometry of lanthanide single-ion magnets leads to a suppression of the quantum tunneling, finding a three-fold reduction of the tunnel splitting upon changing the crystal field symmetry.

When charged particles in periodic lattices are subjected to a constant electric field, they respond by oscillating. Here we demonstrate that the magnetic analogue of these Bloch oscillations are realised in a ferromagnetic easy axis chain. In this case, the “particles” undergoing oscillatory motion in the presence of a magnetic field are domain walls. Inelastic neutron scattering reveals three distinct components of the low energy spin-dynamics including a signature Bloch oscillation mode. Using parameter-free theoretical calculations, we are able to account for all features in the excitation spectrum, thus providing detailed insights into the complex dynamics in spin-anisotropic chains. An electron subject to a periodic potential and a constant electric field exhibit oscillatory dynamics, known as Bloch oscillations. Here, the authors demonstrate a magnetic analogue of Bloch oscillations in a ferromagnetic near-Ising chain, where magnetic excitations oscillate in response to a magnetic field.

Monochromator and analyzer systems that rely on bent single crystals are in use throughout the neutron scattering community. An adequate component for the simulation of such crystals was missing in the widely used neutron simulation software package McStas. The newly developed component Monochromator_bent, which fills this gap, is introduced. It can serve as a model for crystal monochromators and analyzers of various kinds, including the bent perfect crystals, mosaic crystals, and crystals combining mosaicity with bending. The performance of the component is tested at several configurations and compared with the results of another simulation program, SIMRES. Validation is carried out using analytical calculations and the McStas NCrystal_sample component for the case of unbent crystals. Excellent agreement in all tests and good performance in terms of computing speed has been found. The component has been included in the present distribution of McStas 3.5.

Neutrons, owing to their unique properties, serve as indispensable probes for investigating the structure and dynamics of materials across various length scales. The scientific community utilizing neutron research infrastructures encompasses a diverse range of disciplines, making it challenging to quantify its scientific and societal impact. To address this challenge, we apply Natural Language Processing (NLP) and machine learning techniques to analyze the scientific output of the European neutron science community. Leveraging open-source software toolkits, our method allows for the quantitative assessment of community evolution and research focus. Our analysis reveals consistent growth in the neutron community despite a reduction in sources, underscoring the enduring significance of neutron methods in scientific research. Furthermore, an increase in unique authors and an even distribution of publications across diverse scientific topics highlight the community’s interdisciplinary nature and collaborative spirit. While this study emphasizes neutron scattering, our methodology holds promise for a broad range of scientific communities reliant on Large Research Infrastructures (LRIs), offering opportunities for collaboration, optimization of experimental approaches, and informed decision-making by governmental and funding bodies.

The random fluctuations of spins give rise to many interesting physical phenomena, such as the ‘order-from-disorder’ arising in frustrated magnets and unconventional Cooper pairing in magnetic superconductors. Here we show that the exchange of spin waves between extended topological defects, such as domain walls, can result in novel magnetic states. We report the discovery of an unusual incommensurate phase in the orthoferrite TbFeO 3 using neutron diffraction under an applied magnetic field. The magnetic modulation has a very long period of 340 Å at 3 K and exhibits an anomalously large number of higher-order harmonics. These domain walls are formed by Ising-like Tb spins. They interact by exchanging magnons propagating through the Fe magnetic sublattice. The resulting force between the domain walls has a rather long range that determines the period of the incommensurate state and is analogous to the pion-mediated Yukawa interaction between protons and neutrons in nuclei. The interaction between spins in magnetic materials gives rise to a number of interesting effects. An example is the discovery of an unusual magnetic state based on a long-range ordering force between magnetic domain walls that is analogous to the interaction between protons and neutrons in atomic nuclei.

The quasi-2D platinum-based rare earth intermetallic LaPt 2 Si 2 has attracted attention as it exhibits strong interplay between charge density wave order and superconductivity. However, most of the results reported on this material come from theoretical calculations, preliminary bulk investigations and powder samples, which makes it difficult to uniquely determine the temperature evolution of its crystal structure and, consequently, of its charge density wave transition. Therefore, the published literature around LaPt 2 Si 2 is often controversial. Here, by means of high-resolution synchrotron X-ray diffraction data, we clarify some of the poorly or partially understood aspects of the physics of LaPt 2 Si 2 . In particular, we resolve the complex evolution of its crystal structure and superstructures, identifying the temperature dependence of multiple density wave transitions in good quality LaPt 2 Si 2 single crystals. According to our findings, on cooling from room temperature LaPt 2 Si 2 undergoes a series of subtle structural transitions which can be summarised as follows: second order commensurate tetragonal ( P 4/ n m m )-to-incommensurate structure followed by a first order incommensurate-to-commensurate orthorhombic ( P m m n ) transition and then a first order commensurate orthorhombic ( P m m n )-to-commensurate tetragonal ( P 4/ n m m ). The structural transitions are accompanied by both incommensurate and commensurate superstructural distortions of the lattice. The observed behavior is compatible with discommensuration of the CDW in this material. LaPt 2 Si 2 exhibits an intriguing interplay of superconductivity and charge density wave order, but the nature of its density wave transitions is controversial. Here, high-resolution X-ray diffraction reveals the temperature dependence of a series of density wave and structural transitions in this material.

Previous studies of elliptical neutron guides have shown that they transport neutrons with fewer reflections than traditional guides with a constant cross section, thus reducing neutron losses. True elliptical guides, however, are tedious to produce. Therefore, we use the neutron simulation package McStas to investigate the effect of approximating the elliptical shape by linearly tapering guide pieces. The study concerns both simple model guides and a more complex guide system corresponding to that of the BIFROST instrument, currently under construction at the European Spallation Source (ESS). Our results show that it is possible to split a simple elliptical guide into linearly tapering pieces with lengths of up to 3 m, without sacrificing transport properties. We also find that the piecewise tapering guides in some cases will have a slightly higher neutron transfer than the perfectly shaped guides for shorter wavelengths. For a ballistic guide systems with elliptical expanding and focusing sections, and for the BIFROST guide, linearly tapered pieces of 0.5 m can be used with no cost in transport properties or penalties in form of inhomogeneous phase space, but with significantly lower production costs.

We model the effect of ground movement, based on empirical experience, on the transport properties of long neutron guides by ray-tracing simulations. For a simple model, our results reproduce the large losses found by an earlier study, while for a more realistic engineering model of guide mounting, we find the losses to be significantly smaller. A detailed study of the guide for the cold neutron spectrometer BIFROST at the European Spallation Source shows that a realistic loss value is 7.0(5)% for wavelengths of 2.3–4.0 Å, the typical operational wavelength range of the instrument. This amount of loss does not call for mitigation by overillumination as suggested in the previous work. Our work serves to quantify the robustness of the transport properties of long neutron guides, in construction or planning at neutron facilities worldwide.