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DiffMod is a simulation program for the evolution of a neutron ensemble in a thermal target – moderator – reflector assembly of a pulsed neutron source based on the statistical description of diffusion, scattering, moderation, and absorption processes. The spatial resolution, the energy resolution and the diffusion directions are strongly restricted to achieve calculation times in a realistic moderator – reflector assembly below 1 hour. In comparison with Monte-Carlo simulations describing the geometry and interactions between neutrons and moderator material exactly, we prove that the DiffMod approach can deliver intensities and pulse shapes that are exact within 10% compared to the Monte-Carlo simulations that require much more computing power. In addition, a time-resolved illustration of the spatial distribution of the neutrons at different energy levels is provided.

Compact accelerator-driven neutron sources allow to operate multiple optimised target-moderator-reflector (TMR) units adapted to the requirements of the respective instruments. The compact design of the TMR units allows an efficient coupling of neutron production, neutron moderation and extraction, but requires a novel way of optimisation. The neutronic performance of different TMR units based on polyethylene, heavy water and a mixture of heavy and light water moderators together with Pb and Be reflectors and a borated polyethylene absorber is discussed. Extraction channels for thermal and cold neutrons are investigated regarding the energy and time spectra.

This paper discusses the cleric Nikolaus Graurock († 1493), who came to Rome at a young age to embark upon a remarkable career. His connection to the Hospital and Fraternity of Santa Maria dellʼAnima was the first important support used by this man of legal and diplomatic talents, who thus became acquainted with the customs of the Curia and of Rome and was able to quickly build up a personal network. His membership of the familia of cardinal Latinus Orsini, who came from a family of the high nobility with influence in Rome and Italy, was also fundamental. In the 1450 s, Graurock was one of the key figures – especially in the „Lüneburg Prelate War“ – in the exchange between the Curia and representatives from northern Germany. Thanks to his position, however, Nikolaus Graurock also promoted the careers of others, including relatives. During his long stay in Rome he came into closer contact with those humanists who played an increasingly important role at the papal court from the second half of the 15th century onwards and whose works he later disseminated in Germany. This example of a mid-level cleric thus offers fundamental insights into the career opportunities that Rome and the Curia offered in the 15th century.

The nuclear and magnetic structures of Mn

With the construction of the ESS, the European neutron user community is eagerly awaiting the commissioning of the brightest neutron source worldwide in 2021. Parallel to this, there is however the ongoing development of neutron science being undertaken at a dwindling number of neutron facilities worldwide. The Julich Centre for Neutron Science has started a project to develop and design compact accelerator-driven high brilliance neutron sources as an efficient and cost effective alternative to the current low- and medium-flux reactor and spallation sources with the potential to offer science and industry access to neutrons. The project aims to deliver a high brilliance neutron source (HBS), consisting of a compact neutron production and moderator system which provides thermal and cold neutrons with high brilliance efficiently extracted in an optimized neutron transport system. By shaping the experiment holistically from the source to the detector, neutron experiments could be set-up for specific scientific requirements in a flexible and efficient way for the neutron user.

Low Energy accelerator-driven Neutron Facilities have the potential to become competitive to research reactors and spallation sources to generate neutron beams for scattering experiments. A low energy accelerator-driven neutron facility is developed at the Julich Centre for Neutron Science. This source is expected to provide thermal and cold neutrons with high brilliance and is therefore called “High Brilliance neutron Source” (HBS). In this work, we study the performance of neutron guide systems at HBS by using neutron ray-tracing simulations. Elliptical and ballistic guides with elliptic diverging/converging section have been used in simulations for various moderator-to-guide distances and guide entrance cross-sections. Results show that the beam properties have a strong dependence on the distance between guide entry and moderator. We demonstrate that the ballistic guide system can achieve a comparable neutron flux and brilliance transfer as the true elliptical guide for thermal neutrons if a proper distance between guide entrance and moderator is chosen. For low-divergence cold neutrons, the selected ballistic guide is showing even better performance than the elliptical one.

The crystal structure and magnetic properties of the materials FexNi8-xSi3 with 0 ≤ x ≤ 8 have been investigated to estimate any possible magnetocaloric effect and compare it to that in known magnetocalorics. Two structural ranges could be identified in this system by X-ray and neutron diffraction. The structure of the samples with 0 ≤ x ≤ 4 is related to the trigonal structure of Ni31Si12. Doubled c lattice parameters compared to the one in Ni31Si12 are observed in the samples with x = 2 and x = 3. The average structure of Fe2Ni6Si3 has been determined by X-ray single-crystal diffraction. The compounds with the compositions 5 ≤ x ≤ 8 crystallize in cubic Fe3Si-type structure. Magnetic measurements have shown that the compound Fe3Ni5Si3 displays a phase transition close to room temperature. However, its magnetocaloric effect is much smaller than the one in the promising magnetocaloric materials.

The lattice dynamics of orthorhombic Sb2Se3 is studied by a combination of inelastic neutron and 121Sb nuclear inelastic scattering giving access to the total and Sb partial density of phonon states (DPS). The Se partial DPS is determined from the difference between the total and Sb partial DPS. The total DPS is determined at 39, 150, and 300 K, and an analysis of the temperature‐induced mode shifts in combination with low‐temperature powder diffraction data is provided. Using an earlier reported theoretical approach, the corresponding total and partial DPS of Sb2Se3 are calculated by first‐principles calculations. Herein, a detailed analysis of the Grüneisen parameter, element‐specific and bulk Debye temperatures, and the mean force constants as derived from the experimental data and discrete Fourier transform calculations is provided. In general, the calculations underestimate the strength of the covalent SbSe bonds.

Journal of physics / Condensed matter Condensed matter 32(16), 165801 - (2020). doi:10.1088/1361-648X/ab678c, Published by IOP Publ., Bristol

The High-Brilliance Neutron Source (HBS) project aims to design a scalable compact accelerator driven neutron source (CANS) which is competitive and cost-efficient. The concept allows one to optimize the whole facility including accelerator, target, moderators and neutron optics to the demands of individual neutron instruments. Particle type, energy, timing, and pulse structure of the accelerator are fully defined by the requirements of a given neutron instrument. In the following, we present the current status of the HBS project., Proceedings of the 14th Int. Conf. on Heavy Ion Accelerator Technology, HIAT2018, Lanzhou, China

Über die Umstände von Entstehung und Rezeption eines der wichtigsten Texte der deutschen Mystik, Mechthilds „Fließendes Licht der Gottheit“ und seine lateinische Übersetzung, gab es bislang vor allem Mutmaßungen und Legendenbildungen. Diese waren insbesondere der schwierigen Überlieferung der beiden Fassungen geschuldet. Neuere Handschriftenfunde der letzten Jahre erlauben inzwischen präzisere Verortungen der beiden Texte und der Verfasserin Mechthild (von Magdeburg) im mitteldeutschen Raum. Der Band setzt hier an: Er leistet zum einen eine kritische Sichtung der gängigen Narrative, zum anderen bietet er aus unterschiedlichen disziplinären Perspektiven Ansätze zur Korrektur bisher gültiger Annahmen. Diese betreffen u.a. Mechthilds Status als (Laien-)Schwester im Kloster, die adligen und geistlichen Netzwerke, in denen das Kloster Helfta im 13. Jahrhundert steht; sie betreffen die intertextuellen Bezüge zwischen dem „Fließenden Licht“ und der zeitgenössischen geistlichen und weltlichen Literatur, den Sprachstand des „Fließenden Lichts“ sowie die spätmittelalterliche Rezeption der Helftaer Texte in mitteldeutschen Klöstern. Der Band stellt das „Fließende Licht“ und seine Rezeption damit erstmals in den Mittelpunkt der interdisziplinären Forschungsdiskussion. The circumstances of the origin and reception of one of the most important texts of German mysticism, Mechthild’s “Fließendes Licht der Gottheit” and its Latin translation, have so far been mainly the subject of speculation and legend. This was due to the difficult tradition of the two versions. However, the discovery of unknown manuscripts in recent years allow a more precise localisation of the two texts and the author Mechthild (of Magdeburg) in the area of central Germany. This is the starting point of the volume: On the one hand, it provides a critical review of the common narratives, and on the other hand, it offers approaches from different disciplinary perspectives to correct previously valid assumptions. These concern for example Mechthild’s status as a (lay) sister in a monastery, the aristocratic and spiritual networks in which Helfta Monastery was located in the 13th century; they concern the intertextual relationships between the “Fließende Licht” and contemporary spiritual and secular literature, the linguistic status of the “Fließende Licht” and the late medieval reception of the Helfta texts in central German monasteries. This volume thus places “Fließendendes Licht” and its reception at the centre of the interdisciplinary research discussion for the first time.

Low gradient magnetic holding fields are required for maintaining the polarization of polarized 3He, as diffusion though non-ideal gradients can cause total relaxation rates much greater than the intrinsic total 3He relaxation rate of a particular 3He cell in optimal conditions. For neutron scattering applications we often rely on µ-metal cavities to provide a degree of shielding from the many other sources of magnetic fields and gradient experienced on a typical neutron instrument. The JCNS utilizes two concepts for such cavities, one based on inexpensive plastic-bonded magnets to provide magnetic flux, and the other based on field coils wound on the sides of the µ-metal cavity. 2 different sized of permanent magnet cavities and three different geometries of coil-based cavities have been produced. Both types of boxes will be presented with magnetic design as well as mechanical construction details along with the achieved performance of the constructed devices.

12th International Conference on Polarised Neutrons for Condensed Matter Investigations, PNCMI 2018, Abingdon, UK, 3 Jul 2018 - 6 Jul 2018; Journal of physics / Conference Series 1316, 012009 (2019). doi:10.1088/1742-6596/1316/1/012009 special issue: "12th International Conference on Polarised Neutrons for Condensed Matter Investigations (PNCMI 2018) 3-6 July 2018, Abingdon, UK", Published by IOP Publ., Bristol

The thermal neutron time-of-flight spectrometer TOPAS will be equipped with a large detector system based on 2 meter long position sensitive 3He-tubes, each having an internal pressure of 10 bar 3He. In total there are 288 tubes with an overall active area of 14.7 m2. In order to decouple the detector from the vacuum chamber as well as to facilitate assembly and maintenance, the 3He-tubes are grouped on modular detector boxes. 16 tubes are mounted per detector box, which houses the digitizing readout electronics in a vacuum tight compartment at the back. During commisioning of the detector boxes, special emphasis has been put on the straightness of the tubes, as the planarity and parallelism of the their mounting points must ensure a straightness of below 1.2 mm. Additionally, the homogeneity of the signal amplitudes for neutron events has also been inspected, as the tube manufacturer pointed us to deficiencies of the wire quality at the time of the tube production. Measurements for the 3He-tube and detector box acceptance have been carried out with a moderated 252Cf-source. The signal amplitudes and event positions have been simultaneously taken and studied for the selection and adjustment of the tubes, which is reported in this paper.

Magnetic and structural properties of high quality magnetocaloric MnFe4Si3 single crystals are investigated macroscopically and on an atomic scale. Refinements of combined neutron and X-ray single crystal diffraction data introduce a new structural model in space group P6 characterized by partial ordering of Mn and Fe into layers perpendicular to c on one of the transition metal sites. A second transition metal site is exclusively occupied by iron. MnFe4Si3 has a phase transition to a ferromagnetically ordered phase at approximately 300 K and displays a strong anisotropy of the magnetization and the magnetocaloric effect with the easy axis of magnetization in the a,b-plane. This is confirmed by a refinement of the magnetic structure in the magnetic spacegroup Pm′, which shows that the spins on the sites with mixed occupancy of Mn and Fe are aligned in the a,b-plane. A significant magnetic moment for the site exclusively occupied by iron could not be refined. The thermal evolution of the lattice parameters...

We present a new guide-split concept for transporting cold and thermal neutrons to multiple instruments from a single beam port at a neutron facility without compromising the useful neutron brilliance notably for any of the instruments. Elliptical guides are capable of transporting an almost completely filled phase space within a large divergence (+/- 2 degrees for cold neutrons). It is therefore possible to place several secondary guides side by side pointing in slightly different directions using the end of a primary guide as a virtual source. The instruments placed at the secondary guides hence exploit different parts of the phase space transported by the primary guide. In addition, the resulting kink between the primary and secondary guide eliminates line of sight. Using ray-tracing simulations of three different set-ups (with two, four, and eight secondary guides) we show that it is possible to illuminate at least eight sample positions from one beam port with a brilliance transfer above 90% on each sample on a 150 m long instrument. This has been clone for a phase space volume comprised of an area of 1 x 1 cm(2) and a maximum divergence of +/- 0.5 degrees within a wavelength band of 425-5.75 angstrom. We show, by a full virtual experiment, an example of applying the guide-split concept to an instrument proposed for the European Spallation Source, namely a magnetism diffractometer. (C) 2015 Elsevier B.V. All rights reserved, (Less)

International Conference on Neutron Optics, NOP2017, Nara, Japan, 5 Jul 2017 - 8 Jul 2017; JPS conference proceedings 22, 011025 (2018). doi:10.7566/JPSCP.22.011025 special issue: "Proceedings of the International Conference on Neutron Optics (NOP2017)", Published by The Physical Society of Japan, Tokyo

An XYZ polarization analysis solution has been developed for the new thermal time-of-flight spectrometer TOPAS [1], to be operated in the coming east neutron guide hall at the MLZ. This prototype is currently being prepared to use on NEAT at HZB [2]. Polarization Analysis Studies on a Thermal Inelastic Spectrometer, commonly called PASTIS [3], is based on polarized 3He neutron spin filters and an XYZ field configuration for the sample environment and a polarization-preserving neutron guide field. The complete system was designed to provide adiabatic transport of the neutron polarization to the sample position on TOPAS while maintaining the homogeneity of the XYZ field. This complete system has now been tested on the polarized time-of-flight ESS test beam line V20 at HZB [4]. We present results of this test and the next steps forward.

The magnetic excitation spectrum of the magnetocaloric compound ${\mathrm{MnFe}}_{4}{\mathrm{Si}}_{3}$ has been investigated by means of polarized and unpolarized inelastic neutron scattering on single crystals. Spectra were collected in the ferromagnetic phase (${T}_{C}\ensuremath{\approx}305\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), as well as in the paramagnetic state, in order to understand the nature of the magnetism in ${\mathrm{MnFe}}_{4}{\mathrm{Si}}_{3}$. Spin-wave measurements at 1.5 K reveal a strong anisotropy of the magnetic exchange interactions along the (h00) and (00l) reciprocal directions of the hexagonal system, which also manifests itself in the $q$-dependent linewidths in the paramagnetic state. The correlation lengths indicate a short-range order, while the average linewidth is of the order of ${k}_{B}{T}_{C}$ pointing to a behavior typical of many ferromagnets. In addition, the in- and out-of-plane spin fluctuations are found to be isotropic around ${T}_{C}$ and can be suppressed by a magnetic field of 2 T.

We present a method to calculate the covariance matrix of wavevector-energy transfer for neutron time-of-flight direct geometry spectrometers, with both pulse shaping and monochromating choppers. As the definition of the wavevector transfer and of its components depends on the detector geometry and on the instrumental parameters, three different geometries have been analyzed: spherical, cylindrical with horizontal and vertical axis. The specific dependence of the matrix elements on the instrumental parameters is explicitly given. The results of example calculations are also presented and discussed.

In order to provide the large chemistry and materials science as well as the geosciences communities with a powerful tool for rapid data acquisition, a time-of-flight powder diffractometer to be installed at the new Munich reactor has been designed. The time-of-flight technique is expected to outperform a monochromator instrument by at least an order of magnitude in data acquisition time, particularly on small samples of less than a cubic centimetre. The construction of this innovative type of diffractometer utilizes modern components such as focusing super-mirror neutron guides, a four-unit high-speed disk chopper system and linear position-sensitive detectors covering a solid angle of about 2π steradian. The diffractometer design enables an easy enlargement of the focal spot size and is therefore equally well suited for the texture analysis of large geological and archaeological samples.

Einerseits sollen heutige Schulbucher Anlasse und Kontexte dafur bieten, dass Schuler selbstandig neues Wissen konstruieren 3- insbesondere an Entdeckungsaufgaben. Andererseits soll in Schulbuchern ein verbindliches mathematisches Wissen reprasentiert sein — etwa in Form eines Systems von Merksatzen, die durch Beweise miteinander vernetzt sind. Die Verbindung beider Anspruche kann mit Entdeckungsaufgaben gelingen, die Schuler veranlassen, auf dem Wege zur Entdeckung eines Satzes selbst eine latente Beweisidee zu gewinnen, die im spateren Beweis manifest wird. Diese Option wird im vorliegenden Aufsatz an Schulbuchseiten aus der Sekundarstufe I analysiert, auf der Grundlage von Begriffen aus der philosophischen Logik.

We report a comprehensive specific heat and inelastic neutron scattering study to explore the possible origin of multiferroicity in HoCrO$_3$. We have performed specific heat measurements in the temperature range 100 mK - 290 K and inelastic neutron scattering measurements were performed in the temperature range 1.5 - 200 K. From the specific heat data we determined hyperfine splitting at 22.5(2) $\mu$eV and crystal field transitions at 1.379(5) meV, 10.37(4) meV, 15.49(9) meV and 23.44(9) meV, indicating the existence of strong hyperfine and crystal field interactions in HoCrO$_3$. Further, an effective hyperfine field is determined to be 600(3) T. The quasielastic scattering observed in the inelastic scattering data and a large linear term $\gamma=6.3(8)$ mJmol$^{-1}$K$^{-2}$ in the specific heat is attributed to the presence of short range exchange interactions, which is understood to be contributing to the observed ferroelectricity. Further the nuclear and magnetic entropies were computed to be, $\sim$$17.2$ Jmol$^{-1}$K$^{-1}$ and $\sim$34 Jmol$^{-1}$K$^{-1}$, respectively. The entropy values are in excellent agreement with the limiting theoretical values. An anomaly is observed in peak position of the temperature dependent crystal field spectra around 60 K, at the same temperature an anomaly in the pyroelectric current is reported. From this we could elucidate a direct correlation between the crystal electric field excitations of Ho$^{3+}$ and ferroelectricity in HoCrO$_3$. Our present study along with recent reports confirm that HoCrO$_3$, and $R$CrO$_3$ ($R=$ Rare earth) in general, possess more than one driving force for the ferroelectricity and multiferroicity., Comment: 17 pages, 6 figures, published in J. Phys.: Condens. Matter

Proximity effects in an [Er20|Tb5] superlattice lead to the formation of new magnetic phases. Modulated magnetic order, expected for pure Er, and ferromagnetic order, expected for pure Tb, coexist at low temperatures. Employing X-ray resonance exchange scattering, we could probe directly the respective spin polarisations of the conduction band electrons, providing a mechanism for the interlayer coupling. The different anisotropies of Er and Tb compete with this tendency to long-range magnetic order, leading to substantial thermal-hysteresis effects.

© 2015 Owned by the authors, published by EDP Sciences. We report on the progress of the construction of the thermal time-of-flight spectrometer with polarization analysis TOPAS at the Mayer-Leibnitz Zentrum (MLZ). The instrument components approach the status to be ready for installation. The special feature of the instrument is its capability for wide-angle polarization analysis in the thermal spectral range. Here we describe a novel approach to rotate the neutron spin adiabatically into the X, Y or Z direction of the laboratory frame by combination of permanent magnets aligned as Halbach rings and electrically generated fields. Despite the severe spatial restrictions the design exhibits a very high adiabaticity and interacts only weakly with the coil layout for the analyzing 3He spin filter cell (SFC).

We have employed a new experimental configuration to measure ferromagnetic X-ray resonance exchange scattering (XRES) from a EuS single crystal. Using polarisation analysis we could achieve a magnetic-scattering intensity stronger than charge scattering resulting in an asymmetry ratio as large as Ra = 0.67 at the EuLII edge. By a combined refinement of the dependencies of the scattered intensity on the energy and the applied magnetic field we could uniquely determine spectroscopic information such as the 5d conduction band exchange splitting = 0.27(1) eV.

We re-investigate the magnetically frustrated, {\it diamond-lattice-antiferromagnet} spinels FeAl$_2$O$_4$ and MnAl$_2$O$_4$ using magnetization measurements and diffuse scattering of polarized neutrons. In FeAl$_2$O$_4$, macroscopic measurements evidence a "cusp" in zero field-cooled susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory effect} experiments provide results that do not conform with a canonical spin-glass scenario in this material. Through polarized neutron scattering studies, absence of long-range magnetic order down to 4~K is confirmed in FeAl$_2$O$_4$. By modeling the powder averaged differential magnetic neutron scattering cross-section, we estimate that the spin-spin correlations in this compound extend up to the third nearest-neighbour shell. The estimated value of the Land\'{e} $g$ factor points towards orbital contributions from Fe$^{2+}$. This is also supported by a Curie-Weiss analysis of the magnetic susceptibility. MnAl$_2$O$_4$, on the contrary, undergoes a magnetic phase transition into a long-range ordered state below $\approx$ 40~K, which is confirmed by macroscopic measurements and polarized neutron diffraction. However, the polarized neutron studies reveal the existence of prominent spin-fluctuations co-existing with long-range antiferromagnetic order. The magnetic diffuse intensity suggests a similar short range order as in FeAl$_2$O$_4$. Results of the present work supports the importance of spin-spin correlations in understanding magnetic response of frustrated magnets like $A$-site spinels which have predominant short-range spin correlations reminiscent of the "spin liquid" state., Comment: 10 pages, 10 figures, double-column, accepted in Phys. Rev. B, 2014

We report on the first results of a structural and magnetic investigation of Fe 1-x Co x /Mn/Fe 1-x Co x trilayers (x = 0-0.75). In situ low energy electron diffraction shows that Mn grows epitaxially on bcc Fe 1-x Co x (x ≤ 0.75) with a good crystallinity up to 30 A. Reflectivity and small angle diffuse scattering of synchrotron radiation reveal sharp interfaces, each of them having two lateral characteristic lengths in the height-height correlation function that differ by one order of magnitude. The long-range height-height correlation function is vertically correlated and the short-range one is not. From magneto-optical Kerr effect measurements, evidence for non-collinear coupling between Fe 1-x Co x layers (x = 0 and 0.5) was found for Mn spacer thicknesses below 12 A. Polarized neutron reflectometry performed at 300 K reveal a net magnetization of 0.8 ± 0.3 μ B /at in the Mn layer in Fe 0.5 Co 0.5 /Mn/Fe 0.5 Co 0.5 and no net magnetization in the Mn layer in Fe/Mn/Fe.

We present an exchange bias (EB) effect of variable size in La${}_{0.67}$Sr${}_{0.33}$MnO${}_{3\ensuremath{-}\ensuremath{\delta}}$ single and La${}_{0.67}$Sr${}_{0.33}$MnO${}_{3\ensuremath{-}\ensuremath{\delta}}$/SrTiO${}_{3}$ (LSMO/STO) bilayers grown on STO substrates. Samples have been prepared by pulsed laser deposition (PLD) and high-pressure sputter deposition (HSD) in oxygen atmosphere at different oxygen pressures. Increased out-of-plane lattice parameters of the LSMO layers and reduced Curie temperatures indicate oxygen deficiencies in the samples grown at lower oxygen pressures. We found an increase of the EB and the coercive fields with decreasing oxygen pressure, whereas the growth at high pressures does not lead to an EB effect. The depth-sensitive method of polarized neutron reflectometry (PNR) reveals a region with drastically reduced, maybe even completely vanishing net magnetization in the LSMO layer at the interface to STO in the exchange-biased samples, but not in the non-exchanged-biased one. It is suggested that an antiferromagnetic structure is formed in this part of the LSMO thin film, which causes the EB effect in this system. An explanation based on the strain-doping phase diagram of LSMO is provided. Thus our findings open a route for tuning the EB effect by changing the oxygen vacancy concentrations.

We demonstrate spin-spiral-induced ferroelectricity in epitaxial TbMnO${}_{3}$ films grown on YAlO${}_{3}$ substrates down to a film thickness of 6nm. The ferroelectric polarization is identified by optical second-harmonic generation. Using x-ray resonant magnetic scattering we directly prove the existence of a noncollinear magnetic structure in the ferroelectric phase and thus bulk-like multiferroicity. The electric-field-induced reversal of the magnetic domains along with the reversal of the ferroelectric polarization evidences the rigid coupling of magnetic and ferroelectric order and hence a ``giant'' magnetoelectric effect in the films.