Deutsche Neutronenstreutagung 2024

Europe/Berlin
Hörsaalgebäude PPS (Aachen)

Hörsaalgebäude PPS

Aachen

Professor Pirlet Str. 12 52074 Aachen The Postersession and Social Evening on the 17th of September will take place in the Forum M (Mayer'sche Buchhandlung), Buchkremerstraße 1-7, 52062 Aachen.
Registration
Deutsche Neutronenstreutagung 2024
Frau Laura Kleebank
    • Registration Foyer PPS

      Foyer PPS

    • Welcome PPS-1

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      Hörsaalgebäude PPS 1
    • Plenary Lecture: Walter Richtering - Can neutrons help understanding what softness means in soft matter? PPS-1

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    • Coffee Break Foyer PPS

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    • Session 1: Energy & Advanced Materials (Chairs: Matteo Bianchini, Jakob Schröder, Cecilia Solis, Anna Windmüller) PPS-1

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      Energy & Advanced Materials

      • 1
        Understanding aging mechanisms in Li-ion batteries

        Lithium-ion batteries are the popular choice for power sources in consumer electronics. As they have achieved a tremendous boost in their performance in the last decades, they are being increasingly employed in electrical vehicles and grid-scale energy storage systems as well.

        However, there is still room for improvement in terms of life expectancy, safety, cost, energy storage capabilities and interfacial stabilities. In this regard, understanding fundamental aging mechanisms that lead to capacity fade in Li-ion batteries becomes important to design batteries with improved components for performance enhancement.

        With help of several examples, this presentation will reveal how different aging contributors such as loss of electrochemically active Li, active material degradation, and Li metal deposition can be detected using neutrons and conventional lab-based methods. For each of these cases, I will demonstrate how we optimized electrode design with feedback from obtained data and enhanced cell performance by positively affecting key parameters such as lifetime, charging rate, energy density, interfacial stability, and safety.

        For example; using anodes containing mesocarbon microbeads instead of needle coke graphite we obtained faster charging capabilities and a longer lifetime [1]; by coating electrodes with polymers we achieved interfacial stability and obtained superior cycling performance [2]; by using Co-free cathodes and extending the operating voltage limits, we achieved both reductions in costs and increase in energy densities compared to conventional cathodes [3]; by incorporating silicon in anodes, we obtained increased energy densities compared to conventional anodes [4,5].

        [1] N. Paul, J. Wandt, S. Seidlmayer, S. Schebesta, M. J. Mühlbauer, O. Dolotko, Hubert A. Gasteiger, R. Gilles, Journal of Power Sources, 85, 345 (2017).
        [2] Z. Huang, S. Choudhury, N. Paul, J. H. Thienenkamp, P. Lennartz, H. Gong, P. Müller-Buschbaum, G. Brunklaus, R. Gilles, Z. Bao, Advanced Energy Materials, 12, 2103187 (2022).
        [3] N. M. Jobst, N. Paul, P. Beran, M. Mancini, R. Gilles, M. Wohlfahrt-Mehrens, P. Axmann, Journal of the American Chemical Society 145, 4450 (2023).
        [4] N. Paul, J. Brumbarov, A. Paul, Y. Chen, J.‐F. Moulin, P. Müller-Buschbaum,J. Kunze-Liebhäuser, R. Gilles, Journal of Applied Crystallography, 48, 444 (2015).
        [5] E. Moyassari, L. Streck, N. Paul, M. Trunk, R. Neagu, C.-C. Chang, S.-C. Hou, B. Märkisch, R. Gilles, A. Jossen, Journal of the Electrochemical Society, 168, 020519 (2021).

      • 2
        LiBH4 as a liquefying agent for a Li-Mg-N-H hydrogen storage system

        The hydrogen storage in light-weight hydrides for mobile applications is an extensively discussed but a rather controversial topic. Is it safe enough? Is it efficient enough? Does the hydrogen energy have future? The questions are numerous and complicated and hardly any of them has a definite answer yet. A complex hydride system 6Mg(NH2)2:9LiH with LiBH4 as a dopant is one of promising candidates on a role of on-board hydrogen storage, since it it actively decomposes with hydrogen-only emission already at the 180oC. The role of the LiBH4 is expressed in forming of an low-melting liquid-phase with high hydrogen mobility with an intermediate product LiNH2, which highly enhances the rate of the dehydrogenation reaction. There are 2 mixed phases with a high Li-ion conductivity described: a metastable Li2BH4NH2 and a peritectically melting Li4BH4(NH2)3, and both of these phases were registered while performing DSC and XRD measurements. This 2-component system is investigated and a number of ratios was analyzed and thereupon a phase diagram was plotted. Its lowest melting point, i.e. eutectic point is located at 33% LiNH2 and at 90oC. The behavior under heating and the intrinsic structure of this eutectic composition was investigated by neutron total scattering. The composition corresponding to this eutectic mixture would be 6Mg(NH2)2:9LiH:6LiBH4.

        Speaker: Anastasiia Thase (Kuznetsova) (Helmholtz-Zentrum Hereon, WPN)
      • 3
        Corannulene – A material of molecular rotors

        In light of the growing global demand for energy while the world is moving away from finite and polluting fossil fuels, new sources of energy and energy carriers need to be developed. Recovering waste heat is one viable route that can provide energy otherwise lost as thermal radiation. Novel carbon-based materials, such as corannulene and perylene, are promising candidates to be used as phase-change materials with thermal transitions inside the temperature ranges that are common to many large-scale industrial processes thus granting access to the 50 % or more of energy that is lost as heat [1].

        Corannulene specifically stands out for its versatility as an energy carrier. In the course of our studies, it was proven to not just be an adequate phase change material with a remarkable ability to be supercooled up to 80 K below the melting point on cooling at 10 K/min, but also to be able to store hydrogen [2]. We have, thus, embarked on a thorough exploration of corannulene's dynamic and structural behaviour across the solid, liquid and metastable supercooled phases as well as from ambient pressures to over 20 GPa using a range of techniques such as neutron scattering, thermoanalytical techniques, light-based methods and computer simulations. Our work has since shown that corannulene showcases a rich phenomenology with the emergence of dynamical disorder well below the nominal melting point of 540 K [3], also refer to Fig. 1.

        Building on these prior results, we have since shed more light onto the underlying mechanisms of corannulene's stochastic motions, tracking the emergence of three distinct relaxation modes spanning three orders of magnitude, which ultimately culminate in the melting of the molecule (cf. Fig. 2). Furthermore, we have developed a novel method allowing for measuring the glassification of corannulene, which was achieved at cooling rates upwards of 1000 K/s [4], the kinetic phase diagram of which is shown in Fig. 3. In this contribution, we will present the relationship between the molecule's kinetically-arrested, 'glassy' phase to the disorder and relaxation features that are noted in the crystalline solid. Moreover, we will demonstrate new insights gained by recent QENS experiments illustrating the liquid and supercooled phase of corannulene. Those serve to elucidate corannulene's ability to supercool consistently well below the melting point.

        [1] Renew. Sustain. Energy Rev. 38 164 (2014)
        [2] Carbon 155 432 (2019)
        [3] Carbon 183 196 (2021)
        [4] Thermochim. Acta 719 179414 (2023)

        Speaker: Balthasar Braunewell (CFM/MPC)
      • 4
        Neutron diffraction based residual stress analysis of additively manufactured alloys

        Additive manufacturing methods such as laser powder bed fusion offer an enormous flexibility in the efficient design of parts. In this process, a laser locally melts feedstock powder to build up a part layer-by-layer. It is this localized processing manner imposing large temperature gradients, resulting in the formation of internal stress and characteristic microstructures. Produced parts inherently contain high levels of residual stress accompanied by columnar grain growth and crystallographic texture. On a smaller scale, the microstructure is characterized by competitive cell-like solidification with micro segregation and dislocation entanglement. In this context, it is crucial to understand the interplay between microstructure, texture, and residual stress to take full advantage of the freedom in design. In fact, X-ray and neutron diffraction are considered as the benchmark for the non-destructive characterization of surface and bulk residual stress. The latter, characterized by a high penetration power in most engineering alloys, allows the use of diffraction angle close to 90°, enabling the employment of a nearly cubic gauge volume. However, the complex hierarchical microstructures produced by additive manufacturing present significant challenges towards the reliable characterization of residual stress by neutron diffraction. Since residual stress is not the direct quantity being measured, the peak shift imposed by the residual stress present in a material must be converted into a macroscopic stress. First, an appropriate lattice plane must be selected that is easily accessible (i.e., high multiplicity) and insensitive to micro strain accumulation. Second, a stress-free reference must be known to calculate a lattice strain, which can be difficult to define for the heterogeneous microstructures produced by additive manufacturing. Third, an appropriate set of diffraction elastic constants that relate the lattice strain to the macroscopic stress must be known.
        In this presentation, advancements in the field of residual stress analysis using neutron diffraction are presented on the example of the Ni-based superalloy Inconel 718. The effect of the complex microstructure on the determination of residual stress by neutron diffraction is presented. It is shown, how to deal with the determination of the stress-free reference. It is also shown that the selection of an appropriate set of diffraction elastic constants depends on the microstructure. Finally, the role of the crystallographic texture in the determination of the residual stress is shown.

      • 5
        Diffusivity Investigation of Hydrogen Isotopes in Flexible MOFs by Quasi-Elastic Neutron Scattering

        Kinetic-quantum-sieving-assisted H2:D2 separation in flexible porous materials is more effective than the currently used energy-intensive cryogenic distillation and girdle-sulfide processes for isotope separation. It is believed that material flexibility results in a pore-breathing phenomenon under the influence of external stimuli, which helps in adjusting the pore size and gives rise to the optimum quantum-sieving phenomenon at each stage of gas separation. However, only a few studies have investigated kinetic-quantum-sieving-assisted isotope separation using flexible porous materials. Here, we present the quasi-elastic neutron scattering (QENS) data showing a significantly faster diffusion of deuterium than hydrogen in a flexible pore structure, even at high temperatures. Unlike rigid structures, the extracted diffusion dynamics of hydrogen isotopes within flexible frameworks show that the diffusion difference between the isotopes increases with an increase in temperature confirmed by measured QENS data. Owing to this unique inverse trend, a new strategy can be proposed for achieving higher operating temperatures for efficient isotope separation utilizing a flexible metal-organic framework system.

        Speaker: Jitae Park (MLZ, TUM)
    • Session 2: Condensed Matter (Chairs: Werner Paulus, Holger Kohlmann & Simon Steinberg) PPS-2

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      Condensed Matter

      • 6
        Dynamics of citrate ligands and water molecules on the surface of iron oxide nanoparticles: a QENS study

        Surface functionalization is needed for synthesizing and controlling the properties of iron oxide nanoparticles (IONPs) in various applications for biomedicine, ferrofluids, or heterogeneous catalysis [1,2]. Yet, experimental investigations of interfacial properties such as the dynamics of ligand and water molecules near the nanoparticle surface have been scarce. Previously, quasielastic neutron scattering (QENS) was successfully used to access the dynamics of water molecules on surfaces of TiO2 and SnO2 nanoparticles [3]. QENS studies of ligand dynamics on the surface of nanoparticles have also emerged recently. Dodecanethiol on PbS nanoparticles and oleates on IONPs were shown to exhibit rotational motion [4,5]. However, the dynamics of citrate ligands on the surface of magnetic IONPs are largely unknown. We report on QENS experiments on 6 nm IONPs synthesized according to ref [6] and equilibrated at 8 % relative humidity in H2O (measured at IN16B, ILL) and D2O (measured at Emu, ANSTO). Energy-resolved measurements as well as elastic and inelastic fixed window scans were performed in the temperature range of 2 – 380 K, covering a Q-range of 0.19 – 1.83 Å-1. Given the complex quasielastic scattering signal including the magnetic nature of the IONPs, we demonstrate the power of fixed window scans in separating multiple, dynamic processes, thermal vibrations, magnetic relaxations, and hydrogen dynamics. Employing samples equilibrated in D2O allowed for distinguishing water and citrate motion. To create a complete dynamical model, we implemented a simultaneous fit approach for elastic and inelastic fixed window scans, as well as energy-resolved spectra at different temperatures. We observed that the introduction of additional datasets into a simultaneous fit routine increases the stability of the fit, allowing for the application of more complex models. Further, the Q-dependence of energy-resolved spectra shows, that citrate molecules only exhibit a rotational motion on the IONPs surface, while water diffuses translationally.

        [1] Y. Sahoo, et al., J Phys Chem B, 109, 3879–3885 (2005)
        [2] E. Amstad, et al., Nanoscale, 3, 2819 (2011)
        [3] E. Mamontov, et al., J. Phys. Chem. C, 111, 4328-41 (2007)
        [4] M. Jansen, et al., ACS Nano, 12, 20517-20526 (2021)
        [5] A. Sharma, et al., Chem. Phys., 156, 164908 (2022)
        [6] M. Eckardt, et al., ChemistryOpen, 9, 1214–122 (2020)

        Speaker: Maksim Plekhanov (RWTH Aachen University)
      • 7
        Tuning the physical properties of La0.7Sr0.3MnO(3-δ) via oxygen off-stoichiometry using assisted thermal vacuum annealing

        The physical properties of complex oxides can be tuned via controlling oxygen vacancies thus enabling potential applications. In La0.7Sr0.3MnO(3-δ) (LSMO), the topotactic phase transition from the Perovskite (PV, ABO3) phase to the layered oxygen-vacancy-ordered Brownmillerite (BM, ABO2.5) phase can be triggered by deoxygenation. Here, we employed polished Aluminum foils as oxygen getter during the thermal vacuum annealing and realized the PV-to-BM phase transition in both a strained LSMO thin film system and bulk-like unstrained LSMO powder system. For LSMO thin films, the structural changes were monitored using X-ray Diffraction. A metal-to-insulator and simultaneously a ferromagnetic-to-antiferromagnetic transition is found. The variation of the manganese oxidation state is characterized using X-ray Absorption Spectroscopy. Rutherford Backscattering Spectroscopy implies a manganese-deficient BM phase after annealing. This BM phase shows in the magnetization vs. temperature curves a peculiar peak above room temperature which cannot be explained within the usual AF ordering at low temperatures. For LSMO powder, the evolution of the crystal structure and spin structure at different oxygen-deficient states from PV to BM is investigated using neutron diffraction. The neutron diffraction study hints at a process including multiple transitions of the crystal structure and spin structure.

        Speaker: Mr Chenyang Yin (Heinrich Heine University Düsseldorf, Faculty of Mathematics and Natural Sciences, Düsseldorf, Germany. Jülich Centre for Neutron Science (JCNS-2), JARA-FIT, Forschungszentrum Jülich GmbH, Jülich, Germany.)
      • 8
        Monoclinic symmetry of the hcp-type ordered areas in bulk cobalt

        The gradual ferromagnetic spin reorientation in the hcp phase of cobalt between 230°C and 330°C reported for a Co single crystal [1] suggests that this phase cannot have a hexagonal symmetry [2,3]. This hypothesis is verified positively by synchrotron radiation diffraction and neutron diffraction on powder of cobalt [4]. The hexagonal close packed phase of cobalt (hcp-Co) is associated with numerous stacking faults while the face centered cubic phase of cobalt (fcc-Co) has considerably less stacking faults, as shown e.g. in [5,6]. The analysis of diffraction data has been done by using a specific set of Bragg peaks, which are not affected by the stacking faults. The crystal structure of the hcp-type ordered areas of cobalt is described by a monoclinic symmetry with the magnetic space group C2'/m', where the former hexagonal [001] axis is no longer perpendicular to the hexagonal layers. The hexagonal [001] and [010] axes make an angle equal α≈90.10(1)°, while the angle between in-plane [100] and [010] axes equals γ≈120.11(1)°. In addition, we report [4] a one order of magnitude smaller lattice mismatch in the hexagonal planes between hcp-Co and fcc-Co than the mismatch of about 0.5% between the hexagonal layers in hcp-Co and fcc-Co layers [5, 6]. Williamson-Hall analysis shows that microstrains are larger inside hexagonal planes than along the stacking faults direction [4]. Moreover, a higher content of the fcc-Co phase reduces microstrains in hcp-Co [4].
        [1] E. Bertaut, A. Delapalme and R. Pauthenet, Solid State Commun. 1 (1963) 81
        [2] R. Przeniosło, P. Fabrykiewicz and I. Sosnowska, Acta Cryst. A74 (2018) 705
        [3] P. Fabrykiewicz, R. Przeniosło and I. Sosnowska, Acta Cryst. A77 (2021) 327
        [4] P. Kozłowski, P. Fabrykiewicz, I. Sosnowska, F. Fauth, A. Senyshyn, E. Suard, D. Oleszak and R. Przeniosło, Phys Rev. B107 (2023) 104104
        [5] O. S. Edwards and H. Lipson, Proc. R. Soc. Lond. Ser. A-Math. Phys. Sci. 180 (1942) 268
        [6] O. Blaschko, G. Krexner, J. Pleschiutschnig, G. Ernst, C. Hitzenberger, H. P. Karnthaler and A. Korner, Phys. Rev. Lett. 60 (1988) 2800

        Speaker: Piotr Fabrykiewicz (RWTH Aachen and JCNS at MLZ)
      • 9
        Understanding the impact of cooperativity on barocaloric properties in spin crossover complexes with spectroscopic methods

        The barocaloric effect (BCE) is characterized as a thermal response (variation of temperature or entropy) in solid-state materials induced by external hydrostatic pressure and cooling technologies based on the BCE have emerged as a promising alternative to conventional vapor-compression cooling. Recently, spin crossover (SCO) transitions, where the low spin (LS) and high spin (HS) states can be switched by hydrostatic pressure, were proposed as a potential mechanism to generate outstanding BCE. The considerable overall entropy change across the SCO transition is primarily attributed to the significant change in lattice vibration, which is directly linked to the dynamic features.
        In this study, we correlate the structural changes of a classic SCO complex Fe(PM-BiA)2(NCS)2 (with PM = N-2’- pyridylmethylene and BiA = 4-aminobiphenyl) in the vicinity of a spin transition as functions of temperature and pressure with the dynamic properties and aim at a better understanding of the role of cooperativity on the transition. The two polymorphs of Fe(PM-BiA)2(NCS)2 are ideal in this respect, as the orthorhombic polymorph (Pccn) features a high cooperativity indicated by an abrupt transition, while the gradual transition in the monoclinic polymorph (P21/c) hints towards a low cooperativity. From the structural studies, we determined which intermolecular interactions (hydrogen bridges, π-π interactions, van der Waals interactions) play a key role at the spin transition in both polymorphs.
        We investigate the changes in dynamic features at the temperature- and pressure-induced spin transition using different spectroscopic methods on a wide range of energy and time scales in combination with ongoing ab-initio modelling. Raman and IR spectroscopy give access to the energy difference of vibrational energy levels in the molecules. The Fe-related phonon density of states in the monoclinic polymorph is obtained through nuclear inelastic scattering (NIS) to extract the Fe-related vibrational entropy change in the energy range well below 100 meV. The result from quasi-elastic neutron scattering (QENS) confirms the existence of dynamic disorder in the order of picoseconds corresponding to sub-meV energy. Our combined approach allows us to unravel the different entropy contributions (electronic, vibrational, configurational) to the overall entropy change at the spin transition.

        Speaker: Ji Qi (Forschungszentrum Jülich GmbH)
      • 10
        Pb<sub>12</sub>O<sub>19</sub> – ML-DFT-PDF crystal structure analysis from combined neutron and synchrotron total scattering data.

        Mixed valence lead oxide phases obtained at ambient pressure are reported by Byström [1] belonging to either black [2] or red minium [1, 3]. For red minium the composition of Pb3O4 is described without any variance in the number of oxygen atoms [1, 3]. The formula could therefore be written as Pb(II)2Pb(IV)O4, expressing the different oxidation states of lead. For the black minium Byström [1] proposed two structures, namely, α-PbOx and β-PbOx. Pure α-PbOx exits for 1.628 (~ Pb12O19.5) > x ≥ 1.475 (~ Pb12O17.7). For lower x, β-PbOx and red minium coexist in the range of x = 1.475 – 1.352 (~ Pb12O16.2). We synthesized phase pure Pb12O19 by decomposing PbO1.96(2) at 600 K for 1390 h, showing a dark brown color. Neutron time-of-flight (TOF) total scattering data (nPDF) were collected on the powder diffractometer POWGEN@SNS (Oak Ridge National Lab, USA) within the Proposal IPTS-20531 and respective synchrotron radiation data (xPDF) on the P02.1@Petra III (DESY, Germany) powder diffractometer at E = 59.78(3) keV (λ = 20.74(4) pm). The combined machine-learning (ML) – density function theory (DFT) – pair distribution function (PDF) approach [4] was used to refine the structure of Pb12O19 starting with an unbiased set of structural models using both neutron and X-ray PDF data sets at the same time. Based on the ML-DFT-xPDF-nPDF refinements a structure model with a 2x2x1 bigger unit cell compared to those reported by Byström [1] was found. Instead of the CaF2-type [1] derived arachno-cube like coordination of the lead atoms, which could hardly be described as strongly distorted octahedra, different coordination numbers were found, giving rise for differently pronounced stereo-chemical activities of the Pb 6s2 lone pairs and void channels in the structure which might be described with a triangular shape. The new crystal structure enables to additionally describe the non-explained weak reflections of the earlier findings [1].
        1] A. Byström, Arkiv Kemi Mineral. Geol. 20(4) (1945) 1-31.
        [2] M. Le Blanc, E. Eberius, Z. für Phys. Chem. 160A(1) (1932) 69-100.
        [3] S.T. Gross, J. Am. Chem. Soc. 65(6) (1943) 1107-1110.
        [4] M. Klove, S. Sommer, B.B. Iversen, B. Hammer, W. Dononelli, Adv Mater (2023) e2208220.

        Figure: PDF-Plots of the refinement of the Pb12O19 structure to the synchrotron (a) and neutron data (b).

        Speaker: Thorsten Gesing (University of Bremen, Institute of Inorganic Chemistry and Crystallography, Leobener Straße 7, D-28359 Bremen, Germany; University of Bremen, MAPEX Center for Materials and Processes, Bibliothekstraße 1, Universität Bremen, D-28359 Bremen, Germany)
    • Coffee Break Foyer PPS

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    • Prize Evening: Wolfram-Prandl Prize PPS-1

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    • Prize Evening: Instrumentation Prize PPS-1

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    • Plenary Lecture: Helmut Schober - Advances at ESS PPS-1

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    • Welcome Reception Foyer PPS

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    • Plenary Lecture: Johanna Jochum - TBA PPS-1

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      Convener: Johanna Jochum
    • Presentation of ENSA & LENS Hörsaalgebäude PPS

      Hörsaalgebäude PPS

      Aachen

      Professor Pirlet Str. 12 52074 Aachen The Postersession and Social Evening on the 17th of September will take place in the Forum M (Mayer'sche Buchhandlung), Buchkremerstraße 1-7, 52062 Aachen.
    • Coffee Break Foyer PPS

      Foyer PPS

    • Session 3: Magnetisim and Superconductivity (Chairs: Bella Lake & Lukas Beddrich) PPS-1

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      • 11
        Magnetic Morphology and Exchange-Coupling in Cobalt-Doped Iron Oxide Core-Shell Nanoparticles

        The exchange coupling in bimagnetic core-shell nanoparticles is a promising pathway to permanent magnetic materials [1]. For iron oxide core-shell nanoparticles, consisting of a wuestite-like particle core and a spinel-type shell, transition metal doping was recently shown to significantly enhance the magnetic anisotropy and exchange coupling [2]. Native iron oxide core-shell nanoparticles synthesized by thermal decomposition of iron oleate typically form as an intermediate through topotaxial oxidation of an initial wuestite phase towards highly defective maghemite [3]. We have recently reported how the combination of such native core-shell nanoparticles (with their alignment of core and shell phases) and cobalt doping leads to a significant enhancement of the exchange pinning between both phases, which is promising for a rational synthesis of nanoparticles with strong coercivity and exchange field. Using magnetic SANS [4,5], we have unambiguously revealed a significant net magnetization even in the wuestite-type nanoparticle core that is commonly presumed antiferromagnetic or paramagnetic at room temperature [6].

        In this contribution, we will present the systematic influence of a subtle variation in particle size on the exchange coupling within such native core-shell, Co-doped iron oxide nanoparticles. For freshly synthesized samples with a particle diameter ranging from 8.5 to 9.6 nm, a clear transition from exchange spring to exchange bias behavior is evident. We employ magnetic SANS to elucidate the intraparticle magnetization individually for the wuestite-like particle core and the spinel-type shell and to follow their coupling mechanism.

        References:

        [1] A. López-Ortega et. al., Phys. Rep. 553, 1−32 (2015).
        [2] B. Muzzi et. al., Small 18, 2107426 (2022).
        [3] E. Wetterskog et al., ACS Nano 7, 7132–7144 (2013).
        [4] S. Mühlbauer, S. Disch, A. Michels et al., Rev. Mod. Phys. 91, 015004 (2019).
        [5] D. Zákutná, S. Disch et al., Phys. Rev. X 10, 031019 (2020).
        [6] D. Zákutná, N. Rouzbeh, S. Disch et al., Chem. Mater. 35, 2302–2311 (2023).

      • 12
        Going to Extraordinary Lengths in Superconducting Vortex Matter

        In the superconductor niobium the vortex-vortex interaction exhibits in addition to the purely repulsive also an attractive term. This leads to the formation of the intermediate mixed state (IMS) where flux-free Meissner state domains and mixed state domains filled with vortex lattice coexist separated on the micrometer length scale. Besides being a prominent example of exotic vortex matter this two-phase structure can also act as a highly tunable model system for universal domain physics as both the intervortex distance and the domain structure can be tuned via the magnetic field and temperature [1].
        Small angle neutron scattering (SANS) is the ideal tool to study the Bragg peaks from the vortex lattice with inter-vortex distances of 100-200 nm. Given the rough upper limit in SANS of 1 micrometer it struggles to capture the diffuse scattering from the domain boundaries with sizes of up to 50 micrometers. However, the power-law tail of the diffuse scattering extends into the SANS regime and contains valuable information about the domain structure. Conventionally, the power-law of diffuse scattering is analyzed using the Porod law connecting the scattering intensity to the specific surface area of randomly distributed scattering particles [2]. We show that in the specific case of the IMS, where the domain boundaries are close to parallel to the direct beam, the specific surface area can be interpreted as an inverse length corresponding to the size of the domain structure [3]. Using this approach, that takes into account the alignment of the domain boundaries along the beam direction to extract the correct specific surface area, we are able to extend the accessible length scales from 1 micrometer to up to 40 micrometers using a standard SANS setup.
        Our results fit well with Landau's theory of superconducting domains [4], previous attempts of extracting this length scale using ultra small angle neutron scattering [5] and highlight the power of our approach of extending the accessible length in SANS to the micrometer regime. Our analysis approach should be applicable to other two-phase systems where the domain boundaries are close to parallel to the incoming neutron beam.
        [1] A. Backs et al., Phys. Rev. B 100, 064503 (2019).
        [2] G. Porod, Small angle X-ray scattering, pp. 15–51. Academic Press (1982).
        [3] X. Brems et al., in preparation (2024).
        [4] L. Landau, JETP, 7, 371 (1937).
        [5] T. Reimann et al. Phys. Rev. B 96, 144506 (2017).

        Speaker: Xaver Simon Brems (Institut Laue-Langevin | Heinz Maier-Leibnitz Zentrum)
      • 13
        Magnetic order in the topological Kagome metals RMn6Sn6 (R= Dy, Gd, Yb)

        RMn6Sn6 (R=Gd-Lu, and Y) family is a subject of current interest owing to its Mn-Kagome lattice, which can host exotic topological quantum states and frustrated magnetism [1]. Tuning the rare-earth ions in RMn6Sn6, where R is magnetic, can engineer the topological transport properties, including quantum oscillation and the anomalous Hall effect (AHE) [2, 3], thus indicating a close relationship between the localized rare-earth magnetism and topological band structures. In this talk, we will present our recent investigations on three representative systems: for R without spin-orbit coupling L=0 (GdMn6Sn6), for R with spin-orbit coupling J=L+S (DyMn6Sn6), and for R with mixed valances (YbMn6Sn6). We mainly used single-crystal hot-neutron diffraction to solve the magnetic structures to reduce the neutron absorption by the natural Gd and Dy elements. Our refinement of the magnetic structure shows that GdMn6Sn6 exhibits a ferrimagnetic order. Interestingly, the DyMn6Sn6 exhibits ferrimagnetic order with spin reorientation behavior. Distinguishably, neutron diffraction on YbMn6Sn6 (with mixed Yb2+and Yb3+ valances) reveals a ferromagnetic order of the Mn moments, but without the ordering of the Yb ions, indicating that the Yb is non-magnetic. Our studies clearly suggest that the magnetic anisotropy of the rare-earth ion (R) plays a crucial role in controlling the spin orientation of the Mn kagome layers. The solved magnetic structures will help further in gaining more understanding of the underlying physics and its correlation with the topological properties in this family.

      • 14
        Distorting an antiferromagnetic kagome lattice: Magnetism of single-crystalline clinoatacamite

        The spin-$1/2$ Heisenberg model on the antiferromagnetic kagome lattice is one of the fundamental models in frustrated quantum magnetism with a predicted quantum spin liquid (QSL) ground state, spinon excitations and a complex sequence of magnetization plateaus in applied magnetic fields [1-3]. From an experimental viewpoint, the mineral herbertsmithite with uniform couplings in the kagome layer stands out as candidate material featuring a QSL ground state [4]. Recent advances in quantum magnetism also explicitly cover deformed kagome lattices leading to many different motifs of non-uniform exchange couplings containing novel physics (see, for instance, Refs. [5,6]).

        Here, we present a combined experimental and theoretical study on clinoatacamite, Cu$_2$Cl(OH)$_3$ [7], a mineral which is closely related to herbertsmithite. By means of density-functional theory we have derived the dominant magnetic exchange paths in this material forming non-uniform antiferromagnetic kagome layers of Cu sites with weak ferromagnetic coupling to the interlayer Cu site. Experimentally, we have investigated the zero-field magnetic phase diagram of clinoatacamite by means of thermodynamic measurement techniques as well as neutron diffraction using for the first time single-crystalline material. In agreement with earlier studies, we have found a transition of little entropic change at $T_\mathrm{N} = 18.1~\mathrm{K}$ (with an order parameter developing below this temperature) [8]. Further, we have resolved for the first time a sequence of two close-lying transition anomalies at $6.2$ and $6.4~\mathrm{K}$, which leads to a large entropy change in the material. We have refined the magnetic structure at $1.7~\mathrm{K}$ based on single-crystal neutron diffraction data and present inelastic neutron scattering results revealing the low-energy spin excitations in the same temperature region.

        [1] C. Broholm et al., Science 367, eaay0668 (2020).
        [2] L. Balents, Nature 464, 199 (2010).
        [3] S. Nishimoto et al., Nat. Commun. 4, 2287 (2013).
        [4] P. Khuntia et al., Nat. Phys. 16, 469 (2020).
        [5] O. Janson et al., Phys. Rev. Lett. 117, 037206 (2016).
        [6] K. Matan et al., Nat. Phys. 6, 865 (2010).
        [7] J. D. Grice et al., Can. Mineral. 34, 73 (1996).
        [8] X. G. Zheng et al., Phys. Rev. Lett. 95, 057201 (2005).

        Speaker: Leonie Heinze (Jülich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum, Germany)
      • 15
        Quantum dynamics in spin ice Ho2GaSbO7 due to structural disorder

        Rare earth pyrochlores offer a rich landscape for discovering and studying new states of matter due to the geometrical frustration imposed by their lattice structure. A notable example is the classical spin ice state found in Dy₂Ti₂O₇ and Ho₂Ti₂O₇, which exhibits infinite degeneracy.

        Even more intriguing is the concept of Quantum Spin Ice (QSI), where quantum tunneling between degenerate ice states realizes quantum electrodynamics. Quantum effects in QSI can be introduced through transverse interactions between Ising spins. Pyrochlore compounds containing elements such as Ce, Pr, Nd, and Yb are proposed candidates for exhibiting such behaviors. Another promising route to achieving QSI is by introducing effective transverse fields. These fields arise from lifting the accidental doublet degeneracy of the crystal field ground state of non-Kramers ions, such as Ho³⁺.

        Ho₂GaSbO₇, characterized by Ga/Sb disorder, is an ideal candidate for exploring this second route. Here, we report our studies on Ho₂GaSbO₇ using both macroscopic measurements and neutron scattering methods. The specific heat capacity of Ho₂GaSbO₇ shows a broad peak at 1.5 K, accompanied by a nuclear Schottky anomaly at lower temperatures, suggesting an absence of a transition to long-range magnetic order. This behavior is very similar to that observed in Ho₂Ti₂O₇.

        Furthermore, crystal field excitations in Ho₂GaSbO₇ were observed to be significantly broader than the instrument resolution, a consequence of the structural disorder. The elastic scattering profile shows intensity modulation characteristic of spin ice, while broad low-energy magnetic excitations below 0.8 meV were observed at 1.5 K. This observation starkly contrasts with classical spin ice and hints at the presence of quantum dynamics within the system.

        Speaker: Jianhui Xu
    • Session 4: Instrumentation and Data Management I (Chairs: Tobias Neuwirth & Artur Gregor Glavic) PPS-2

      PPS-2

    • Lunch Foyer PPS

      Foyer PPS

    • Plenary Lecture: Serena Cussen - TBA PPS-1

      PPS-1

    • Plenary Lecture: Christian Pfleiderer - Status and Future of FRM II PPS-1

      PPS-1

    • Coffee Break Foyer PPS

      Foyer PPS

    • Session 5: Instrumentation & Data Management II (Chairs: Tobias Neuwirth & Artur Gregor Glavic) PPS-1

      PPS-1

    • Session 6: Health and Life (Chairs: Tobias Schrader & Emanuel Schneck) PPS-2

      PPS-2

    • Transfer to Forum M
    • Mounting Posters, Beer and light Dinner Forum M (Mayersche Buchhandlung)

      Forum M

      Mayersche Buchhandlung

    • Session 7: Sources and Upgrades (Chairs: Wiebke Lohstroh & Paul Zakalek) PPS-1

      PPS-1

    • Session 8: Soft Matter (Chairpersons: Franziska Gröhn & Max Hohenschutz) PPS-2

      PPS-2

    • Coffee Break Foyer PPS

      Foyer PPS

    • Plenary Lecture: Stephan Förster - HBS PPS-1

      PPS-1

    • Plenary Lecture: Andreas Meyer - ILL Hörsaalgebäude PPS

      Hörsaalgebäude PPS

      Aachen

      Professor Pirlet Str. 12 52074 Aachen The Postersession and Social Evening on the 17th of September will take place in the Forum M (Mayer'sche Buchhandlung), Buchkremerstraße 1-7, 52062 Aachen.
    • Closing Ceremony PPS-1

      PPS-1

    • Tour of the JULIC Neutron Platform (HBS Test Stand): 13:30 - 16:30 at Forschungszentrum Jülich