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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.

Journal of radioanalytical and nuclear chemistry (2021). doi:10.1007/s10967-021-08102-2, Published by Springer Science + Business Media B.V., Dordrecht [u.a.]

The objective of this study was to demonstrate the feasibility of localising and detecting hydrate plugs inside submarine pipelines, in situ and contactless, using neutron-induced analytical techniques. Cold and fast neutron-beam instruments at Heinz Maier-Leibnitz Zentrum (MLZ) were used to show that neutrons penetrate through the thick wall and the insulation of such pipes and even the induced gamma radiation can be detected outside to perform a non-destructive chemical analysis within the pipe. It was found that the change in the hydrogen concentration caused by a possible hydrate plug can be detected in seconds; while with a detailed analysis at a given spot lasting for a few hours, it is possible to unambiguously identify the hydrate phase inside the hydrocarbon phase.

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.

Iron oxide nanoparticles are presently considered as main work horses for various applications including targeted drug delivery and magnetic hyperthermia. Several questions remain unsolved regarding the effect of size onto their overall magnetic behavior. One aspect is the reduction of magnetization compared to bulk samples. A detailed understanding of the underlying mechanisms of this reduction could improve the particle performance in applications. Here we use a number of complementary experimental techniques including neutron scattering and synchrotron X-ray diffraction to arrive at a consistent conclusion. We confirm the observation from previous studies of a reduced saturation magnetization and argue that this reduction is mainly associated with the presence of antiphase boundaries, which are observed directly using high-resolution transmission electron microscopy and indirectly via an anisotropic peak broadening in X-ray diffraction patterns. Additionally small-angle neutron scattering with polarized neutrons revealed a small non-magnetic surface layer, that is, however, not sufficient to explain the observed loss in magnetization alone.

New actively shielded asymmetric vertical field split-coil superconducting magnet with maximal field of 8 T has been recently procured and implemented on the beam line POLI at Maier-Leibnitz Zentrum (MLZ). The magnet is designed in order to facilitate the single crystal diffraction with polarised neutrons. In order to provide high neutron polarisation in the vicinity of the new strong magnet a dedicated compact-size solid-state supermirror bender polariser optimised for the short neutron wavelength on POLI has been built. A Mezei flipper, which had been previously developed for lower field, could be upgraded with additional guide fields in order to be used in combination with new polarizer and magnet. All components are discussed and the performance test for the entire setup is presented. High efficiency of the new polarised neutron diffraction setup on POLI is demonstrated. Polarized neutron diffraction experiments in the fields up to 8 T are now available at MLZ.

The field-induced ordering of concentrated ferrofluids based on spherical and cuboidal maghemite nanoparticles is studied using small-angle neutron scattering, revealing a qualitative effect of the faceted shape on the interparticle interactions as shown in the structure factor and correlation lengths. Whereas a spatially disordered hard-sphere interaction potential with a short correlation length is found for ∼9 nm spherical nanoparticles, nanocubes of a comparable particle size exhibit a more pronounced interparticle interaction and the formation of linear arrangements. Analysis of the anisotropic two-dimensional pair distance correlation function gives insight into the real-space arrangement of the nanoparticles. On the basis of the short interparticle distances found here, oriented attachment, i.e. a face-to-face arrangement of the nanocubes, is likely. The unusual field dependence of the interparticle correlations suggests a field-induced structural rearrangement.

By controlling the chemical composition and the spatial organization of nanoparticles, hybrid nanocomposites incorporating ordered arrangements of nanoparticles could be endowed with exotic physical and chemical properties to fulfill demands in advanced electronics or energy-harvesting devices. However, a simple method to fabricate hybrid nanocomposites with precise control of nanoparticle distribution is still challenging. We demonstrate that block copolymer-based nanocomposites containing well-ordered nanoparticles with various morphologies can be readily obtained by adjusting the nanoparticle concentration. Moreover, the structural evolution of nanocomposite thin films as a function of nanoparticle loading is unveiled using grazing-incidence transmission small-angle X-ray scattering and atomic force microscopy. The morphological transformation proceeds through a phase transition from perforated lamellae to in-plane cylinder layout, followed by structural changes. The successful achievement of a variety of morphologies represents an effective and straightforward approach to producing functional hybrid nanocomposites for potential applications in various functional devices.

The bosonic analogs of topological insulators have been proposed in numerous theoretical works, but their experimental realization is still very rare, especially for spin systems. Recently, two-dimensional (2D) honeycomb van der Waals ferromagnets have emerged as a new platform for topological spin excitations. Here, via a comprehensive inelastic neutron scattering study and theoretical analysis of the spin-wave excitations, we report the realization of topological magnon insulators in CrXTe

Applied physics / A 127(8), 576 (2021). doi:10.1007/s00339-021-04713-4, Published by Springer, New York

The manipulation of magnetic states in nanoparticle supercrystals promises new pathways to design nanocrystalline magnetic materials and devices. Trench-patterned silicon substrates were used as templates to guide the self-assembly of iron oxide nanoparticles. Grazing incidence small angle X-ray scattering shows that the nanoparticles form a long-range ordered structure along the trench direction while in the direction perpendicular to the trenches, no coherent structure is observable. Electron holography provides evidence of an ordered magnetic state of nanoparticle moments in the remanent state after the application of a saturation magnetic field parallel to the trenches. However, a disordered magnetic state was observed in a perpendicular geometry. Hysteresis loops indicate that the nanoparticle moments form a superferromagnetic state for the geometry parallel to the trenches. Memory effect investigations reveal that the disordered magnetic state corresponds to a collective superspin glass state in the perpendicular geometry, while the superferromagnetic state in the parallel geometry suppresses the superspin glass state.

The High-Brilliance Neutron Source project (HBS) aims at developing a medium-flux accelerator-driven neutron source based on a 70 MeV, 100 mA proton accelerator. The concept optimizes the facility such that it provides high-brilliance neutron beams for instruments operating at different time structures. This can be realized by generating an interlaced proton pulse structure, which is unraveled and sent to three different target stations by a multiplexer system. In the following we present the developments of a multiplexer system at the JULIC accelerator at Forschungszentrum Jülich GmbH (FZJ), which serves as test facility for HBS. The main components of the JULIC multiplexer system are designed to be scalable to the HBS parameters.

Small : nano micro (2104356), (2021). doi:10.1002/smll.202104356, Published by Wiley-VCH, Weinheim

Advanced materials 33(24), 2008683 (2021). doi:10.1002/adma.202008683, Self‐assembly of iron oxide nanoparticles (IONPs) into 1D chains is appealing, because of their biocompatibility and higher mobility compared to 2D/3D assemblies while traversing the circulatory passages and blood vessels for in vivo biomedical applications. In this work, parameters such as size, concentration, composition, and magnetic field, responsible for chain formation of IONPs in a dispersion as opposed to spatially confining substrates, are examined. In particular, the monodisperse 27 nm IONPs synthesized by an extended LaMer mechanism are shown to form chains at 4 mT, which are lengthened with applied field reaching 270 nm at 2.2 T. The chain lengths are completely reversible in field. Using a combination of scattering methods and reverse Monte Carlo simulations the formation of chains is directly visualized. The visualization of real‐space IONPs assemblies formed in dispersions presents a novel tool for biomedical researchers. This allows for rapid exploration of the behavior of IONPs in solution in a broad parameter space and unambiguous extraction of ​the parameters of the equilibrium structures. Additionally, it can be extended to study novel assemblies formed by more complex geometries of IONPs., Published by Wiley-VCH, Weinheim

Antiphase boundaries (APBs) in iron oxide nanoparticles are studied by means of simulations. A strong influence on the spin structure is determined with Monte Carlo simulations, while hkl-dependent peak broadening useful for identifying APBs in real samples is found from Debye scattering equation simulations., Iron oxide nanoparticles find a wide variety of applications, including targeted drug delivery and hyperthermia in advanced cancer treatment methods. An important property of these particles is their maximum net magnetization, which has been repeatedly reported to be drastically lower than the bulk reference value. Previous studies have shown that planar lattice defects known as antiphase boundaries (APBs) have an important influence on the particle magnetization. The influence of APBs on the atomic spin structure of nanoparticles with the γ-Fe2O3 composition is examined via Monte Carlo simulations, explicitly considering dipole–dipole interactions between the magnetic moments that have previously only been approximated. For a single APB passing through the particle centre, a reduction in the magnetization of 3.9% (for 9 nm particles) to 7.9% (for 5 nm particles) is found in saturation fields of 1.5 T compared with a particle without this defect. Additionally, on the basis of Debye scattering equation simulations, the influence of APBs on X-ray powder diffraction patterns is shown. The Fourier transform of the APB peak profile is developed to be used in a whole powder pattern modelling approach to determine the presence of APBs and quantify them by fits to powder diffraction patterns. This is demonstrated on experimental data, where it could be shown that the number of APBs is related to the observed reduction in magnetization.

Thin solid films 735, 138862 (2021). doi:10.1016/j.tsf.2021.138862, Published by Elsevier, Amsterdam [u.a.]

This paper reports on the formation of large area, self assembled, highly ordered monolayers of stearyl alcohol grafted silica nanospheres of ≈50 nm diameter on a silicon substrate based on the drop-casting method. Our novel approach to achieve improved order uses stearyl alcohol as an assistant by adding it to the colloidal NanoParticle (NP) dispersion from which the monolayers are formed. Additionally, a heat treatment step is added, to melt the stearyl alcohol in the monolayer and thereby give the particles more time to further self-assemble, leading to additional improvement in the monolayer quality. The formation of the monolayers is significantly affected by the concentration of the NPs and the stearyl alcohol, the volume of the drop as well as the time of the heat treatment. A high surface coverage and uniform monolayer film of SiO

Magnetic thin films and multilayers offer many novel physical phenomena with tremendous potential for applications. Various growth processes and methods are in place to make homogeneous films. However, dispersion in local easy axes is an inherent issue which may give rise to an effective random anisotropy in thin film. It is important to investigate the effect of random anisotropy on the magnetic properties of the thin films. In this report we address the aspect of local dispersion induced random anisotropy on magnetization reversal in ferromagnetic (FM)/non-magnetic(NM)/ferromagnetic(FM) stacks. We show that the magnetization reversal is not only governed by the inter-layer interaction but the intrinsic anisotropies also play a crucial role. In this context we have studied the magnetization reversal of Co/ AlO X /Co trilayers with various thicknesses of AlO X which acts as a spacer between the two Co layers. Presence of random anisotropy in addition to growth induced uniaxial anisotropy was observed in all the samples. Magneto-optic Kerr effect (MOKE) based microscopy revealed dipolar-coupled layer-by-layer magnetization reversal of the Co layers which was corroborated by polarized neutron reflectometry (PNR) experiments. Micromagnetic simulations confirmed that the presence of random anisotropy in addition to uniaxial anisotropy leads to layer-by-layer magnetization reversal.

[8th International Meeting of the Union for Compact Accelerator-driven Neutron Sources, UCANS-8, 2019-07-08 - 2019-07-10, Paris, France] 8th International Meeting of the Union for Compact Accelerator-driven Neutron Sources, UCANS-8, Paris, France, 8 Jul 2019 - 10 Jul 2019; Les Ulis : EDP Sciences, The European physical journal / Web of Conferences Web of Conferences : proceedings proceedings 231, 04001 pp. (2020). doi:10.1051/epjconf/202023104001, Published by EDP Sciences, Les Ulis

[8th International Meeting of the Union for Compact Accelerator-driven Neutron Sources, UCANS-8, 2019-07-08 - 2019-07-10, Paris, France] 8th International Meeting of the Union for Compact Accelerator-driven Neutron Sources, UCANS-8, Paris, France, 8 Jul 2019 - 10 Jul 2019; Les Ulis : EDP Sciences, The European physical journal / Web of Conferences Web of Conferences : proceedings proceedings 231, 03006 pp. (2020). doi:10.1051/epjconf/202023103006, Published by EDP Sciences, Les Ulis

We report here a comprehensive study of the AFM structures of the Eu and Mn magnetic sublattices as well as the interplay between Eu and Mn magnetism in this compound by using both polarized and non-polarized single-crystal neutron diffraction. Magnetic susceptibility, specific heat capacity measurements and the temperature dependence of magnetic diffractions suggest that the AFM ordering temperature of the Eu and Mn moments is at 22 and 337 K, respectively. The magnetic moments of both Eu and Mn ions are oriented along the crystallographic $c$ axis, and the respective magnetic propagation vector is $\textbf{k}_{Eu} = (0,0,1)$ and $\textbf{k}_{Mn}=(0,0,0)$. With proper neutron absorption correction, the ordered moments are refined at 3 K as 7.7(1) $\mu_B$ and 4.1(1) $\mu_B$ for the Eu and Mn ions, respectively. In addition, a spin-flop (SF) phase transition of the Eu moments in an applied magnetic field along the $c$ axis was confirmed to take place at a critical field of B$_c$ $\sim$ 5.3 T. The evolution of the Eu magnetic moment direction as a function of the applied magnetic field in the SF phase was also determined. Clear kinks in both field and temperature dependence of the magnetic reflections ($\pm1$, 0, 1) of Mn were observed at the onset of the SF phase transition and the AFM order of the Eu moments, respectively. This unambiguously indicates the existence of a strong coupling between Eu and Mn magnetism. The interplay between two magnetic sublattices could bring new possibilities to tune Dirac fermions via changing magnetic structures by applied fields in this class of magnetic topological semimetals., Comment: 15 pages, 12 figures, accepted by Physical Review Research

Journal of radioanalytical and nuclear chemistry 325(2), 641-655 (2020). doi:10.1007/s10967-020-07271-w, Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

Organic aromatic cold neutron moderators - like mesitylene ( C 9 H 12 ) - are often much more convenient to handle and to commission than cryogenic methane or ortho/para hydrogen moderators. Although this benefit comes at the cost of reduced brilliance, mesitylene moderators are suited to enable cold neutron applications at sources where a complex traditional cold moderator system is not feasible. Developing the Julich High Brilliance neutron Source (HBS) project, we have investigated the use of such a low-dimensional mesitylene moderator with MCNP and ANSYS simulations and validated the simulations with experiments at TU Dresden's AKR-2 reactor. Here we will document the feasibility, advantages and drawbacks of such a system and give an outlook on future optimization potentials.

A rational use of superparamagnetic iron oxide nanoparticles (SPIONs) in drug delivery, diagnostics, and other biomedical applications requires deep understanding of the molecular drug adsorption/desorption mechanisms for proper design of new pharmaceutical formulations. The adsorption and desorption of the cytostatic Mitoxantrone (MTO) to lauric acid-albumin hybrid coated particles SPIONs (SEONLA−HSA) was studied by Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), surface titration, release experiments and small-angle neutron and X-ray scattering. Such MTO-loaded nanoparticles have shown very promising results in in vivo animal models before, while the exact binding mechanism of the drug was unknown. SEONLA−HSA formulations have shown better stability under drug loading in comparison with uncoated nanoparticle and sustainable drug release to compare with protein solution. Adsorption of MTO to SEONLA−HSA leads to decreasing of absolute value of zeta potential and repulsive interaction among particles, which points to the location of separate molecules of MTO on the outer surface of LA-HSA shell.

In the present work we demonstrate, how the self-assembly of nanoparticles provides a simple and straightforward way to fabricate ordered nanocomposites on length scales of up to 300…1000 µm. We realize this by employing a centrifugation assisted sedimentation technique. We start with magnetic iron oxide nanoparticles (NPs) with an average diameter of 15 nm, which are dispersed in toluene. The particles are coated with an organic shell to prevent unordered agglomeration of particles. After centrifugation and subsequent drying large macroscopic assemblies of NPs are obtained. The characterization of the samples using scanning electron microscopy (SEM), x-ray diffraction (XRD) and small angle x-ray scattering (SAXS) reveals that the samples are NP macro-polycrystals. By variation of the fabrication parameters as e.g. centrifugation speed and temperature we obtain a systematic study on how NP ordering, crystallinity and morphology depend on the fabrication parameters. Moreover, the magnetic properties of the NP macro-polycrystals are studied using superconducting quantum interference device (SQUID) magnetometry.

The advent of research reactors in the middle of the last century opened the opportunity for research with neutrons. Cliff Shull and Bert Brockhouse were awarded the Nobel prize for physics in 1994 for pioneering contributions to the development of neutron scattering techniques for studies of condensed matter. Since then, research with neutrons has emerged as an indispensable technique for materials research and development of functional materials, which is key to solving many of the grand challenges of our modern societies. With its broad user community, hierarchical structure of neutron sources and the Institute Laue-Langevin as the leading neutron facility, Europe has acquired an excellent standing in this field in terms of publication output. In its network of sources, the low flux sources provide the foundation by educating the next generation of neutron users and offer a platform for method development. Medium flux sources with broader instrumentation cover similar aspects, but additionally provide capacity and capability, e.g., by specializing in certain aspects like a distinctive sample environment or by addressing a specific local or regional user group. Finally, the flagship facilities are essential for the most demanding, flux-hungry experiments.

We present bulk and neutron scattering measurements performed on the isotopically enriched $^{154}\mathrm{Sm_2Ti_2O_7}$ and $^{154}\mathrm{Sm_2Sn_2O_7}$ samples. Both compounds display sharp heat capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron scattering measurements are employed to determine the crystalline electric field (CEF) level scheme, which includes transitions between the ground-state and first excited $J$ multiplets of the $\mathrm{Sm}^{3+}$ ion. To further validate those results, the single-ion magnetic susceptibility of the compounds is calculated and compared with the experimental DC-susceptibility measured in low applied magnetic fields. It is demonstrated that the inclusion of intermultiplet transitions in the CEF analysis is fundamental to the understanding of the intermediate and, more importantly, low temperature magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity anomaly is shown to correspond to the onset of an all-in-all-out long-range order in the stannate sample, while in the titanate a dipolar long-range order can be only indirectly inferred., 13 pages, 10 Figures

In ferromagnetic (FM) metal/organic semiconductor (OSC) heterostructures charge transfer can occur which leads to induction of magnetism in the non-magnetic OSC. This phenomenon has been described by the change in the density of states in the OSC which leads to a finite magnetic moment at the OSC interface and it is called the ‘spinterface’. One of the main motivations in this field of organic spintronics is how to control the magnetic moment in the spinterface. In this regard, there are several open questions such as (i) which combination of FM and OSC can lead to more moment at the spinterface? (ii) Is the thickness of OSC also important? (iii) How does the spinterface moment vary with the FM thickness? (iv) Does the crystalline quality of the FM matter? (v) What is the effect of spinterface on magnetization reversal, domain structure and anisotropy? In this context, we have tried to answer the last four issues in this paper by studying Fe/C60 bilayers of variable Fe thickness deposited on Si substrates. We find that both the induced moment and thickness of the spinterface vary proportionally with the Fe thickness. Such behavior is explained in terms of the growth quality of the Fe layer on the native oxide of the Si (100) substrate. The magnetization reversal, domain structure and anisotropy of these bilayer samples were studied and compared with their respective reference samples without the C60 layer. It is observed that the formation of spinterface leads to a reduction in uniaxial anisotropy in Fe/C60 on Si (100) in comparison to their reference samples.

The interface between the organic semiconductor (OSC)/ferromagnetic (FM) material can exhibit ferromagnetism due to their orbital hybridization. Charge/spin transfer may occur from the FM to OSC layer leading to the formation of “spinterface,” i.e., the interface exhibiting a finite magnetic moment. In this work, the magnetic properties of the Co / C 60 bilayer thin film have been studied to probe the interface between the Co and C60 layer. Polarized neutron reflectivity (PNR) measurement indicates that the thickness and moment of the spinterface are ∼2 ± 0.18 nm and 0.8 ± 0.2 μB/cage, respectively. The comparison of the magnetization reversal between the Co / C 60 bilayer and the parent single layer Co thin film reveals that spinterface modifies the domain microstructure. Further, the anisotropy of the bilayer system shows a significant enhancement (∼two times) in comparison to its single layer counterpart which is probably due to an additional interfacial anisotropy arising from the orbital hybridization at the Co / C 60 interface.The interface between the organic semiconductor (OSC)/ferromagnetic (FM) material can exhibit ferromagnetism due to their orbital hybridization. Charge/spin transfer may occur from the FM to OSC layer leading to the formation of “spinterface,” i.e., the interface exhibiting a finite magnetic moment. In this work, the magnetic properties of the Co / C 60 bilayer thin film have been studied to probe the interface between the Co and C60 layer. Polarized neutron reflectivity (PNR) measurement indicates that the thickness and moment of the spinterface are ∼2 ± 0.18 nm and 0.8 ± 0.2 μB/cage, respectively. The comparison of the magnetization reversal between the Co / C 60 bilayer and the parent single layer Co thin film reveals that spinterface modifies the domain microstructure. Further, the anisotropy of the bilayer system shows a significant enhancement (∼two times) in comparison to its single layer counterpart which is probably due to an additional interfacial anisotropy arising from the orbital ...

The magnetic-field-induced assembly of magnetic nanoparticles (NPs) provides a unique and flexible strategy in the design and fabrication of functional nanostructures and devices. We have investigated the field-induced self-assembly of core-shell iron oxide NPs dispersed in toluene by means of small-angle neutron scattering (SANS). The form factor of the core-shell NPs was characterized and analyzed using SANS with polarized neutrons. Large-scale aggregates of iron oxide NPs formed above 0.02 T as indicated by very-small-angle neutron scattering measurements. A three-dimensional long-range ordered superlattice of iron oxide NPs was revealed under the application of a moderate magnetic field. The crystal structure of the superlattice has been identified to be face-centred cubic.

[8th International Meeting of Union for Compact Accelerator-Driven Neutron Sources, UCANS-8, 2019-07-08 - 2019-07-10, Paris, France] 8th International Meeting of Union for Compact Accelerator-Driven Neutron Sources, UCANS-8, Paris, France, 8 Jul 2019 - 10 Jul 2019; Les Ulis : EDP Sciences, The European physical journal / Web of Conferences Web of Conferences : proceedings proceedings 231, 02002 pp. (2020). doi:10.1051/epjconf/202023102002, Published by EDP Sciences, Les Ulis

We present high-resolution thermal-expansion and specific-heat measurements of single crystalline α-RuCl

Scientific reports 8(1), 5515 (2018). doi:10.1038/s41598-018-23864-8, Published by Nature Publishing Group, London

We present high-resolution thermal-expansion and specific-heat measurements of single crystalline alpha-RuCl3. An extremely hysteretic structural transition expanding over 100 K is observed by thermal- expansion along both crystallographic axes, which we attribute to a change of stacking sequence of the RuCl3 layers. Three magnetic transitions are observed, which we link to the different stacking sequences. Using our data and thermodynamic relations, we derive the uniaxial and hydrostatic pressure derivatives of all three magnetic transitions. Our results demonstrate that magnetic order should be totally suppressed by very moderate pressures of 0.3 GPa to 0.9 GPa. Finally, we discuss why our results differ from recent hydrostatic pressure measurements and suggest a possible route to reaching the spin-liquid state in alpha-RuCl3., Comment: 6 pages, 3 figures

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

Inelastic neutron scattering measurements are performed on single crystals of the antiferromagnetic compound Mn_{5}Si_{3} in order to investigate the relation between the spin dynamics and the magnetothermodynamics properties. It is shown that, among the two stable antiferromagnetic phases of this compound, the high temperature one has an unusual magnetic excitation spectrum where propagative spin waves and diffuse spin fluctuations coexist. Moreover, it is evidenced that the inverse magnetocaloric effect of Mn_{5}Si_{3}, the cooling by adiabatic magnetization, is associated with field induced spin fluctuations.