Hydrogen absorption significantly alters the mechanical properties of steel. However, absorbed hydrogen also influences its electronic and magneto-structural properties, helping to interpret how hydrogen is incorporated. This study therefore investigates the influence of hydrogen incorporation on the electronic and magneto-structural properties of X2CrNi18-9 stainless steel in different microstructural states. Microstructural characterization included analytic electron microscopy mapping, X-ray diffraction and thermodynamic stability maps to evaluate grain size, dislocation density and chemical homogeneity. The electronic properties were characterized using the Seebeck coefficient, while the magneto-structural properties were investigated using diffuse neutron scattering and small-angle neutron scattering (SANS). Hydrogen incorporation showed clear changes in the Seebeck coefficients. Magnetic SANS in conjunction with diffuse neutron scattering indicates the existence of nanoscale inhomogeneities with the same fcc structure as the bulk, but with correlation lengths of a few nanometres. The size of these inhomogeneities increased with hydrogen incorporation, suggesting that hydrogen preferentially accumulates in their vicinity. However, no direct correlation between the electronic and magneto-structural properties and the dislocation density could be demonstrated. We suggest that studies such as these will lead in the medium term to the development of guidelines for material design to make steels more resistant to hydrogen.

The addition of Graphene Nano Sheets (GNS) to Sn-Ag alloys presents a promising approach for enhancing leadfree solder materials, aiming to improve structural integrity and mechanical properties for electronic applications. In this study, we investigate the microstructural evolution and property enhancements in a Sn-Ag-GNS composite using Small-Angle Neutron Scattering (SANS), X-Ray Diffraction (XRD), and Electron Backscatter Diffraction (EBSD) techniques. SANS analysis indicates that the specific surface area of the Sn-Ag-GNS composite increased from 2.4 m2/g in the base Sn-Ag alloy to 3.2 m2/g with the addition of GNS-a 25% rise that reflects the introduction of additional interfaces by the graphene. Furthermore, the fractal dimension (Df) decreased from 3.0 to 2.7, pointing to the development of rougher and more intricate interfacial structures that can enhance crack resistance and overall toughness. Such a reduction in fractal dimension reflects increased interfacial roughness, which is known to promote crack deflection and tortuous crack paths, thereby enhancing energy dissipation and resistance to crack propagation. The incorporation of GNS also disrupts the initial crystallographic texture, leading to a more isotropic grain orientation, which in turn promotes uniform mechanical behavior in all directions. Together, these findings demonstrate that GNS significantly improves the microstructure of Sn-Ag alloys by introducing refined grain structures, enhanced interfacial complexity, and increased isotropy, which are microstructural features commonly associated with enhanced mechanical performance and reliability in Sn-based solder systems. This study underscores the potential of GNS-reinforced Sn-Ag alloys as high-performance, lead-free solder materials suitable for modern electronic applications.

The origin of double-step magnetization reversal processes, so-called wasp-waist magnetization hysteresis loops, in single magnetic phase 3D cobalt ferrite nanoassemblies is still poorly understood. So far, this behavior has been mainly attributed to the co-existence of hard-soft magnetic phases and spin canting in nanoparticles. Here, we demonstrate the wasp-waisted magnetization loops in single-phase flower-like Co0.82Fe2.18O4 nanoassemblies that were synthesized by modifying the ligand chemistry. Combining magnetization hysteresis loops at different concentrations, degrees of dipolar interactions, and temperatures, energy dispersive X-ray and in-field Mössbauer spectroscopy, and small-angle neutron scattering, we propose that a combination of a strong dipolar field and spin disordered nano-building blocks, leading to soft magnetic phase at the grain boundaries, accounts for this anomalous and abrupt drop in magnetization in nanoassemblies. The nanoassemblies have a porous nanostructure with nanogaps between their nano-building blocks, as revealed from electron microscopy investigations. Small-angle neutron scattering studies reveal spin disorder at the surface and interfaces of the nano-building blocks. The strong dipolar field at the ensemble level is only achieved when particle colloidal suspensions are dried from high particle concentrations, indicating concentration-dependent nature of this behavior. Single-core nanoparticles with a comparable chemical composition, effective size, coercive field, and magnetization, but with a coherent crystal structure, do not reveal this peculiar behavior even at highest concentrations. This finding demonstrates the role that the assembly of nanoscale building blocks plays to give rise to this peculiar magnetization. Our study introduces organic capping ligands as a novel means to tune magnetization processes in nanoparticles and to initiate new applications, a novel role for organic ligands beyond giving nanoparticles colloidal stability.

Phase behaviour and wetting properties of negatively charged silica nanosuspensions are influenced strongly by polyethylene oxide-polypropylene oxide-polyethylene oxide based non-ionic surfactants, known popularly as Pluronics. These triblock copolymers are adsorbed at silica nanoparticle surfaces and impart inter-particle attraction driven re-entrant liquid-liquid phase separations in silica nanosuspensions. The association characteristics of Pluronics at silica surfaces that lead to such behaviours are, however, not clearly understood yet. To shed light on this, we carried out dynamic light scattering (DLS), small-angle neutron scattering (SANS) and rheological studies on Ludox® LS-Pluronic systems comprising both hydrophobic Pluronic P123 and its hydrophilic counterpart, Pluronic F127. Our contrast matched SANS studies show that micelles formed by Pluronics in these systems remain correlated even at Pluronic concentrations as low as 1-2 wt%, which has not been observed hitherto in non-ionic micellar systems. Our DLS, SANS and rheological studies also show that evolutions of Pluronics induced inter particle attractions in LS nanosuspensions with Pluronic concentration and temperature differ significantly for the two Pluronics due to their widely different hydrophilic-lipophilic balances (HLB). Re-entrant transitions of repulsive-to-attractive-to-repulsive (or less attractive) state of inter particle interactions are thus observed as a function of temperature in the case of hydrophobic Pluronic P123 but as a function of Pluronic concentration in the case of hydrophilic Pluronic F127. The results give a comprehensive idea about the role of the association characteristics of Pluronics at the silica nanoparticle surface in influencing the properties of silica nanosuspensions.

Introduction of non-DLVO forces by nonionic surfactants brings about fascinating changes in the phase behavior of silica nanosuspensions. We show here that alterations in the interaction and wetting properties of negatively charged silica nanoparticles (Ludox (R) LS) in the presence of polyethylene oxide-polypropylene oxide-polyethylene oxide-based triblock copolymers called Pluronics lead to the formation of stable o/w Pickering emulsions and interparticle attraction-induced thermoresponsive liquid-liquid phase separations. The results make interesting comparisons with those reported for Ludox (R) TM nanosuspensions comprising larger silica nanoparticles. Association of these nanosystems with Pluronics occurs through their surface silanol groups. LS nanoparticles with a higher surface-to-volume ratio thus need a higher amount of Pluronics for the onset of interparticle attraction as compared to their TM counterparts. Small-angle X-ray scattering studies reveal that unlike TM nanosuspensions, LS nanosuspensions form Pickering emulsions with the ordering of both Pluronic-coated and bare nanoparticles at the oil-water interface. This could arise due to steric limitations in accommodating large Pluronic molecules between smaller LS nanoparticles, with highly curved surfaces, in closed-packed configurations. Small angle neutron scattering studies show clear signatures of the onset of thermoresponsive intermicellar attraction in these systems as a function of temperature and Pluronic concentration, induced solely by the modulation of non-DLVO steric and hydrophobic interactions, not reported hitherto in charged nanosuspensions. The results give insights into the roles of hydrophilic-lipophilic balance of surfactants and size of silica nanoparticles in determining the phase behaviors of silica-surfactant nanocomposite systems.

A quasi-binary two-dimensional Ising critical system with the main components D2O and butyric acid confined by surfactant layers has been studied. The surfactant forms large planar layers and is the basis of the charge density waves with wave fronts aligned with the layers. To orient the domains in an external magnetic field, thulium ions were added to the system (replacing sodium in the surfactant with thulium and adding more TmCl3). The critical behavior of the forward scattering and the correlation length were observed to be more mean-field-like. This can be explained by the presence of the trivalent thulium ions mediating between water and butyric acid. The high-Q scattering could be distinguished in the different directions and the ideal two-dimensional critical composition fluctuation exponent ηxy = 1/4 was observed, while the other exponent ηz = −0.08 ± 0.06 was slightly negative due to a finite acceptance angle and the finite magnetic field. The orientationally averaged high-Q exponent x of this study is well-explained by ηxy = 1/4 of the two-dimensional Ising behavior and ηz = 0.

We experimentally report a hitherto unseen angular anisotropy in the polarized small-angle neutron scattering (SANS) cross section of a magnetically strongly inhomogeneous material. Based on an analytical prediction using micromagnetic theory, the difference between the spin-up and spin-down SANS cross sections is expected to show a spin-disorder-induced anisotropy. The effect is particularly pronounced in inhomogeneous magnetic materials, such as nanoporous ferromagnets, magnetic nanocomposites, or steels, which exhibit large nanoscale jumps in the saturation magnetization at internal pore-matrix or particle-matrix interfaces. Analysis of the experimental neutron data constitutes a method for determining the exchange-stiffness constant. Our results for the nuclear-magnetic interference terms contained in the polarized magnetic neutron scattering cross section might also be of relevance to other neutron techniques.

Designing well-defined magnetic nanomaterials is crucial for various applications and it demands a comprehensive understanding of their magnetic properties at the microscopic level. In this study, we investigate the contributions to the total anisotropy of Mn-Co mixed spinel nanoparticles. By employing neutron measurements sensitive to the spatially resolved surface anisotropy with sub-\AA\space resolution, we reveal an additional contribution to the anisotropy constant arising from shape anisotropy and interparticle interactions. Our findings shed light on the intricate interplay between chemical composition, microstructure, morphology, and surface effects, providing valuable insights for the design of advanced magnetic nanomaterials for AC biomedical applications, such as cancer treatment by magnetic fluid hyperthermia.

Designing well-defined magnetic nanomaterials is crucial for various applications and it demands a comprehensive understanding of their magnetic properties at the microscopic level. In this study, we investigate the contributions to the total anisotropy of Mn-Co mixed spinel nanoparticles. By employing neutron measurements sensitive to the spatially resolved surface anisotropy with sub-Åresolution, we reveal an additional contribution to the anisotropy constant arising from shape anisotropy and interparticle interactions. Our findings shed light on the intricate interplay between chemical composition, microstructure, morphology, and surface effects, providing valuable insights for the design of advanced magnetic nanomaterials for AC biomedical applications, such as cancer treatment by magnetic fluid hyperthermia.

Designing well-defined magnetic nanomaterials is crucial for various applications, and it demands a comprehensive understanding of their magnetic properties at the microscopic level. In this study, we investigate the contributions to the total anisotropy of Mn/Co mixed spinel nanoparticles. By employing neutron measurements sensitive to the spatially resolved surface anisotropy with sub-& Aring; space resolution, we reveal an additional contribution to the anisotropy constant arising from shape anisotropy and interparticle interactions. Our findings shed light on the intricate interplay among chemical composition, microstructure, morphology, and surface effects, providing valuable insights for the design of advanced magnetic nanomaterials for AC biomedical applications, such as cancer treatment by magnetic fluid hyperthermia.

The formation of reverse microemulsions (RMs) of spherical shape in the oil/water/surfactant ternary mixture at high molar ratio of water to surfactant (ω) is well established. Using dynamic light scattering, small-angle X-ray and neutron scattering, we elucidate the formation of non-spherical reverse microemulsions stabilised by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at ω = 10 and volume fractions of the dispersed phase, Φ, ranging from 0.005 to 0.20. In addition, we propose a strategy to tune the aspect ratio of non-spherical droplets and colloidal interactions by (i) varying the volume fraction of the dispersed phase (ii) changing the temperature, and (iii) by substituting the aliphatic oil with a mixture of aliphatic and aromatic hydrocarbons. This tunability of anisotropy along with a precise control of the interactions in the RMs, their ability to form spontaneously and their thermodynamic stability is crucial to provide a handle on reaction kinetics, synthesis of anisotropic nanoparticles as well as for their application as lubricants and viscosity modifiers.

We employ micromagnetic simulations to model the effect of pore-type microstructural defects on the magnetic small-angle neutron scattering cross section and the related pair-distance distribution function of spherical magnetic nanoparticles. Our expression for the magnetic energy takes into account the isotropic exchange interaction, the magnetocrystalline anisotropy, the dipolar interaction, and an externally applied magnetic field. The signatures of the defects and the role of the dipolar energy are highlighted and the effect of a particle-size distribution is studied. The results serve as a guideline to the experimentalist.

Tuning the core-shell morphology of bimagnetic nanoparticles and its associated exchange bias behavior is a promising way to overcome the superparamagnetic limit and stabilize the particle moment in extended time and temperature ranges. The intraparticle magnetization distribution and magnetic coupling between the two phases, however, is still unclear. We report a significant nonzero magnetization in the CoxFe(1-x)O core of native core-shell bimagnetic nanoparticles that is typically considered antiferro-or paramagnetic. Co0.14Fe0.86O@Co0.4Fe2.4O4 (6 nm@2 nm) and Co0.08Fe0.92O@Co0.58Fe2.28O4 (12 nm@2 nm) core-shell nanoparticles have been synthesized by thermal decomposition of a mixed cobalt-iron oleate with a similar Fe/Co distribution throughout the nanoparticle. We determine the exact phase composition and the magnetization distribution in the core and shell using a combination of X-ray and neutron small-angle scattering. Core and shell magnetization are traced separately with a varying magnetic field. Our results reveal that the magnetization of the core and the spinel-type shell phases are coupled at room temperature, i.e., rotating coherently with the magnetic field. This is a mandatory condition to observe a significant exchange bias effect at low temperatures. These findings highlight the enormous potential of finite size and exchange coupling in bimagnetic nanoparticles to control the magnetic properties via interface-induced magnetization.

The ability to modulate the size, the nanostructure, and the macroscopic properties of water-in-oil microemulsions is useful for a variety of technological scenarios. To date, diverse structures of water-in-alkane microemulsions stabilized by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) have been extensively studied. Even though the decisive parameter which dictates the phase behavior of micremulsions is the nature of the continuous phase, relatively very few reports are available on the structure and interactions in the microemulsions of aromatic oil. Here, we present a fundamental investigation on water-in-xylene microemulsions using small-angle neutron scattering (SANS) at a fixed molar ratio (ω) of water to AOT. We elucidate the microstructural changes in the water-AOT-xylene ternary system at dilute volume fractions (Φ = 0.005, 0.01, 0.03), where the droplet-droplet interactions are absent, to moderately concentrated systems (Φ = 0.05, 0.10, 0.15, and 0.20), where colloidal interactions become important. We also characterize the reverse microemulsions (RMs) for thermally induced microstructural changes at six different temperatures from 20 to 50 °C. Depending on the magnitude of Φ, the scattering data is found to be well described by considering the RMs as a dispersion of droplets (with a Schulz polydispersity) which interact as sticky hard spheres. We show that while the droplet diameter remains almost constant with increase in the volume fraction, the attractive interactions become prominent, much like the trends observed for water-in-alkane microemulsions. With increase in temperature, the RMs showed a marginal decrease in the droplet size but no pronounced dependence on the interactions was observed with the overall structure remaining intact. The fundamental study on a model system presented in this work is key to understanding the phase behavior of multiple component microemulsions as well as their design for applications at higher temperatures, where the structure of most RMs breaks down.

The magnetic field-induced actuation of colloidal nanoparticles has enabled tremendous recent progress towards microrobots, suitable for a variety of applications including targeted drug delivery, environmental remediation, or minimally invasive surgery. Further size reduction to the nanoscale requires enhanced control of orientation and locomotion to overcome dominating viscous properties. Here, control of the coherent precession of hematite spindles via a dynamic magnetic field is demonstrated using nanoscale particles. Time-resolved small-angle scattering and optical transmission measurements reveal a clear frequency-dependent variation of orientation and rotation of an entire ensemble of non-interacting hematite nanospindles. The different motion mechanisms by nanoscale spindles in bulk dispersion resemble modes that have been observed for much larger, micron-sized elongated particles near surfaces. The dynamic rotation modes promise hematite nanospindles as a suitable model system for field-induced locomotion in nanoscale magnetic robots.

Magnetic nanoparticles offer unique potential for various technological, biomedical, or environmental applications thanks to the size-, shape- and material-dependent tunability of their magnetic properties. To optimize particles for a specific application, it is crucial to interrelate their performance with their structural and magnetic properties. This review presents the advantages of small-angle X-ray and neutron scattering techniques for achieving a detailed multiscale characterization of magnetic nanoparticles and their ensembles in a mesoscopic size range from 1 to a few hundred nanometers with nanometer resolution. Both X-rays and neutrons allow the ensemble-averaged determination of structural properties, such as particle morphology or particle arrangement in multilayers and 3D assemblies. Additionally, the magnetic scattering contributions enable retrieving the internal magnetization profile of the nanoparticles as well as the inter-particle moment correlations caused by interactions within dense assemblies. Most measurements are used to determine the time-averaged ensemble properties, in addition advanced small-angle scattering techniques exist that allow accessing particle and spin dynamics on various timescales. In this review, we focus on conventional small-angle X-ray and neutron scattering (SAXS and SANS), X-ray and neutron reflectometry, gracing-incidence SAXS and SANS, X-ray resonant magnetic scattering, and neutron spin-echo spectroscopy techniques. For each technique, we provide a general overview, present the latest scientific results, and discuss its strengths as well as sample requirements. Finally, we give our perspectives on how future small-angle scattering experiments, especially in combination with micromagnetic simulations, could help to optimize the performance of magnetic nanoparticles for specific applications.

The small-angle neutron scattering data of nanostructured magnetic samples contain information regarding their chemical and magnetic properties. Often, the first step to access characteristic magnetic and structural length scales is a model-free investigation. However, due to measurement uncertainties and a restricted q range, a direct Fourier transform usually fails and results in ambiguous distributions. To circumvent these problems, different methods have been introduced to derive regularized, more stable correlation functions, with the indirect Fourier transform being the most prominent approach. Here, the indirect Fourier transform is compared with the singular value decomposition and an iterative algorithm. These approaches are used to determine the correlation function from magnetic small-angle neutron scattering data of a powder sample of iron oxide nanoparticles; it is shown that with all three methods, in principle, the same correlation function can be derived. Each method has certain advantages and disadvantages, and thus the recommendation is to combine these three approaches to obtain robust results.

On the basis of Brown's static equations of micromagnetics, the uniaxial polarization of the scattered neutron beam of a bulk magnetic material is computed. The approach considers a Hamiltonian that takes into account the isotropic exchange interaction, the antisymmetric Dzyaloshinskii-Moriya interaction, magnetic anisotropy, the dipole-dipole interaction and the effect of an applied magnetic field. In the high-field limit, the solutions for the magnetization Fourier components are used to obtain closed-form results for the spin-polarized small-angle neutron scattering (SANS) cross sections and the ensuing polarization. The theoretical expressions are compared with experimental data on a soft magnetic nanocrystalline alloy. The micromagnetic SANS theory provides a general framework for polarized real-space neutron methods, and it may open up a new avenue for magnetic neutron data analysis on magnetic microstructures.

Shell ferromagnetism is a new functional property of certain off-stoichiometric Ni-Mn-In Heusler alloys, with a potential application in non-volatile magnetic memories and recording media. One key challenge in this field remains the determination of the structural and magnetic properties of the nanoprecipitates that are the result of an annealing-induced segregation process. Thanks to its unique mesoscopic length scale sensitivity, magnetic small-angle neutron scattering appears to be a powerful technique to disclose the microstructure of such annealing-induced nanoprecipitates. In this study, the microstructure of a zero-field-annealed off-stoichiometric Ni50Mn45In5 Heusler alloy is investigated by unpolarized magnetic small-angle neutron scattering. The neutron data analysis reveals a significant spin-misalignment scattering, which is mainly related to the formation of annealing-induced ferromagnetic nanoprecipitates in an antiferromagnetic matrix. These particles represent a source of perturbation which, due to dipolar stray fields, gives rise to canted spin moments in the surroundings of the particle-matrix interface. The presence of anticorrelations in the computed magnetic correlation function reflects the spatial perturbation of the magnetization vector around the nanoprecipitates. The magnetic field dependence of the zero crossing and the minima of the magnetic correlation function are qualitatively explained using the law of approach to ferromagnetic saturation for inhomogeneous spin states. More specifically, at remanence, the nanoprecipitates act magnetically as one superdefect with a correlation length that lies outside the experimental q range, whereas near saturation the magnetization distribution follows each individual nanoprecipitate. Analysis of the neutron data yields an estimated size of 30 nm for the spin-canted region and a value of about 75 nm for the magnetic core of the individual nanoprecipitates.