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Defect structures of BaTiO3 nanoparticles annealed in the air and their correlation with magnetic properties have been studied. As main research techniques, complementary methods such as XPS and positron annihilation lifetime spectroscopy were used. It was found that low-temperature annealing creates additional oxygen vacancies in nanoparticles both inside and on the nanoparticle surface, and high-temperature annealing favors the reduction of Ti. These changes influence nanoparticle magnetism and occur due to the charge compensation process and grain growth mechanism. Performed studies show that complementary XPS and positron annihilation spectroscopy are the effective tools to determine nanoparticle surface defect structure, which can be used to fabricate new rare room-temperature multiferroics materials.

The supramolecular organization of the visual pigment rhodopsin in the photoreceptor membrane remains contentious. Specifically, whether this G protein-coupled receptor functions as a monomer or dimer remains unknown, as does the presence or absence of ordered packing of rhodopsin molecules in the photoreceptor membrane. Completely opposite opinions have been expressed on both issues. Herein, using small-angle neutron and X-ray scattering approaches, we performed a comparative analysis of the structural characteristics of the photoreceptor membrane samples in buffer, both in the outer segment of photoreceptor cells, and in the free photoreceptor disks. The average distance between the centers of two neighboring rhodopsin molecules was found to be ~5.8 nm in both cases. The results indicate an unusually high packing density of rhodopsin molecules in the photoreceptor membrane, but molecules appear to be randomly distributed in the membrane without any regular ordering.

The experience gained in the last 15 years of experimental studies of large-scale structures with the SANS instrument at the IBR-2 pulsed reactor in Dubna shows that some parameters of the spectrometer can be improved. In particular, it concerns reduction of the fast neutron and gamma backgrounds that limit the possibilities of studying weakly scattering objects. Another direction of improvement is to reduce a minimum momentum transfer value Q min to study objects with larger characteristic dimensions. The paper investigates several configurations of the SANS machine at IBR-2. The Monte Carlo codes are used to calculate the parameters of such virtual instruments. An optimal instrument structure is proposed.

Structure and orientational disorder of ammonium ions in the high-temperature phase I of ND4I were studied by reverse Monte Carlo and maximum entropy methods using powder neutron diffraction data. The ammonium ions were found to perform a librational motion with an average angular libration amplitude of γ=20° and reorientational motion by 39° jumps of the N–D bonds between (xxx) and (xxz) positions in the structure. Reorientations by 90° jumps were found to have a low probability.

The sequence of phase transitions at temperatures from 290 to 420 K in the crystals of Cs5H3(SO4)4·0.5H2O (CTSM) and Cs5D3(SO4)4·0.5D2O (DCTSM) was studied by Brillouin light scattering and neutron diffraction. Anomalies in the temperature dependences of the velocity and damping of hypersonic acoustic phonons in the vicinity of 360 K were observed in the CTSM crystal. In contrast, no anomalies were found in the DCTSM crystal. Preliminary analysis of neutron diffraction data does not show symmetry changes in the temperature range studied. Thus it has been found that deuteration of the CTSM crystals leads to a change in the sequence of phase transitions.

Neutron guides are widely used to transport the neutrons from the moderator to the sample. Due to the constructive features of the ring corridor of the fast pulsed reactor IBR-2, the minimal distance between the moderator and the guide entrance is around 6 m. The main goal of the paper is to optimize the neutron optical system between the moderator and the entrance of the new neutron guides. Using Monte Carlo simulations we calculate the possible best gain of the neutron flux density at the guide exit. After the described optimization process, the optimal system is obtained. The recommendations for construction of the new beam line are provided too. Similar technique and the proposed system could be easily adapted for another similar beam line at the neutron sources.

The structural and magnetic properties of iron nanoparticles formed in an aluminium matrix by combined helium and iron ions irradiation have been studied by small-angle X-ray scattering and susceptibility measurements. The formation of nanoparticles with average size of about 6.8 nm under iron ions irradiation has been found. The additional posterior irradiation with helium ions leads to the iron nanoparticles ordering with correlation length of 7.2(1) nm. The characteristic radius of iron nanoparticles and fractal dimension of the Al matrix were determined and magnetic properties of the Fe-Al nanomaterials were analysed.

Nonmagnetic particles in magnetized ferrofluids have been denoted magnetic holes and are in many ways ideal model systems to test various forms of particle self assembly and dynamics. Some case studies to be reviewed here include:Chaining of magnetic holesBraid theory and Zipf relation used in dynamics of magnetic microparticlesInteractions of magnetic holes in ferrofluid layersThe objectives of these works have been to find simple characterizations of complex behavior of particles with dipolar interactions.