In fundamental experiments with neutrons, the neutron flux and the neutron storage time in the measuring setup are of primary importance. These quantities can be increased by using a storage device for neutrons generated by a pulsed source. In a storage device with material walls, both parameters are determined by the probabilities of neutron absorption and diffuse scattering upon reflection from the storage walls, as well as by the neutron decay probability. This work considers a neutron measurement method and presents the results of an experimental determination of the probability of diffuse neutron scattering in a wave resonator.

When studying the interaction of neutrons with a force field, the important parameters are the neutron flux and the time the neutron stays in the measuring setup. To increase them, a neutron accumulator generated by a pulsed or continuously acting source can be used. Both parameters in a storage ring with material walls are determined by the probabilities of neutron capture by atomic nuclei and diffuse neutron scattering on the surface roughness of the walls. The task of definition of probabilities of neutron capture and scattering processes in the mirror reflection channel is considered. An imaginary potential of neutron interaction with the medium is introduced, which is responsible for the diffuse scattering of neutrons. Requirements for the wall roughness of the neutron storage ring are formulated.

The relationships for reflection and transmission amplitudes from a layered structure placed in a magnetic field are given. A calculation method whereby a vacuum gap is introduced between the magnetic field region and the structure has been used. We calculate neutron reflection and transmission factors and polarization for layered noncollinear and nonplanar structures placed in a magnetic field perpendicularly directed to the layers. The reflection of polarized neutrons from a magnetic layered structure of Al(10 nm)/Co(27.5 nm)/Al(140 nm)/Ni(27.5 nm)/Si, placed in a magnetic field perpendicular to the layers, has been experimentally determined. A conclusion about the occurrence of neutron polarization in the direction perpendicular to the magnetic moments of the layers has been made. This occurs due to the inequality of probabilities of neutron spin flip along and opposite the magnetic field direction.

A neutron gate is proposed for the accumulator with nonmagnetic walls. The gate is a part of the accumulator wall to which a magnetic field is applied during the neutron pulse as inflow of neutrons into the accumulator occurs. At this time, the gate operates based on the compensation of the nuclear potential of the neutron interaction by the magnetic potential. In intervals between neutron pulses, the probability of neutron absorption in the gate and in the entire accumulator is defined by the subbarrier reflection of neutrons from the accumulator wall, being as small as 10–5−10–4

We have shown the feasibility of detecting gamma quanta in a neutron experiment in the mode of resonantly enhanced standing waves (RESW) from a 1 nm thick gadolinium film placed in a resonator structure consisting of a 50 nm niobium layer on a sapphire substrate and coated with a 10 nm tantalum-copper film alloy. The mass of gadolinium used in the experiment was 2 μg, which is 25 times less than that in the experiment by H. Zhang et al. (H. Zhang et al., Phys. Rev. Lett. 72, 3044 (1994)). Quantitative calculations show that the experimental conditions make it possible to detect a gamma signal at waveguide resonance from a gadolinium sample weighing 40 nanograms. Thus, RESW gamma spectrometry is a powerful method for characterizing heterostructures with ultrathin gadolinium layers. In particular, it can be used to study the kinetics of interaction of hydrogen with nanometer films in which a thin layer of gadolinium is used as a label layer.

— The results of studying thin films and superlattices of rare-earth helimagnets Dy and Ho using a neutron reflectometer are presented. Neutron reflectometry is shown to allow the magnetic phase transitions in these nanostructures to be studied and information about the periodicity of magnetic helices in them to be collected. It is proposed to create a neutron reflectometer capable of conducting polarization analysis on the DARIA compact neutron source, optimized for studying long-period magnetic ordering in rare-earth helimagnets, and the possible directions of this optimization are indicated.

Different regimes of a neutron wave field are considered. The use of grazing neutron incidence geometry in the regime of standing waves with detection of specularly reflected neutrons and secondary radiation in the form of charged particles, gamma quanta, and scattered and spin-flip neutrons is substantiated. The new method of measurements implemented in the studies of layered structures combines the wave properties of neutron propagation and particle properties of neutrons in nuclear reactions. Some experimental data on the estimation of parameters for this method are given. The prospects in the development of neutron reflectometry and particle–wave measurements are pointed out.

The development of neutron reflectometry is currently associated, in particular, with the detection of secondary radiation emitted by atomic nuclei. In this regard, the problem of determining the probability of neutron absorption in a layered structure is very important. Various expressions are derived for the neutron-absorption coefficient. As an example, calculations are performed for a three-layer resonator structure.

The review presents the results of studies by neutrons of the magnetism phenomena in ferromagnetic-superconducting inhomogeneous structures carried out by the authors over fifteen years. The presence of superparamagnetic clusters, ferromagnetic domains, and superconducting vortices in real inhomogeneous layered structures leads to new magnetic phenomena. Reflectometry of polarized neutrons, being a powerful method for studying the spatial distribution of magnetization on a spatial scale from fractions of nanometers to tens of microns, makes it possible to study the whole spectrum of magnetic phenomena that occur in ferromagnetic-superconducting structures.

Determining the probability of the neutron–antineutron transformation has been the subject of research for five decades. To increase the luminosity in experiments to measure the probability of this process, it is proposed that a neutron guide be used as it increases the solid angle of neutron-source visibility. To increase the range of values of the wave vector of neutrons and antineutrons, it is proposed that a neutron guide with a supermirror coating be employed. In this work, we simulate a multilayer structure in which the range of wave-vector values is extended. The structure is a supermirror in which the layers consist of tungsten and barium isotopes.

The results of studying a superlattice of alternating layers of rare-earth helimagnets [Dy(6 nm)/Ho (6 nm)] × 34 by neutron reflectometry and X-ray diffraction are presented. It is shown that during the growth of helimagnetic structures on sapphire substrates with a Nb buffer layer by magnetron sputtering, the orientational relations $$\left( {1\bar {1}02} \right)$$ Al2O3||(110)Nb|| $$\left( {0001} \right)$$ (Dy/Ho) and the crystal lattices of Nb and the structure of rare-earth helimagnets are completely relaxed. It is also found that two different magnetic helicoids are formed in the sample, propagating coherently in Dy and Ho layers, respectively, with periods and Néel and Curie temperatures that differ from the characteristic temperatures of single crystals and thin one-component Dy and Ho films.

The role of size effects in the formation of the magnetic structure of Dy and Ho thin films in absence of epitaxial strain is studied in this work. It was found that, for Dy in the temperature range between the Néel temperature and the Curie temperature of bulk Dy and, for Ho, in the temperature range between the Néel temperature and the temperature of phase transition into the conic phase, the temperature dependences of the period of magnetic helicoid in the bulk and film metals are similar. The character of the transition into the ferromagnetic phase in the Dy films changes at lower temperatures, and the transition into the commensurable conic phase in the Ho films is suppressed. This is explained exclusively by the influence of dimensional effects.

In this paper, the results of investigating thin films of rare-earth helimagnetics (REMs) Dy and Ho by polarized neutron reflectometry are presented. It is shown that the growth by magnetron sputtering of rare-earth structures on sapphire substrates with a buffer layer Nb $$\left[ {1\bar {1}02} \right]$$ Al2O3||[110]Nb|| $$\left[ {0001} \right]R$$ leads to complete relaxation of the Nb crystal lattices and the rare-earth film. It is found that some magnetic phase transitions typical of bulk Dy and Ho are not observed in 200 nm [0001]R thin films or are observed in a modified form. Differences between the Néel and Curie temperatures of thin REM films compared to bulk REMs are determined based on polarized-neutron-reflectometry data and measurements of the temperature dependence of the magnetization in the sample plane.

The neutron reflectometry method is used to measure the spatial profile of the potential of interaction between neutrons and a medium. At the interface between media, the interaction potential is the sum of potentials of individual isotopes. Neutrons and gamma radiation emitted by the atomic nuclei of an element are recorded to determine the potential of interaction between neutrons and individual isotopes. Channels for the recording of gamma quanta and spin-flipped neutrons are created using a REMUR spectrometer. Channel testing results are given, model calculations of the neutron absorption coefficients are carried out, and prospects related to the recording of gamma quanta and polarized neutrons are discussed.

An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X21880013

Neutron reflectometry is a method for measuring the spatial profile of the neutron interaction potential with the medium. The interaction potential is the sum of neutron interaction potentials with separate isotopes of the medium. To determine the neutron interaction potential with the structure units, secondary radiation is simultaneously registered with neutrons. Channels for registering secondary radiation of charged particles, gamma rays and neutrons, having experienced spin flip, have been developed on the REMUR spectrometer of the IBR-2 reactor in Dubna (Russia). The necessity of registering secondary radiation in neutron reflectometry is justified, a method developed for measuring secondary radiation is described and the results of testing channels for registering secondary radiation on the REMUR spectrometer are presented in the paper.

We have used spin-polarized neutron reflectometry to investigate the magnetization profile of superlattices composed of ferromagnetic Gd and superconducting Nb layers. We have observed a partial suppression of ferromagnetic (F) order of Gd layers in [Gd(d(F))/Nb(25 nm)](12) superlattices below the superconducting (S) transition of the Nb layers. The amplitude of the suppression decreases with increasing d(F). By analyzing the neutron spin asymmetry we conclude that the observed effect has an electromagnetic origin-the proximity-coupled S layers screen out the external magnetic field and thus suppress the F response of the Gd layers inside the structure. Our investigation demonstrates the considerable influence of electromagnetic effects on the magnetic properties of S/F systems.

The heterogeneous ferromagnetic–superconducting layered heterostructures V/Fe0.7V0.3/V/Fe0.7V0.3/Nb and Nb/Ni0.65(0.81)Cu0.35(0.19), which contain magnetic clusters and ferromagnetic domains, are studied. The magnetic and superconducting properties of the structures depend on the magnetic-layer thickness, the magnetic field, and the time elapsed from structure preparation. We detected the interaction of clusters with a domain structure, diamagnetism and magnetization reversal of the magnetic layer during the superconducting transition in a ferromagnetic–superconducting heterostructure, and a superconducting transition in the magnetic layer. The magnetic and resistive properties of the heterostructures changed in several weeks and months.

An ionization chamber is installed to the REMUR neutron spectrometer, situated at channel no. 8 of the IBR-2. A layered structure containing a layer of the isotope under study with a thickness of several nanometers is placed into the chamber. A neutron beam enters the chamber and is incident on the structure. The reflected neutron beam and the neutron beam transmitted through the structure are recorded by a detector located outside the chamber. A fraction of neutrons incident on the structure is captured by the nuclei of the isotope under study. As a result, secondary radiation is generated in the form of charged particles, which are recorded by the ionization chamber. The dependences of the neutron and charged particle intensities on the transmitted wave vector of neutrons are used to determine the spatial dependences of the potential of interaction between neutrons with the entire structure and with a layer of the isotope under study. The neutron spectrometer in grazing geometry, using which the neutrons and charged particles are recorded in studying the layered structures, is described. The results of spectrometer testing with the use of structures containing the 6Li isotope are given.

We report on a study of the structural, magnetic, and superconducting properties of Nb(25 nm)/Gd(d(f))/Nb(25 nm) hybrid structures of a superconductor/ferromagnet (S/F) type. The structural characterization of the samples, including careful determination of the layer thickness, was performed using neutron and x-ray scattering with the aid of depth-sensitive mass spectrometry. The magnetization of the samples was determined by superconducting quantum interference device magnetometry and polarized neutron reflectometry, and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8 nm) layer was shown. The analysis of the neutron spin asymmetry allowed us to prove the absence of magnetically dead layers in junctions with Gd interlayer thickness larger than one monolayer. The measured dependence of the superconducting transition temperature T-c(d(f)) has a damped oscillatory behavior with well-defined positions of the minimum at d(f) = 3 nm and the following maximum at d(f) = 4 nm, in qualitative agreement with prior work [J. S. Jiang et al., Phys. Rev. B 54, 6119 (1996)]. We use a theoretical approach based on the Usadel equations to analyze the experimental Tc (df) dependence. The analysis shows that the observed minimum at d(f) = 3 nm can be described by the so-called zero to pi phase transitions of highly transparent S/F interfaces with a superconducting correlation length xi(f) approximate to 4 nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co, and Ni, thus simplifying the preparation of S/F structures with d(f) similar to xi(f) which are of topical interest in superconducting spintronics.