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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.

Neutron reflectometry is a method for measuring of the spatial dependence (profile) of the potential interaction between neutron and medium. At interface of media the interaction potential is the sum of the elements potentials. For definition of potentials of separate elements (isotopes) a secondary radiation is recorded. Recording channels of secondary radiation are created on spectrometer REMUR at pulsed reactor IBR-2 in Dubna (Russia). The results for testing of the channels are reported and perspectives of reflectometry with registration of secondary radiation are discussed

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(25nm)]$_{12}$ 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.

We report on a study of the structural, magnetic and superconducting properties of Nb(25nm)/Gd($d_f$)/Nb(25nm) 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 SQUID magnetometry and polarized neutron reflectometry and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8nm) 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 $d_f$=3nm and the following maximum at $d_f$=4nm; the behavior, which is in qualitative agreement with the prior work (J.S. Jiang et al, PRB 54, 6119). The analysis of the $T_c(d_f)$ dependence based on Usadel equations showed that the observed minimum at $d_f$=3nm can be described by the so called "$0$" to "$\pi$" phase transition of highly transparent S/F interfaces with the superconducting correlation length $\xi_f \approx 4$nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures with $d_f \sim \xi_f$ which are of topical interest in superconducting spintronics.

Peculiarities of the formation of a neutron enhanced standing wave in the structure with a thin highly absorbing layer of gadolinium are considered in the article. An analogue of the poisoning effect well known in reactor physics was found. The effect is stronger for the Nb/Gd/Nb system. Despite of this effect, for a Nb/Gd bilayer and a Nb/Gd/Nb trilayer placed between Al2O3 substrate and Cu layer, it is shown theoretically and experimentally that one order of magnitude enhancement of neutron density is possible in the vicinity of the Gd layer. This enhancement makes it possible to study domain formation in the Gd layer under transition of the Nb layer(s) into the superconducting state (cryptoferromagnetic phase)., Comment: 5 pages, 2 figures

We report on observation of the time reversal symmetry breaking in unpolarized neutrons scattering experiment. Neutron transmittivity through the system consisting of two magnetic mirrors placed in an external magnetic field is measured. Time reversal symmetry holds for coplanar magnetic configuration, meaning that transmitted intensity does not change when interchanging neutron source and detector. Contrarily, for noncoplanar magnetic configuration the time reversal symmetry breaks down. In this case the transmitted intensity changes when interchanging the source and detector. The observed time reversal symmetry breaking is the consequence of the one of the most fundamental properties of quantum mechanics, namely the non-commutativity of spin algebra.

Here we report on a feasibility study aiming to explore the potential of Polarized Neutron Reflectometry (PNR) for detecting the inverse proximity effect in a single superconducting/ferromagnetic bilayer. Experiments, conducted on the V(40nm)/Fe(1nm) S/F bilayer, have shown that experimental spin asymmetry measured at T = 0.5TC is shifted towards higher Q values compared to the curve measured at T = 1.5TC. Such a shift can be described by the appearance in superconducting vanadium of magnetic sub-layer with thickness of 7 nm and magnetization of +0.8 kG., Comment: Changes in the 2nd version: small mistypes are corrected. Manuscript submitted to JETP let. 4 pages, 2 figures

The expressions are received for neutron reflection from the wave resonator placed in an oscillating magnetic field. The conditions are defined for optimal values of the neutron wave resonator and magnetic field parameters. Numerical calculations which support theory conclusions are carried out for real systems.

Polarized neutron reflectometry is used to study the magnetic proximity effect in a superconductor/ferromagnet (SC/FM) system of composition Cu(32nm)/V(40nm)/Fe(1nm)/MgO. In contrast to previous studies, here a single SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary signal enhancement is achieved by waveguide resonance, i.e. preparing the V(40nm)/Fe(1nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate and Cu top layer, respectively . A new magnetic state of the system was observed at temperatures below 0.7 TC. manifested in a systematic change in the height and width of the waveguide resonance peak. Upon increasing the temperature from 0.7 TC to TC, a gradual decay of this state is observed, accompanied by a 5% growth of the diffuse scattering. According to theoretical studies, such behavior is the result of the magnetic proximity effect. Due to the presence of the thin FM layer the superconducting electrons are polarized and, as a result, near the SC/FM interface an additional magnetic layer appears in the SC with thickness comparable to ksi, the coherence length of the superconductor., Comment: Submitted to the Journal of Superconductivity and Novel Magnetism. 11 pages, 6 figures.

A resonant enhancement of the neutron standing waves is proposed to use in order to increase the magnetic neutron scattering from a "superconductor/ferromagnet"(S/F) bilayer. The model calculations show that usage of this effect allows to increase the magnetic scattering intensity by factor of hundreds. Aspects related to the growth procedure (order of deposition, roughness of the layers etc) as well as experimental conditions (resolution, polarization of the neutron beam, background etc) are also discussed. Collected experimental data for the S/F heterostructure Cu(32nm)/V(40nm)/Fe(1nm)/MgO confirmed the presence of a resonant 60-fold amplification of the magnetic scattering., Comment: The manuscript of the article submitted to Crysstalography Reports. 23 pages, 5 figures

Equations for the neutron reflection amplitude from a magnetic non-collinear wave resonator (NWR) are obtained. It is shown that resonances of the same reflection order of neutrons experiencing spin-flip (spin-flip neutrons) appear in pairs. Conditions under which in the resonator square enhancement of the spin-flip neutron reflection intensity with respect to growth of the portion of scattered and absorbed neutrons takes place, are determined., Comment: Submitted to the journal "Nuclear Instruments and Methods in Physics Research Section A". Variant 2 is after referee's revision. Corresponding author is Yu.V. Nikitenko (nikiten@nf.jinr.ru). The manuscript contains 11 pages, 7 figures and 1 table. Keywords: Polarized neutron reflectometry; Layered structures; Neutron resonances

It is shown that transmission amplitudes of magnetic systems with noncollinear magnetization contain T-odd correlations. Relation of these T-odd correlations to T-invariance and detailed balance is discussed., Comment: 13 pages, 5 figures, presented at the conference ISINN17 Added acknowledgements

This work is devoted to experimental study of influence of superconductivity (S) on ferromagnetism (FM) (inverse proximity effects) with the help of Polarized Neutron Reflectivity. Combining meausurements of specular and diffuse intensities it is possible to obtain full picture of magnetization change in S/FM layered systems like magnetization rotation, domain state formation, inducing of magnetization in S layer, etc. To increase weak magnetic signal we propose to use enhanced neutron standing wave regime (e.g. waveguides). In previous work we have made calculation to increase enhcanced factor. Here we present results of preparation sets of S/FM samples and attestation of their structural, magnetic, superconducting and neutron waveguide properties., Comment: This work was presented on workshop 3-7 dec 2008, http://hungary.jinr.ru. Contains 4 pages and 3 figures

This work is devoted to experimental study of influence of superconductivity (S) on ferromagnetism (FM) (inverse proximity effects) with the help of Polarized Neutron Reflectivity. Combining meausurements of specular and diffuse intensities it is possible to obtain full picture of magnetization change in S/FM layered systems like magnetization rotation, domain state formation, inducing of magnetization in S layer, etc. To increase weak magnetic signal we propose to use enhanced neutron standing wave regime (e.g. waveguides). Choose of materials, optimization of thicknesses of layers, estimation of roughnesses influence is presented in this work., Comment: 7 pages, 5 figures

Polarized neutron reflectometry (PNR) provides evidence that nonlocal electrodynamics governs the magnetic field penetration in an extreme low-k superconductor. The sample is an indium film with a large elastic mean free path (11 mkm) deposited on a silicon oxide wafer. It is shown that PNR can resolve the difference between the reflected neutron spin asymmetries predicted by the local and nonlocal theories of superconductivity. The experimental data support the nonlocal theory, which predicts a nonmonotonic decay of the magnetic field., Comment: 5 pages, 4 figures, LaTex, corrected typos and figures