arXiv subjects

V. L. Aksenov

Publications and source records attributed to V. L. Aksenov.

12 recordsLinked to original sources

arXiv2021

Neutron reflectometry with registration of secondary radiation

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.

cond-mat.mtrl-sci↗

arXiv2019

Reflectometry with registration of secondary radiation at total neutron reflection

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

cond-mat.mtrl-sci↗

arXiv2019

Magnetic proximity effect in [Nb/Gd] superlattices seen by neutron scattering

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.

cond-mat.supr-con↗

arXiv2018

Magnetic and Superconducting Phase Diagram of Nb/Gd/Nb trilayers

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 "$π$" phase transition of highly transparent S/F interfaces with the superconducting correlation length $ξ_f \approx 4$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 $d_f \sim ξ_f$ which are of topical interest in superconducting spintronics.

cond-mat.supr-con↗

arXiv2013

On the feasibility to study inverse proximity effect in a single S/F bilayer by Polarized Neutron Reflectometry

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.

cond-mat.str-el↗

arXiv2010

Magnetic proximity effects in V/Fe superconductor/ferromagnet single bilayer revealed by waveguide-enhanced polarized neutron reflectometry

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.

cond-mat.supr-con↗

arXiv2010

Feasibility of study magnetic proximity effects in bilayer "superconductor/ferromagnet" using waveguide-enhanced Polarized Neutron Reflectometry

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.

cond-mat.supr-con↗

arXiv2009

Study of proximity effects in superconductor/ferromagnet interface using waveguide enhancement of neutron standing waves

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.

cond-mat.supr-con↗

arXiv2008

Optimization of parameters of nanostructure for study inverse proximity effects on "superconductor-ferromagnetic" interface using Polarized Neutron Reflectometry in enhanced standing wave regime

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.

cond-mat.supr-con↗

arXiv2007

Evidence for nonmonotonic magnetic field penetration in a type-I superconductor

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.

cond-mat.supr-con↗

arXiv2001

Model of separated form factors for unilamellar vesicles

New model of separated form factors is proposed for the evaluation of small-angle neutron scattering curves from large unilamellar vesicles. The validity of the model was checked by comparison to the model of hollow sphere. The model of separated form factors and hollow sphere model give reasonable agreement in the evaluation of vesicle parameters.

physics.bio-ph↗

arXiv1997

Electron-Phonon Interaction and Raman Linewidth in Superconducting Fullerides

We propose a microscopic theory of interaction of long wave molecular phonons with electrons in fullerides in the presence of disorder. Phonon relaxation rate and frequency renormalization are discussed. Finite electronic bandwidth reduces phonon relaxation rate at $q=0$. Electron-phonon coupling constants with molecular modes in fullerides are estimated. The results are in good agreement with photoemission experiments.

cond-mat.supr-con↗