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Lenar Tagirov

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Papers by Lenar Tagirov

The role of additional layer N or S2 in superconducting triplet spin-valve S1/F1/N(S2)/F2

S VO LU M E I I M ON DA Y September 08–13, 2019, Ekaterinburg, Russia VII Euro-Asian Symposium «T... more S VO LU M E I I M ON DA Y September 08–13, 2019, Ekaterinburg, Russia VII Euro-Asian Symposium «Trends in MAGnetism» M.N. Miheev Institute of Metal Physics UB RAS Euro -A si an S ym p o si um « Tr en ds in M agn etism »: EASTM AG 2019 Ekaterin burg, Russ ia, Se pt em b er 0 813 , 2 01 9 BOOK OF ABSTRACTS. VOLUME II I.P 11 THE ROLE OF ADDITIONAL LAYER N OR S2 IN SUPERCONDUCTING TRIPLET SPIN-VALVE S1/F1/N(S2)/F2 R.R. Gaifullin1*, V.N. Kushnir2,3, R.G. Deminov1, L.R. Tagirov1,4, M.Yu. Kupriyanov1,5,6 and A.A. Golubov6,7 1Institute of Physics, Kazan Federal University, Kazan, Russia 2Belarus State University of Informatics and Radioelectronics, Minsk, Belarus 3Theoretical Physics Department, Belarusian State University, Minsk, Belarus 4Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center of RAS, Kazan, Russia 5Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia 6Moscow Institute of Physics and Technology, Dolgoprudny, Russia 7Faculty of Science...

Formation of Pores in Thin Germanium Films under Implantation by Ge+ Ions

Technical Physics Letters, 2020

Results are presented of a study of the morphology of germanium films nanostructured by ion impla... more Results are presented of a study of the morphology of germanium films nanostructured by ion implantation. Film samples were grown by magnetron sputtering in an ultrahigh-vacuum installation and then irradiated with 40 keV Ge + ions at fluences in the range of (1.8-8) × 10 16 ions/cm 2 . Scanning electron microscopy demonstrated that vacancy complexes with diameters of ~50-150 nm are gradually formed in the bulk of implanted germanium with increasing implantation fluence. After a certain implantation fluence is reached, the complexes emerge on the surface, thereby forming a developed surface profile of the irradiated films.

Professor Boris Zalmanovich Malkin

Magnetic resonance in solids, 2019

KFU) * "Magnetic Resonance in Solids. Electronic Journal" (MRSej) is a peer-reviewed, all electro... more

Professor Kochelaev, Boris Ivanovich

Magnetic resonance in solids, 2019

Electrical properties of titanium nitride films synthesized by reactive magnetron sputtering

Journal of Physics: Conference Series, 2017

Reactive dc magnetron sputtering was employed to produce thin films of titanium nitride using tit... more Reactive dc magnetron sputtering was employed to produce thin films of titanium nitride using titanium metallic target, argon as the plasma gas and nitrogen as the reactive gas. A set of the films was studied deposited on the Si, fused silica and crystalline (001) MgO substrates with various deposition conditions. The films deposited on the Si and SiO 2 substrates are polycrystalline while deposited at slow rate to the heated to 600C MgO substrate are highly epitaxial according both to XRD and LEED data. Electrical resistivity of the films was measured by means of the four-probe van der Pauw method.

Effect of irradiation by argon ions on hydrogen transport through the surface oxide layer of zirconium

Journal of Physics: Conference Series, 2016

Effect of zirconium irradiation by 1 keV Ar + ions on hydrogen transport through the surface oxid... more Effect of zirconium irradiation by 1 keV Ar + ions on hydrogen transport through the surface oxide layer is studied. It is shown that deuterium trapping under subsequent irradiation of the Ar-treated sample by deuterium atoms of thermal energies in D 2 + 30at.% O 2 gas mixture is 2 times less than trapping in the untreated sample. Besides, irradiation of the untreated sample by D-atoms provokes desorption of ≈25% of hydrogen contained therein, whereas hydrogen desorption from the ion-treated zirconium surface does not occur. It is proposed that oxygen depletion of the surface oxide layer, caused by ion bombardment, is a reason of mitigation of the hydrogen transport through this layer in both directions.

Vibrational properties and lattice specific heat of RbFeS2

AIP Conference Proceedings, 2018

Magnetic properties of chain antiferromagnets RbFeSe2, TlFeSe2, and TlFeS2

Bulletin of the Russian Academy of Sciences: Physics, 2017

Abstract⎯Single crystals of ternary ion chalcogenides RbFeSe 2 , TlFeSe 2 , and TlFeS 2 are studi... more Abstract⎯Single crystals of ternary ion chalcogenides RbFeSe 2 , TlFeSe 2 , and TlFeS 2 are studied by X-ray diffraction, SQUID magnetometry, and Mössbauer spectroscopy. Common structural units of these chalcogenides are tetrahedra of FeCh 4 (chalcogen Ch = Se, S), arranged in chains by sharing an edge. It is found that RbFeSe 2 , TlFeSe 2 , and TlFeS 2 undergo transition to a collinear antiferromagnetic state below temperatures T N = 248, 290, and 196 K, respectively. Their magnetic moments are oriented perpendicular to the axes of the chains of FeCh 4 tetrahedra.

Influence of the FFLO-like state on the upper critical field of a superconductor/ferromagnet bilayer: Angular and temperature dependence

Physical Review B, 2016

We investigated the upper critical magnetic field, Hc, of a superconductor-ferromagnet (S/F) bila... more We investigated the upper critical magnetic field, Hc, of a superconductor-ferromagnet (S/F) bilayer of Nb/Cu41Ni59 and a Nb film (as reference). We obtained the dependence of H c⊥ and H c (perpendicular and parallel to the film plane, respectively) on the temperature, T , by measurements of the resistive transitions and the dependence on the inclination angle, θ, of the applied field to the film plane, by non-resonant microwave absorption. Over a wide range, H c⊥ and H c show the temperature dependence predicted by the Ginzburg-Landau theory. At low temperatures and close to the critical temperature deviations are observed. While Hc(θ) of the Nb film follows the Tinkham prediction for thin superconducting films, the Nb/Cu41Ni59-bilayer data exhibit deviations when θ approaches zero. We attribute this finding to the additional anisotropy induced by the quasi-onedimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like state and propose a new vortex structure in S/F bilayers, adopting the segmentation approach from high-temperature superconductors.

Specific features of depth distribution profiles of implanted cobalt ions in rutile TiO2

Physics of the Solid State, 2011

This paper reports on the results of the calculation of the depth distribution profiles of the co... more This paper reports on the results of the calculation of the depth distribution profiles of the con centration of the impurity implanted into an anisotropic crystalline material. The sputtering of the irradiated material, fast one dimensional diffusion of the impurity along structural channels, and accumulation of the implanted impurity at different depths have been taken into account. The results of the calculations have been compared with the experimental distribution profiles of cobalt ions implanted into the crystal structure of rutile TiO 2 along and across structural channels at different temperatures of the irradiated substrate. A com parison of the model and experimental profiles has made it possible to evaluate the precipitation rate of cobalt in the TiO 2 matrix on different precipitation centers. A model has been proposed for explaining the unusual shift in the peak of the concentration distribution of implanted ions deep into the sample with an increase in the temperature of the irradiated substrate. The model has allowed one to separate the contributions from dif ferent phases of the impurity (nanoparticles and solid solution) to the magnetism of the Co : TiO 2 system.

Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

Physical Review B, 2010

We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state established due to the proximit... more We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state established due to the proximity effect in superconducting Nb/Cu 41 Ni 59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device (SQUID) magnetometry. These studies yield precise information about the thickness, and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu 41 Ni 59 layer thickness, T c (d S ) and T c (d F ), were investigated for constant thickness d F of the magnetic alloy layer and d S of the superconducting layer, respectively. All types of non-monotonic behaviors of T c versus d F predicted by the theory could be realized experimentally: from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, T c (d F ) diagrams of a hypothetical F/S/F spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results.

Superconducting∕ferromagnetic proximity effect mediated byCrspacer layers

Physical Review B, 2004

We have studied the superconducting proximity effect in the thin film system Fe/Cr/V/Cr/Fe where ... more We have studied the superconducting proximity effect in the thin film system Fe/Cr/V/Cr/Fe where the Cr layers play the role of screening layers between the superconducting V-layer and the strongly pair breaking Fe-layers. When keeping the thickness of the Fe-layers dFe fixed and varying the thickness of the Cr-layers dCr, the superconducting transition temperature Tc first rises reaching a maximum at dCr=40 Å and then sharply drops for larger Cr-thickness. Keeping dCr constant and varying dFe the superconducting transition temperature becomes independent on dFe for dCr>40 Å. The results demonstrate that the Cooper pairs penetrate into the Cr-layer to a depth of about 40 Å. From our experimental results we suggest that the Cr-layer is nonmagnetic for dCr<40 Å and undergoes a transition to an incommensurate spin density wave state for dCr>40 Å.

A Spin Valve Core Structure based on the Fulde-Ferrell Larkin-Ovchinnikov Like State: Studies on Bilayers and Trilayers of Superconductors and Ferromagnets

Journal of Physics: Conference Series, 2012

Interference effects of the superconducting pairing wave function in thin film bilayers of Nb as ... more Interference effects of the superconducting pairing wave function in thin film bilayers of Nb as a superconductor (S) and Cu 41 Ni 59 as ferromagnetic (F) material lead to critical temperature oscillations and reentrant superconductivity for increasing F-layer thickness. The phenomenon is generated by the Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state establishing in these geometries. So far detailed investigations were performed on S/F bilayers. Recently, we could also realize the phenomena in F/S bilayers where the S-metal now is grown on top of the F-material. Combining both building blocks yields an F/S/F trilayer, representing the core structure of the superconducting spin valve. Also for this geometry we observed deep critical temperature oscillations and reentrant superconductivity, which is the basis to obtain a large spin switching effect, i.e. a large shift in the critical temperature, if the relative orientation of the magnetizations of the F-layers is changed from parallel to antiparallel.

Anisotropic ferromagnetism in Co-implanted TiO2 rutile

Journal of Magnetism and Magnetic Materials, 2006

We have studied the magnetic properties of the Co-implanted TiO2 thin films by magneto-optical Ke... more

FMR studies of magnetic properties of Co and Fe thin films on Al2O3 and MgO substrates

Journal of Applied Physics, 1994

The effect of substrates on the magnetic properties has been studied for Co and Fe films both on ... more The effect of substrates on the magnetic properties has been studied for Co and Fe films both on Al2O3 (112̄0) and MgO (001) substrates by using ferromagnetic resonance techniques. For Fe(001)/MgO(001) samples the thickness dependence of the magnetocrystalline constant and of the effective magnetization values have been determined from the in-plane angular variation of the resonance field H0. Different reasons for the thickness dependencies of these parameters are discussed. For Co(111)/Al2O3(112̄0) the angular variation of H0 exhibits an uniaxial anisotropy, for which several causes are discussed. For Co(112̄0)/MgO(100) a four-fold in-plane anisotropy was observed which is due to the twinned structure of these samples.

Superconducting and magnetic properties of epitaxial high-quality Fe/Nb bilayers

Journal of Applied Physics, 1997

Single crystal Fe/Nb (110) bilayers with an Nb thickness dNb in the range from 140 to 650 Å and w... more Single crystal Fe/Nb (110) bilayers with an Nb thickness dNb in the range from 140 to 650 Å and with an Fe thickness dFe in the range from 5 to 100 Å were prepared using molecular beam epitaxy (MBE) techniques. For dFe⩾20 Å a decrease of the superconducting transition temperature Tc with decreasing dNb was observed. For dFe=20 Å the FMR data revealed a decrease of the effective magnetization of the Fe layer below the superconducting transition. This magnetization behavior is attributed to a spatial modulation of ferromagnetic order due to a modification of the RKKY interaction in the superconducting state.

Reentrant superconductivity and superconducting critical temperature oscillations in F/S/F trilayers of Cu41Ni59/Nb/Cu41Ni59 grown on cobalt oxide

Journal of Applied Physics, 2013

Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core of a superconducting... more Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core of a superconducting spin valve. The switching effect of the spin valve is based on interference phenomena occurring due to the proximity effect at the S/F interfaces. A remarkable effect is only expected if the core structure exhibits strong critical temperature oscillations, or most favorable, reentrant superconductivity, when the thickness of the ferromagnetic layer is increased. The core structure has to be grown on an antiferromagnetic oxide layer (or such layer to be placed on top) to pin by exchange bias the magnetization-orientation of one of the ferromagnetic layers. In the present paper, we demonstrate that this is possible, keeping the superconducting behavior of the core structure undisturbed.

Critical temperature oscillations and reentrant superconductivity due to the FFLO like state in F/S/F trilayers

Annalen der Physik, 2011

Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers, in which the establishing of a Fulde‐Fe... more Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers, in which the establishing of a Fulde‐Ferrell Larkin‐Ovchinnikov (FFLO) like state leads to interference effects of the superconducting pairing wave function, form the core of the superconducting spin valve. The realization of strong critical temperature oscillations in such trilayers, as a function of the ferromagnetic layer thicknesses or, even more efficient, reentrant superconductivity, are the key condition to obtain a large spin valve effect, i.e. a large shift in the critical temperature. Both phenomena have been realized experimentally in the Cu41Ni59/Nb/Cu41Ni59 trilayers investigated in the present work.

Reentrant Superconductivity inNb/Cu1−xNixBilayers

Physical Review Letters, 2006

We report on the first observation of a pronounced re-entrant superconductivity phenomenon in sup... more We report on the first observation of a pronounced re-entrant superconductivity phenomenon in superconductor/ferromagnetic layered systems. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu1-xNix. The superconducting transition temperature Tc drops sharply with increasing thickness dCuNi of the ferromagnetic layer, until complete suppression of superconductivity is observed at dCuNi ≈4 nm. Increasing the Cu1-xNix layer thickness further, superconductivity reappears at dCuNi≈13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.

Proximity effects in superconducting triplet spin-valve F2/F1/S

Journal of Magnetism and Magnetic Materials, 2015

We investigate the critical temperature T c of F2/F1/S trilayers (Fi is a ferromagnetic metal and... more We investigate the critical temperature T c of F2/F1/S trilayers (Fi is a ferromagnetic metal and S is a singlet superconductor), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. In this paper we demonstrate a possibility of the spin-valve effect mode selection (standard switching effect, the triplet spin-valve effect or reentrant T c ðαÞ dependence) by the variation of the F2/F1 interface transparency.