L. Tagirov | Kazan Federal University (original) (raw)

Papers by L. Tagirov

... Phys. 91, 8093 (2002). [7] A. Punnoose, MS Seehra, WK Park, and JS Moodera, J. Appl. Phys. 93... more ... Phys. 91, 8093 (2002). [7] A. Punnoose, MS Seehra, WK Park, and JS Moodera, J. Appl. Phys. 93, 7867 (2003). [8] BZ Rameev, F. Yıldız, LR Tagirov, B. Aktaş, WK Park, and JS Moodera, J. Magn. Magn. Mater. 258-259, 361 (2003). ...

Physical Review B, 1995

Sputtered Fe/Nb/Fe trilayers were prepared with Nb thicknesses d Nb in the range 300-800 Å and wi... more Sputtered Fe/Nb/Fe trilayers were prepared with Nb thicknesses d Nb in the range 300-800 Å and with Fe thicknesses d Fe in the range 0-30 Å. X-ray reflectivity measurements revealed the high quality of the film structure with low surface and interface roughnesses. Magnetic properties of the samples were studied using the magneto-optical Kerr effect, ferromagnetic-resonance and magnetization measurements by a SQUID magnetometer. For constant d Fe a decrease of T c with decreasing d Nb was observed up to a critical thickness d Nb crit below which superconductivity vanishes. We derived d Nb crit Ϸ320 Å independent of d Fe for d Fe у7 Å. The temperature dependence of the upper critical field H c2 (T) showed two-and three-dimensional features for parallel and perpendicular orientations of the magnetic field, respectively. At the Nb/Fe interface in the trilayer systems an Fe-rich interlayer with nonmagnetic Fe is formed with a thickness depending sensitively on the preparation conditions. We observed a nonmonotonic dependence of the superconducting transition temperature T c with increasing d Fe and a definite maximum in T c (d Fe ) at the onset of ferromagnetic order within the Fe layers. This maximum is attributed to a modification of the repulsive interaction between the electrons in the magnetically ''dead'' Fe-rich interlayer when an exchange field in the Fe layer is present.

Physical Review B, 2010

We study the superconducting properties of a series of Fe/V/Fe trilayers with variable thickness ... more We study the superconducting properties of a series of Fe/V/Fe trilayers with variable thickness of the Fe layer and constant thickness of the V layer. For an optimized combination of thicknesses and structural quality of the thin films we observe a re-entrant behavior of the superconducting state when plotting the superconducting transition temperature T c as a function of the Fe thickness d Fe . With increasing d Fe , T c drops sharply up to d Fe Ӎ8 Å, then the superconductivity disappears, and it restores again at d Fe у12 Å.

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 d Fe fixed and varying the thickness of the Cr-layers d Cr , the superconducting transition temperature T c first rises reaching a maximum at d Cr = 40 Å and then sharply drops for larger Cr-thickness. Keeping d Cr constant and varying d Fe the superconducting transition temperature becomes independent on d Fe for d Cr Ͼ 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 d Cr Ͻ 40 Å and undergoes a transition to an incommensurate spin density wave state for d Cr Ͼ 40 Å.

Physical Review B, 2013

The theory of superconductor-ferromagnet (S-F) heterostructures with two ferromagnetic layers pre... more The theory of superconductor-ferromagnet (S-F) heterostructures with two ferromagnetic layers predicts the generation of a long-range, odd-in-frequency triplet pairing at non-collinear alignment (NCA) of the magnetizations of the F-layers. This triplet pairing has been detected in a Nb/Cu 41 Ni 59 /nc-Nb/Co/CoO x spin-valve type proximity effect heterostructure, in which a very thin Nb film between the F-layers serves as a normal conducting (nc) spacer. The resistance of the sample as a function of an external magnetic field shows that for not too high fields the system is superconducting at a collinear alignment of the Cu 41 Ni 59 and Co layer magnetic moments, but switches to the normal conducting state at a NCA configuration. This indicates that the superconducting transition temperature T c for NCA is lower than the fixed measuring temperature. The existence of a minimum T c , at the NCA regime below that one for parallel or antiparallel alignments of the F-layer magnetic moments, is consistent with the theoretical prediction of a singlet superconductivity suppression by the long-range triplet pairing generation.

physica status solidi (c), 2004

Journal of Physics: Conference Series, 2012

ABSTRACT Interference effects of the superconducting pairing wave function in thin film bilayers ... more ABSTRACT Interference effects of the superconducting pairing wave function in thin film bilayers of Nb as a superconductor (S) and Cu41Ni59 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.

Journal of Magnetism and Magnetic Materials, 2006

Magnetic properties of granular (Co 40 Fe 40 B 20 ) x (SiO 2 ) 1Àx thin films (x ¼ 0:37 À 0:53) h... more Magnetic properties of granular (Co 40 Fe 40 B 20 ) x (SiO 2 ) 1Àx thin films (x ¼ 0:37 À 0:53) have been studied by ferromagnetic resonance (FMR) technique. Samples have been prepared by ion-beam deposition of Co-Fe-B particles and SiO 2 on sitall ceramic substrate. The FMR measurements have been done for different orientations of DC magnetic field with respect to the sample plane. It was found that the deduced value of effective magnetization from FMR data of the thin granular film is reduced by the volume-filling factor of the bulk saturation magnetization. The overall magnetization changes from 152 to 515 G depending on the ratio of the magnetic nanoparticles in the SiO 2 matrix. From angular measurements an induced in-plane uniaxial anisotropy has been obtained due to the preparation of the film conditions as well. r

physica status solidi (a), 2006

Thin films of various half-metallic ferromagnets, such as chromium dioxide (CrO 2 ) and Heusler a... more Thin films of various half-metallic ferromagnets, such as chromium dioxide (CrO 2 ) and Heusler alloys (Co 2 Cr 0.6 Fe 0.4 Al, Co 2 MnSi) have been investigated by ferromagnetic resonance (FMR) technique. It is demonstrated that FMR is a very efficient method to study the nanoscale magnetic properties, in particular to probe the magnetic anisotropy and magnetic inhomogeneities of ferromagnetic thin films. Epitaxial CrO 2 thin films of various thicknesses (25 -535 nm) have been deposited on TiO 2 (100) substrates by chemical vapor deposition process. It is shown that the magnetic behavior of the CrO 2 films results from a competition between the magnetocrystalline and strain anisotropies. For the ultrathin CrO 2 film (25 nm) the magnetic easy axis switches from the c-direction to the b-direction of the rutile structure. Thin-film Co 2 Cr 0.6 Fe 0.4 Al samples (25 nm or 100 nm) have been grown by DC magnetron sputtering either on unbuffered SiO 2 (100) substrates or on the substrates capped by a 50 nm thick V buffer layer. The effects of the vanadium buffer layer and of the film thickness are revealed by FMR studies of the Co 2 Cr 0.6 Fe 0.4 Al samples. Well-resolved multiple spin-wave modes are observed in the unbuffered Co 2 Cr 0.6 Fe 0.4 Al sample with a thickness of 100 nm and the exchange stiffness constant has been estimated. Thin films of Co 2 MnSi (4 -100 nm) have been grown by DC sputtering on silicon substrates on top of a 42 nm thick V seed layer and capped either by Al 2 O 3 or by Co and V layers. A set of the 80 nm thick films has been annealed at different temperatures in the range of 425 -550 °C. FMR studies of the Co 2 MnSi samples shows that at the fixed annealing temperature (450 °C) the highest magnetization is observed in the sample with a thickness of 61 nm, while the thicker samples (100 nm) reveal not only a lower magnetization but greater magnetic inhomogeneity as well. An annealing treatment at T ≥ 450 °C is essential to obtain higher magnetization as well as uniform magnetic properties in the Co 2 MnSi films. Weak SWR modes have also been observed in the thick Heusler films.