arXiv subjects

V. P. Timofeev

Publications and source records attributed to V. P. Timofeev.

14 recordsLinked to original sources

arXiv2026

High-Temperature Superconductivity of the Fe-Se-H compound

Using an EPR spectrometer, the dependences of microwave power absorption on magnetic field up to 6000 Oe were measured at temperatures of 3.6-25 K and 295 K in a powdered compound Fe-Se-H, obtained by thermal diffusion of hydrogen into a FeSe single crystal with a critical temperature of 8 K. The shape of the dependences and the analysis of the measurement results confirm the superconductivity of the Fe-Se-H compound at normal pressure, both at temperatures of 3.6-25 K and at 295 K, i.e., at room temperature.

cond-mat.supr-con↗

arXiv2026

Determination of the properties of a superconducting single crystal FeSe using an EPR spectroscopy

Using an EPR spectrometer, the properties of single-crystal FeSe were studied in a magnetic field up to 6000 Oe at temperatures from 3.5 K to 8 K in the superconducting state and at temperatures above 8K and up to 25K in the normal state. It was shown that by measuring non-resonant spectrometer signals in zero and weak magnetic fields up to 30 Oe, it is possible to determine critical temperature Tc, the superconducting transition width, and the value of the first critical magnetic field Hc1 in FeSe single-crystal. Resonant EPR signals are observed in fields at 1400 Oe and 3400 Oe, which corresponds to the paramagnetism of doubly ionized iron atoms (Fe2+) in the FeSe crystal. Non-resonant EPR signals in a magnetic field up to 6000 Oe at temperatures from 3.5K to 8K are a nonlinear function of the field, and correspond to the superconducting mixed state of the FeSe, but at temperatures above 8K (up to 25K) they are field independent.

cond-mat.supr-con↗

arXiv2024

Hydrogen in superconductors

Information is presented on the state of research on the effect of hydrogen on the superconducting properties of various compounds. The review consists of an introduction, one appendix and four sections: methods for the synthesis of modern hydrogen-containing superconductors, experimental studies of the properties of hydrogen-containing superconductors, on the mechanisms of the influence of hydrogen on superconductivity, problems and prospects of hydrogen-containing superconductors.

cond-mat.supr-con↗

arXiv2021

Enhancement of the pinning potential in a single-crystal superconductor FeTe0.65Se0.35 under the influence of hydrogen sorption

As a result of experimental studies of the single-crystal iron-chalcogenide compound FeTe0.65Se0.35, the effect of structural transitions caused by hydrogen sorption on the magnetic and current-carrying properties of a superconductor has been established. An increase in the volume-averaged effective pinning potential (and the associated critical current density) after the process of hydrogen sorption at temperatures up to 150 °C - 200 °C can be explained by the appearance of additional pinning centers due to the local action of implanted H ions on its crystal structure and electronic states. It was confirmed that hydrogenation is an efficient tool for increasing flux pining properties of superconductors.

cond-mat.supr-con↗

arXiv2017

Dynamics of trapped magnetic flux in superconducting FeTe0.65Se0.35

The magnetic moment in the superconducting and normal state of a crystalline FeTe0.65Se0.35 superconductor, grown by the Bridgman's method with relatively high growth rate, was measured. The temperature and magnetic field dependences of magnetization and its relaxation time were determined. Studied crystal, being non-uniform due to high growth rate of 5 mm/h, exhibits smaller width of superconducting transition in comparison with an ideal crystal grown with velocity of 1 mm/h, and the difference in magnetic properties of crystals grown with various growth rate, related to their microstructure, is discussed.

cond-mat.supr-con↗

arXiv2016

Microstructural and transport properties of superconducting FeTe0.65Se0.35 crystals

The issue concerning the nature and the role of microstructural inhomogeneities in iron chalcogenide superconducting crystals of FeTe0.65Se0.35 and their correlation with transport properties of this system was addressed. Presented data demonstrate that chemical disorder originating from the kinetics of the crystal growth process significantly influences the superconducting properties of an Fe-Te-Se system. Transport measurements of the transition temperature and critical current density performed for microscopic bridges allow us to deduce the local properties of a superconductor with microstructural inhomogeneities, and significant differences were noted. The variances observed in the local properties were explained as a consequence of weak superconducting links existing in the studied crystals. The results confirm that inhomogeneous spatial distribution of ions and small hexagonal symmetry nanoscale regions with nanoscale phase separation also seem to enhance the superconductivity in this system with respect to the values of the critical current density. Magnetic measurements confirm the conclusions drawn from the transport measurements.

cond-mat.supr-con↗

arXiv2015

Anisotropy of the magnetic properties of the FeTe0.65Se0.35 superconductor

The magnetization anisotropy of a layered superconductor FeTe0.65Se0.35 sample is experimentally studied in a magnetic field directed either along the layers of the plane, or perpendicular to them. The value of the vortex pinning potential in a weak magnetic field, and the critical current density ratio are determined for these directions. The results are discussed within the framework of presenting the sample as layers of fine single crystals, divided by weak interlayer superconducting bonds with magnetic inclusions.

cond-mat.supr-con↗

arXiv2014

Averaged effective pinning potential in YBCO single crystals close to Tc

In this paper we present our results on the low density magnetic flux pinning characteristics, obtained though HTSC samples magnetization relaxation measurements M(t) near the phase transition temperatures (0,8 < T/Tc > 0,99).As the main object of investigation we have chosen pure YBa2Cu3O7-x (YBCO) single crystal samples with optimal oxygen saturation. We note the presence of strong pinning in the system of unidirectional planar defects and a significant nonmonotonicity of the Up(T) dependence behavior for low density trapped magnetic flux.

cond-mat.supr-con↗

arXiv2013

Enhanced pinning in high-temperature superconducting cuprate single crystals at low DC magnetic field

Low density flux dynamics in Nd based cuprate (NdBa2Cu3O7-x) HTSC single crystals trapped in 1 Oe range DC magnetic fields were investigated for the first time. Complex measurements of time, temperature and field dependence of magnetization were performed. Using the results obtained and the Anderson-Kim model the normalized magnetization relaxation rate S and the averaged effective pinning potential U were calculated. We show a significant (one or even two orders) increase in the effective pinning potential in these samples in comparison with measurements performed in high magnetic fields for similar cuprate single crystals formerly. In a wide enough range of temperatures close to Tc (0.72 < T/Tc < 0.93) it has been shown that the doping of NdBa2Cu3O7-x single crystals with calcium atoms leads to the increase of the averaged effective pinning potential with an insignificant decreasing of the critical temperature.

cond-mat.supr-con↗

arXiv2012

Low density flux pinning in YBCO single crystals

The Abricosov vortex and bundles dynamics was experimentally investigated in Earth's magnetic field range. Isothermal relaxation features in YBCO single crystal samples with strong pinning centers were studied for different sample-field orientation. The normalized relaxation rate S obtained allowed to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results for similar measurements in significantly higher magnetic fields was performed. To compare different Jc measuring techniques magnetization loop M(H) measurements, were made. These measurements provide many important parameters of the sample under study (penetration field Hp, first critical field Hc1, etc.) that contain the geometrical configuration of the samples.

cond-mat.supr-con↗

arXiv2011

Nonlogarithmic magnetization relaxation in HTSC

An experimental study of low density captured magnetic flux dynamics in YBCO single crystal samples near the superconducting phase transition point has been performed. Vortex dynamics similar to thermally assisted flux flow regime (TAFF) has been observed for the first time in such weak fields. It will be shown that Zeldov's thermoactivated creep model successfully describes the behavior of the magnetization in the YBCO single crystals in our experiments. Within the framework of this model the estimation of normalized relaxation rate was made.

cond-mat.supr-con↗

arXiv2009

Trapped low magnetic field dynamics in YBCO single crystals

Trapped low magnetic flux dynamics including local ones are investigated in YBCO single crystals in the strong thermal fluctuations domain near the superconducting phase transition temperatures. The essential difference from quasi-logarithmic isothermal relaxation of a magnetization behavior (observed earlier in high magnetic fields) was established. Within the framework of classic model of a thermal activated vortices creep the estimation of an effective pinning potential was made at these temperatures.

cond-mat.supr-con↗

arXiv2005

Magnetic relaxation of superconducting YBCO samples in weak magnetic fields

For the first time, magnetization of high-Tc samples with different crystalline structure and its isothermal relaxation is studied at very weak constant fields (H <= 0.1 Oe) for temperatures close to the critical ones. Essential influence of twin boundaries in YBCO single crystals on magnetic relaxation rate is shown. An estimation of effective pinning potential is made in the framework of the collective pinning model.

cond-mat.supr-con↗

arXiv2004

Possible Josephson-like behavior of the YBa2Cu3O7-x single crystal twin boundaries in low magnetic fields

The experimental results on the magnetic response of YBCO single crystals with unidirectional twin boundary planes in low magnetic fields (0.01 - 1 Oe) are discussed. The observed non-monotone temperature dependence of magnetization is interpreted within a plausible model of a system of the Josephson weak links in the twin boundary planes and on the basis of the order parameter anisotropy.

cond-mat.supr-con↗