11 research outputs found
Unusual Behavior of Antiferromagnetic Superconductors in Low Magnetic Fields
In this article, we examine the superconducting properties of low- and
high- magnetic superconductors in magnetic fields close to the first
penetration field. Attention is paid to the properties that relate to the
interactions between antiferromagnetism and superconductivity. It is suggested
that several features characterizing the interplay between magnetic and
superconducting subsystems in low- superconductors can also be present in
high- materials, however, they have not been observed for any
non-substituted antiferromagnetic superconductors of the Y123 type. For the
GdBaCuO compound, a peak in the temperature
dependence of the ac susceptibility has been found for near the
N\'{e}el temperature of the Gd sublattice. This peak is attributed to the
suppression of superconducting persistent currents due to the pair breaking
effect that results from the enhanced magnetic fluctuations in the vicinity of
the phase transition temperature. This observation indicates that the
interaction between magnetic and conducting electrons is present for the
composition with , where magnetism is enhanced and superconductivity
diminished.Comment: To be published in Physica C; 14 pages, 7 figure
The magnetic and electric measurements of the multiferroic PbFe1/2Nb1/2O3 ceramics obtained using hot uniaxial pressure method
We present the results of investigations of Pb(Fe1/2Nb1/2)O3 (PFN) ceramic samples obtained using two-step synthesis (i.e. columbite method). For obtained samples complex investigations of microstructure, magnetic and electrophysical properties have been performed at low and at high temperatures. Microstructure is characterized by small grains with high homogeneity and high density (low porosity). Impedance of samples and the phase shift angle have been measured using LCR Meter. Next the AC electric conductivity, dielectric permittivity and loss tangent have been calculated. AC conductivity at frequency 3 Hz was measured in
similar way using Quantum Design PPMS System in magnetic fields 1000 Oe and 10000 Oe. At temperature range 240K-260K the anomalies of conductivity are observed. These anomalies depend on measuring cycle (heating, cooling) and magnetic field.[1] K. Uchino, J.R. Giniewicz, Micromechatronics, 2003 Marcel Dekker, New York.
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Structural and Superconducting Properties of RbOs2O6 Single Crystals
Single crystals of RbOs2O6 have been grown from Rb2O and Os in sealed quartz
ampoules. The crystal structure has been identified at room temperature as
cubic with the lattice constant a = 10.1242(12) A. The anisotropy of the
tetrahedral and octahedral networks is lower and the displacement parameters of
alkali metal atoms are smaller than for KOs2O6, so the "rattling" of the alkali
atoms in RbOs2O6 is less pronounced. Superconducting properties of RbOs2O6 in
the mixed state have been well described within the London approach and the
Ginzburg-Landau parameter kappa(0) = 31 has been derived from the reversible
magnetization. This parameter is field dependent and changes at low
temperatures from kappa = 22 (low fields) to kappa = 31 at H_{c2}. The
thermodynamic critical field H_{c}(0) = 1.3 kOe and the superconducting gap
2delta/k_{B}T_{c} = 3.2 have been estimated. These results together with
slightly different H_{c2}(T) dependence obtained for crystals and
polycrystalline RbOs2O6 proof evidently that this compound is a weak-coupling
BCS-type superconductor close to the dirty limit.Comment: 20 pages, 8 figures, 3 table
High magnetic field scales and critical currents in SmFeAs(O,F) crystals: promising for applications
Superconducting technology provides most sensitive field detectors, promising
implementations of qubits and high field magnets for medical imaging and for
most powerful particle accelerators. Thus, with the discovery of new
superconducting materials, such as the iron pnictides, exploring their
potential for applications is one of the foremost tasks. Even if the critical
temperature Tc is high, intrinsic electronic properties might render
applications rather difficult, particularly if extreme electronic anisotropy
prevents effective pinning of vortices and thus severely limits the critical
current density, a problem well known for cuprates. While many questions
concerning microscopic electronic properties of the iron pnictides have been
successfully addressed and estimates point to a very high upper critical field,
their application potential is less clarified. Thus we focus here on the
critical currents, their anisotropy and the onset of electrical dissipation in
high magnetic fields up to 65 T. Our detailed study of the transport properties
of optimally doped SmFeAs(O,F) single crystals reveals a promising combination
of high (>2 x 10^6 A/cm^2) and nearly isotropic critical current densities
along all crystal directions. This favorable intragrain current transport in
SmFeAs(O,F), which shows the highest Tc of 54 K at ambient pressure, is a
crucial requirement for possible applications. Essential in these experiments
are 4-probe measurements on Focused Ion Beam (FIB) cut single crystals with
sub-\mu\m^2 cross-section, with current along and perpendicular to the
crystallographic c-axis and very good signal-to-noise ratio (SNR) in pulsed
magnetic fields. The pinning forces have been characterized by scaling the
magnetically measured "peak effect"
Giant forced magnetostriction in Tb0.2Gd0.8 single crystal
The results of investigation of the Tb0.2Gd0.8 single crystal forced magnetostriction are presented. Temperature dependences of magnetostriction have been measured from 4 to 300°K in applied magnetic fields up to 14 T. The giant field induced magnetostriction ~ 1.5•10-3 was discovered in the room temperature region in magnetic fields up to 14 T
Giant forced magnetostriction in Tb
The results of investigation of the Tb0.2Gd0.8 single crystal forced magnetostriction are presented. Temperature dependences of magnetostriction have been measured from 4 to 300°K in applied magnetic fields up to 14 T. The giant field induced magnetostriction ~ 1.5•10-3 was discovered in the room temperature region in magnetic fields up to 14 T
Magnetoresistance of proton irradiated Si0.97Ge0.03 whiskers
Whiskers are a new material that is characterized by high structural perfection, chemical resistance and strength which reaches the theoretically possible limit for crystals of small transverse dimensions. The test whiskers were synthesized by the method of chemical transport reactions in a closed bromide system using gold as the initiator of growth. The crystals were irradiated by protons with an energy of 6 MeV and doses of 5×1013, 1015 and 1×1017 p+/cm2 at 40 °C in a U-120 cyclotron.
The effects of proton irradiation and high magnetic fields on the magnetoresistance of Si1-xGex (x = 0,03) whiskers in the 4.2–300 K temperature range has been studied. A slight decrease in the electrical resistance of the crystals in the 4.2–40 K temperature range during irradiation with small proton doses and a significant increase in their resistance in the entire investigated temperature range for a dose of 1×1017 p+/cm2 have been found. The ionization energy of the impurity atoms in different magnetic fields has been calculated. It has been revealed that the energy level of the impurity depends on the magnetic field but slightly which in turn indicates a independence of the concentration of holes on the magnetic field. It has been shown that a significant magnetoresistance at all studied temperatures was due to the magnetic field-caused decrease in the mobility of free carriers (holes). It has been found that the concentration of holes depends on magnetic field but a little. Conclusion has been made about a negligible expansion of the band gap in magnetic fields of up to 8 T