A Comparative Study Between Electro and Magneto Excess Conductivities in FeTeSe Superconductors

We report here structural and fluctuation-induced excess conductivity in a FeTeSe superconductor by using the resistivity versus temperature measurements at different values of independent currents and applied fields (I = 1, 10, 50, and 100 mA, H = 0; H = 1, 3, 6, and 9 T, I = 10 mA). The prepared sample is investigated by using X-ray diffraction and standard four-probe technique using the resistivity option of PPMS-14 T. It was found that all peaks of the X-ray pattern are indexed as a tetragonal P4/nmm phase, and only a very small peak at about 2 ?? = 32.04^° is obtained. The lattice parameters are a = b = 3.802(5) Å and c = 6.070(2) Å, and the medium size of crystallites is about 32 nm. Regardless of magnetic field for simplicity and by using Aslamazov and Larkin expression, the logarithmic plots of Δσ and reduced temperature (ε), for both cases of different currents and fields, reveal three different conductivity exponents in the slope of each plot corresponding to two crossover temperatures. This is due to shifting of the order parameter dimensionality from short wave (SW) to two-dimensional/one-dimensional (2D/1D) and from 2D/1D to three-dimensional (3D), respectively. Furthermore, we estimated several physical parameters such as coherence lengths, Ginsburg number, anisotropy, G-L parameter, critical magnetic fields, and critical current density. Moreover, we follow Ullah and Dorsey field-dependent approximation for 3D and 2D analyses to obtain the fluctuation induced magneto-conductivity in the presence of magnetic field. Interestingly, the values of the slopes, deduced from logarithmic plots of 3D and 2D field dependence, are consistent with the values of SW conductivity exponents in the normal field region. In the mean field region, the values of the slopes for 3D are consistent with 2D conductivity exponents at H = 1, 3, and 6 T and with 1D at H = 9 T, while the values of the slopes for 2D are consistent with 3D conductivity exponents at H = 3, 6, and 9 T and with 1D at H = 1 T. As the field increases and keeping the temperature close to T _c, the 3D curves seem to be slightly open like a fan, while the 2D curves are collapse together.     

Superconductivity,Magnetism, and Magnetoresistancein RuSr<Subscript>2</Subscript>R<Subscript>1.4</Subscript>Ce<Subscript>0.6</Subscript>Cu<Subscript>2</Subscript>O<Subscript>10–δ</Subscript> (R = Eu,Sm)

Samples with nominal compositions RuSr₂R_1.4Ce_0.6Cu₂O_10–δ (R = Eu, Sm) were synthesized and their superconducting (SC) and magnetic properties were compared. A coexistence of AFM and FM ordering below the FM transition temperature was established in the two samples. It was shown that their SC properties are affected by a spontaneous vortex phase (SVP). The first critical fields of the two samples were calculate — H_cl≈ 70 Oe for R=Eu and 60 Oe for R=Sm. It was shown that the improved superconducting properties of the Sm-containing sample do not affect its FM behavior. A sizable magnetoresistance was observed in the two samples at T<T _c.     

Characterization of microstructural changes in an Al-6.8 wt.% Mg alloy by electrical resistivity measurements

Microstructural changes in an AlMg6.8 alloy after different thermo mechanical (TMT) and sensitization treatments were investigated by electrical resistivity measurements. The electrical resistivity was most affected by the content of Mg solute atoms in the α-Al matrix, due to β-phase precipitation, while contribution of the dislocation density to the resistivity of the AlMg6.8 alloy was less pronounced. The amount and distribution of the β-phase precipitated during sensitization were found to be strongly affected by the microstructure developed under the previously applied TMTs, i.e. by the dislocation density and the primary β-phase particles in the dual (α + β) phase structure. During sensitization of the specimens with a recovered/recrystallized dual (α + β) phase structure, precipitation of randomly distributed, globular β-phase particles occurred. Sensitization of cold deformed and recrystallized single α-Al structures induced β-phase precipitation in the form of a continuous layer along the shear bands/grain boundaries.     

Proximity Effect in Bulk LaBa2Cu3O7?y Samples with Ag Additions

Bulk LaBa ₂ Cu ₃ O _(7–y) samples with different Ag additions were investigated. It was shown that Ag does not enter the crystallographic structure of the superconductor and segregates on the grain boundary region. Current path in these samples occurs through the proximity-connected grains, and this was confirmed from the temperature dependence of the critical current density and mutual inductance. By using the theory developed for the thin-film structures, we conclude that growing of the Ag content increased the effective cross-section and the normal metal thickness. The effective cross-section prevails at low concentration, increasing the current. The normal metal thickness dominates at higher concentration, leading to saturation or even lowering of the critical current.     

Magnetic and Superconducting Properties of RuSr2Sm1.4Ce0.6Cu2O10−δ Samples

Samples with nominal composition RuSr₂Sm_1.4Ce_0.6Cu₂O_10−δ were synthesized at different conditions and their magnetic and superconducting properties were investigated. It was established that the magnetic order is of a long range type. It was shown that the increase of the oxygen content and the presence of larger microcrystals enhance the temperature of the onset of diamagnetism and the diamagnetic volume fraction of the samples, but do not significantly affect the temperatures of the intragrain superconducting and ferromagnetic transitions.     

Vortex Pinning Energies and H(T) Characteristic Lines in the MoSr2YCu2O8−δ Superconductor

We investigated the vortex pinning energies and H(T) characteristic lines of samples with nominal composition MoSr₂YCu₂O_8?δ . The vortex pinning energies were obtained using two approximations of the resistive transition. The characteristic lines H _c2(T) and H _irr(T) were obtained using resistivity, susceptibility and magnetization measurements. The values of H _c2(0) and different irreversibility field values are discussed.     

Effect of Sn-doping on the Superconducting Properties of HoBa2Cu3O y,Obtained by the MTG Method

Samples with nominal compositions HoBa₂Cu₃O _y and (Ho_0.97Sn_0.03)Ba₂Cu₃O _y are obtained by the melt-texture-growth (MTG) method and their superconducting properties are investigated. It is shown that the Sn-doping increases the irreversibility field and the upper critical field of the pristine compound. Both the undoped and Sn-doped samples undergo a vortex glass-vortex liquid transition. The observed phenomena are discussed.     

Power losses of Nb3Ge-clad tapes in superposed ac and dc magnetic fields

50 Hz power losses of Nb₃Ge-Cu substrate and Cu-coated tapes in parallel ac and dc fields of comparable magnitude have been studied. From the observed minimum in energy dissipation it is shown that the material exhibits a considerable surface barrier for initial flux entry into the superconductor.     

A new kinetic model for the common juniper essenstial oil extraction by microwave hydrodistillation

The main objective of the present study was to model the kinetics of essential oil extraction from swelled ground juniper berries by classic hydrodistillation (HD) and microwave-assisted hydrodistillation (MAHD). A new phenomenological kinetic model was developed on the basis of the juniper essential oil extraction mechanism that assumed three mass transfer processes occurring simultaneously: washing, unhindered diffusion and hindered diffusion. The new model was compared to the existing kinetic models. Among the tested models, the new model had the smallest mean relative percentage deviation and the highest corrected Akaike information criterion value. In addition, that, the new model was verified for HD and MAHD of essential oils from some other plant materials. On the basis of the above-mentioned facts, the new model can be recommended for modeling the kinetics of essential oil extraction by both HD and MAHD.