Unusual Behavior of Antiferromagnetic Superconductors in Low Magnetic Fields

In this article, we examine the superconducting properties of low- and high-$T_c$ 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-$T_c$ superconductors can also be present in high-$T_c$ materials, however, they have not been observed for any non-substituted antiferromagnetic superconductors of the Y123 type. For the Gd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-\delta}$ compound, a peak in the temperature dependence of the ac susceptibility has been found for $x = 0.2$ 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 $x = 0.2$, 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. [2] D. Dhak, S. Hong, S. Das, P. Dhak, J. Nanomater. 2015, Article ID 723145, (2015). [3] A.J. Moulson, J.M. Herbert, Electroceramics: Materials, Properties, Applications, second ed., 2003, Wiley, Chichester, West Sussex. [4] K.F. Wang, J.M. Liu, Z.F. Ren, Adv. Phys. 58(4), 321-448 (2009). [5] J.A. Bartkowska, J. Dercz, J. Exp. Theor. Phys. 117(5), 875-878 (2013). [6] J. Kreiseli, M. Kenzelmann, Europhysics News 40, 17-20 (2009). [7] S.W. Cheong, M. Mostovoy, Nat. Mater. 6(1), 13-20 (2007). [8] N.A. Spaldin, M. Fiebig, Science 309, 391-392 (2005). [9] M. Fiebig, J. Phys. D: Appl. Phys. 38, R123 (2005). [10] D. Khomskii, Physics2, 20 (2009). [11] B. Wodecka-Dus, D. Czekaj, Arch. Metall. Mater. 56(4), 1127-1136 (2011). [12] H. Schmid, J. Phys.: Condens. Matter. 20, 434201 (2008).[13] G.A. Smolenskii, A.I. Agranovskaia, S.N. Popov, V.A. Isupov, Sov. Phys.-Tech. Phys. 3, 1981 (1958). [14] R. Sun, W. Tan, B. Fang, Phys. Status Solidi A 206(2), 326-331 (2009). [15] T.R. Shrout, A. Halliyal, Am. Ceram. Soc. Bull. 66, 704 (1987). [16] D. Bochenek, P. Kruk, R. Skulski, P. Wawrzała, J. Electroceram. 26, 8-13 (2011). [17] K. Wójcik, K. Zieleniec, M. Milata, Ferroelectrics 289, 107 (2003). [18] D. Bochenek, Z. Surowiak, Phys. Status Solidi A 206(12), 2857-2865 (2009). [19] X.S. Gao, X.Y. Chen, J. Yin, J. Wu, Z.G. Liu, M. Wang, J. Mater. Sci. 35(21), 5421-5425 (2000). [20] V. Bonny, M. Bonin, P. Sciau, K.J. Schenk, G. Chapuis, Solid State Commun. 102(5), 347-352 (1997). [21] O. Raymond, R. Font, J. Portelles, N. Suárez-Almodovar, J.M. Siqueiros, J. Appl. Phys. 99, 124101 (2006). [22] D. Bochenek, J. Dudek, Eur. Phys. J-Spec. Top. 154, 19-22 (2008). [23] D. Bochenek, Z. Surowiak, J. Krok-Kowalski, J. Poltierova-Vejpravova, J. Electroceram. 25, 122-129 (2010). [24] D. Bochenek, Eur. Phys. J-Spec. Top. 154, 15-18 (2008). [25] S. Matteppanavar, B. Angadi, S. Rayaprol, Physica B 448, 229-232 (2014)

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 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

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

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