P. Chowdhury

Superconducting properties of well-shaped MgB2 single crystals

We report measurements of the transport and the magnetic properties of high-quality, sub-millimeter-sized

Microstructure and pinning properties of hexagonal-disc shaped single crystalline MgB2

{mathrm{MgB}}_{2}

Peak anomaly and irreversible magnetization in Tl2Ba2CaCu2O8 single crystals

single crystals with clear hexagonal-plate shapes. The low-field magnetization and the magnetic hysteresis curves show the bulk pinning of these crystals to be very weak. The Debye temperature of

Field dependent creep characteristics in Tl2Ba2CuO6 single crystals

{ensuremath{Theta}}_{D}ensuremath{sim}1100 mathrm{K},

Transport and Magnetic Properties in MgB2 Single Crystals

obtained from the zero-field resistance curve, suggests that the normal-state transport properties are dominated by electron-phonon interactions. The resistivity ratio between 40 K and 300 K was about 5, and the upper critical field anisotropy ratio was

Dynamic vortex-phase diagram and noise property of MgB 2 single crystals near the peak-effect region

3.0ifmmodepmelsetextpmfi{}0.2

Equilibrium magnetization of Tl 2 Ba 2 CaCu 2 O 8 + δ single crystals

at temperatures around 32 K.

Effect of two bands on the scaling of critical current density in MgB 2 thin films

We synthesized hexagonal-disc-shaped MgB2 single crystals under high-pressure conditions and analyzed the microstructure and pinning properties. The lattice constants and the Laue pattern of the crystals from x-ray micro-diffraction showed the crystal symmetry of MgB2. A thorough crystallographic mapping within a single crystal showed that the edge and c axis of hexagonal-disc shape exactly matched the [10-10] and the [0001] directions of the MgB2 phase. Thus, these well-shaped single crystals may be the best candidates for studying the direction dependences of the physical properties. The magnetization curve and the magnetic hysteresis curve for these single crystals showed the existence of a wide reversible region and weak pinning properties, which supported our single crystals being very clean.

Peak effect and anomalous dynamic nature of a metastable state in Mg B 2 single crystals

Abstract Extensive measurements of the isothermal magnetization hysteresis with fields up to 5 T applied parallel to the c -axis have been carried out on Tl 2 Ba 2 CaCu 2 O 8 single crystals with T c ∼105 K. From these measurements, we determined the first penetration field ( H p ), the onset field of the second peak ( H on ), the second peak field ( H sp ), and the irreversible field ( H irr ). H p deviates from a linear to an exponential behavior at low temperatures, and H on decreases with decreasing temperature while H sp decreases with increasing temperature. H irr follows a power-law dependence down to temperatures of 45–50 K and then deviates to an exponential behavior at low temperatures. H p at low temperatures can be explained by using thermally activated pancake vortices on surface barriers. H on was well described by a theory based on a transition driven by disorder. At high temperatures, H irr may be compared with the melting line, as observed in BSCCO. At low temperatures, however, it is related to a surface barrier effect.

Magnetic relaxation inTl2Ba2CaCu2O8single crystals by SQUID magnetometer and micro-Hall sensor

The isothermal magnetization hysteresis loops were measured for Tl2Ba2CuO6 (Tl-2201) single crystals by using a SQUID magnetometer and a micro Hall sensor. In the temperature window from 15 to 30 K, the Hall sensor measurements for M(B) showed a second magnetization peak (SMP) at a peak field, Bsp, and an onset field, Bon. In this temperature region, the second peak appeared as a shoulder in the M(H) plots when measured by using SQUID. At a temperature of 20 K, time relaxation measurements for the time interval of 1–104 s were carried out at different fields by using a Hall sensor. From these relaxation data, for both flux exit and entry, the activation barrier, U0, and the creep exponent, μ, were separately calculated as a function of local field, Bz, by using the weak collective pinning theory. The variation of μ, and U0 as a function B indicates that below the onset of the second peak field, Bon, the creep mechanism is an elastic process, but above it, a gradual transition to plastic creep takes place. At higher fields, μ and U0 reduce sharply. This has been interpreted as a smooth transition to a 2D collective pinning state. These results are compared with that obtained in a double layer Tl compound, Tl2Ba2CaCu2O8 (Tl-2212),as well as other high-Tc materials.