MAGNETIC-PROPERTIES OF A TL0.5PB0.5SR2CACU2O7 SINGLE-CRYSTAL

High-quality millimeter size single crystals of Tl0.5Pb0.5Sr2CaCu2O7 with T(c) = 82 K have been synthesized for the first time. The regularity of their structure has been checked by using X-ray diffraction techniques and electron microscopy. Magnetic measurements have been performed in the geometry B parallel-to c. Fitting the reversible magnetization versus B with the London model yields the temperature dependences of both lambda(ab) and H(c2). From these results the following superconducting parameters have been obtained: (-dB(c2)/dT)Tc = 1.71 T/K, xi(ab)(0) = 1.92 nm and lambda(ab)(0) = 173.9 nm. Furthermore, Tl0.5Pb0.5Sr2CaCu2O7 single crystals exhibit the highest irreversibility line B*(T/T(c)) among all the single crystals of thallium cuprates. Moreover a scaling of the hysteresis loops M(B) can be performed in a wide range of temperature. All these data are discussed in connection with the structural parameters of Tl0.5Pb0.5Sr2CaCu2O7.