MAGNETIC-PROPERTIES OF THE TL2BA2CU1O6+DELTA 90K SUPERCONDUCTOR

We have measured magnetic properties of high quality Tl2Ba2Cu1O6+delta 90 K tetragonal superconducting and orthorhombic metallic non-superco nducting ceramics. The AC susceptibility shows distinct intra- and int ergrain transitions down to H=0.004 Oe rms. The field cooling measurem ent at 20 Oe shows a sharp transition at 90 K and 50% of full flux exc lusion at 5 K. At T>150 K, i.e. above the region where superconducting fluctuations contribute, the normal-state susceptibility is temperatu re independent and diamagnetic with a value of -5x10(-8) emu/g. The in tergrain critical current densities determined at B=1 T, using Bean's critical state model, are very low, 6x10(3) A/cm2 at 5 K and below 1 A /cm2 at 40 K.