Abstract
Vortex lattice melting for temperature near transition temperature T <sub>c</sub> was observed for 32 K superconductor (Bi <sub>1.6</sub> Pb <sub>0.4</sub> )(Sr <sub>1.5</sub> La <sub>0.5</sub> )CuO <sub>6+δ</sub> through the temperature dependence of magnetization in static applied field B <sub>a</sub> for both field-cooled (FC) and zero-field-cooled (ZFC) measurements. The irreversibility line (de-Almeida-Thouless line) H*(T) in the low field region (B <sub>a</sub> < 5 kG) was found to vary as (1-T/T <sub>c</sub> ) <sup>3/2</sup> . Low-field magnetic phase diagram shows very small lower critical field H <sub>c1</sub> (T) with H <sub>c1</sub> (0 K) = 26 G. The effects of grain geometry and magnetic relaxation are discussed.