Magnetic properties of Bi2Sr2CaCu2O8 single crystals with variable oxygen content

Abstract

The reversible magnetization of Bi2Sr2CaCu2O8 crystals was measured for the Hc direction. Crystals with different stoichiometry were obtained by quenching from different annealing temperatures between 450°C and 725°C, resulting in critical temperatures varying from 84 to 93 K. No large variations in the magnetization with Tc were found. The apparent increase of Tc with increasing magnetic field observed in previous work by other authors is not observed, leading to the conclusion that this effect may be caused by inhomogeneities in the oxygen content of the crystals. The magnetization of all specimens approximately followed a logarithmic decrease with increasing magnetic field for a given temperature, allowing the extraction of the magnetic penetration depth . The temperature dependence of does not follow the empirical [1-(T/Tc)m]-0.5, m=4 form, but requires values for m of slightly less than 2. The value for the zero-temperature penetration depth is 0.17 m, independent of specimen Tc. An attempt to fit the magnetization with a Ginzburg-Landau expression using a temperature dependence for Hc of the type Hc(T)/Hc(0)=1-(T/Tc)n with n=2 was not very successful, indicating that a more sophisticated analysis is needed. © 1992 The American Physical Society.