Anisotropic properties of spherical single crystals of La 1.8Sr 0.2CuO 4− δ

Abstract

Single crystals of La 1.8Sr 0.2CuO 4− δ grown by the traveling solvent floating zone method have been ground to spherical shape for studies of anisotropic superconducting properties by SQUID magnetometry. At low enough temperatures and fields, the spheres are perfectly shielding (susceptibility −1.5 [SI]) and thus magnetically isotropic. The field dependence of the critical temperature, the transition width and the field expulsion well below T c of the two crystals is detailed in this paper. The anisotropy of the first critical field when the applied field is parallel and perpendicular to the c-axis of the crystals amounts to about 3 and is within errorbars independent of temperature for both samples. Magnetization vs. field experiments along principal and intermediate field directions demonstrate the angular dependence of the hysteresis.