Anisotropic properties of spherical single crystals of La_1.8Sr_0.2CuO_4-\delta

TL;DR

This study investigates the anisotropic superconducting properties of spherical La_1.8Sr_0.2CuO_4-elta crystals, revealing isotropic behavior at low temperatures and fields, with notable differences in magnetic hysteresis and critical current densities along different crystallographic directions.

Contribution

The paper presents a novel spherical crystal shape for La_1.8Sr_0.2CuO_4-elta, enabling detailed anisotropic magnetic property measurements and revealing new insights into critical current behavior.

Findings

Spheres are perfectly shielding and magnetically isotropic at low temperatures and fields.

Field dependence of T_c and transition width is similar in different directions.

Large hysteresis difference and enhanced critical current density along CuO_2-planes.

Abstract

Single crystals of La_1.8Sr_0.2CuO_4-\delta grown by the travelling solvent floating zone method have been ground to spherical shape for studies of anisotropic supercondcucting properties by SQUID magnetometry. Here we report on magnetization measurements parallel and perpendicular to the c-axis on two of these crystals. 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 is qualitatively similar in both samples and is detailed in the paper. The anisotropy of the first critical field also shows similar behavior for the two crystals. Magnetization vs field experiments reveal a large difference in the hysteresis behavior along the two directions and an enhancement of the critical current density through the CuO_2-planes compared to the in-plane current density at higher fields.