Properties of a large La 1.92Sr 0.08CuO 4+ δ single crystal grown by the travelling-solvent floating-zone method

Abstract

A centimeter size single crystal of La 2− x Sr x CuO 4+ δ (volume=1.32 cm 3) with x Sr=0.08 has been grown by the travelling-solvent floating-zone (TSFZ) method using a double ellipsoidal-type optical furnace as the heat source. The crystallised phase was checked solvent free by X-ray powder diffraction experiments, the crystal dimensions and quality being investigated by X-ray and neutron Laüe techniques. Several rocking curves of the Bragg peaks were performed by neutron diffraction giving a full width at half maximum (FWHM) of 0.200° for (006) reflection and clearly showing the presence of twin domains as expected for such an orthorhombic structure. The superconducting critical temperature of the as-grown crystal under 2 oxygen bar was determined by SQUID measurements with T c=18–20 K. Thermal treatments at different oxygen pressures were carried out showing no significant improvement of the transition sharpness and the T c value. Normal state susceptibility was also measured from 6 to 800 K for two different field orientations and can be interpreted as an antiferromagnetic insulating state behaviour. The resistivity measurements display an insulating behaviour perpendicular to the CuO 2 planes and a metallic behaviour in the planes, with a high anisotropy ratio R c / R b ∼350 at room temperature and a zero resistivity achieved at 27 K in both directions. The specific heat measurements have revealed no anomalies in the temperature range 15–300 K.