Field and temperature dependence of the anisotropy ratio in a high-$T_{\rm c}$ superconductor

P. Pugnat; G. Fillion; H. Noel; B. Barbara

doi:doi:10.1209/epl/i1996-00529-8

Field and temperature dependence of the anisotropy ratio in a high-Tc superconductor DOI: 10.1209/epl/i1996-00529-8

Europhys. Lett, 35 (1), pp. 49-54 (1996)

Field and temperature dependence of the anisotropy ratio in a high-Tc superconductor

P. Pugnat , G. Fillion , H. Noel and B. Barbara

Laboratoire de magnétisme Louis Néel, CNRS, B.P. 166, 38042 Grenoble Cedex 9, France
Laboratoire de chimie minérale B, Université de Rennes 1, CNRS, 35042 Rennes Cedex, France

(received 27 October 1995; accepted in final form 13 May 1996)

PACS. 74.50 - Proximity effects, weak links, tunneling phenomena, and Josephson effects.
PACS. 75.30Gw - Magnetic anisotropy.
PACS. 74.60Ec - Mixed state, critical fields, and surface sheath.

Abstract:

Using a double SQUID magnetometer, the angular dependence of the transverse (

) and longitudinal (

) components of the magnetization vector have been measured simultaneously on a

(

) and on a

(

) single crystal. The reversible and irreversible contributions of each component of the magnetization can be separated. The angular variations of the ratio of the reversible components

have been analysed with the 3D anisotropic Ginzburg-Landau theory. The derived anisotropy factor

is found to depend on the applied field. In

, this behaviour is attributed to field-induced reduction of the proximity effect of non-superconducting layers. In quasi-2D

, this interpretation is not relevant and our data show rather the lock-in transition of the vortex lines.