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

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

doi:10.1209/epl/i1996-00529-8

All issues

Volume 35 / No 1 (July I 1996)

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

Abstract

Issue		Europhys. Lett. Volume 35, Number 1, July I 1996


Page(s)		49 - 54
Section		Condensed matter: electronic structure, electrical, magnetic and optical properties
DOI		https://doi.org/10.1209/epl/i1996-00529-8
Published online		01 September 2002

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

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

P. Pugnat¹, G. Fillion¹, H. Noel² and B. Barbara¹

¹ Laboratoire de magnétisme Louis Néel, CNRS, B.P. 166, 38042 Grenoble Cedex 9, France
² Laboratoire de chimie minérale B, Université de Rennes 1, CNRS, 35042 Rennes Cedex, France

Received: 27 October 1995
Accepted: 13 May 1996

Abstract

Using a double SQUID magnetometer, the angular dependence of the transverse (M_T) and longitudinal (M_L) components of the magnetization vector have been measured simultaneously on a ${\rm YBa}_2{\rm Cu}_3{\rm O}_{7-\delta}$ ( $T_{\rm c}\approx 91\;{\rm K}$ ) and on a $\rm La_{1.85}Sr_{0.15}CuO_4$ ( $T_{\rm c}\approx 35\; {\rm K}$ ) 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 $M_{\rm Trev}/M_{\rm Lrev}$ have been analysed with the 3D anisotropic Ginzburg-Landau theory. The derived anisotropy factor γ is found to depend on the applied field. In $\rm YBa_2Cu_3O_{7-\delta}$ , this behaviour is attributed to field-induced reduction of the proximity effect of non-superconducting layers. In quasi-2D $\rm La_{1.85}Sr_{0.15}CuO_4$ , this interpretation is not relevant and our data show rather the lock-in transition of the vortex lines.

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

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