The magnetization anisotropies of Bi2Sr2CaCu2Oy and YBa2Cu3O7-x single crystals have been investigated by simultaneously measuring the longitudinal (ML) and transverse (MT) components of the equilibrium magnetization of crystals oriented at arbitrary angles with respect to the applied field direction using a superconducting susceptometer. In the regime where the simple threedimensional (3D) anisotropic London theory is valid, the measurement of MT/ML yields the anisotropic mass ratio (m3/m1) directly.
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1. INTRODUCTION Measurements of the upper critical field, Hc2, parallel and perpendicular to the basal plane of high-Tcsuperconductors indicate large anisotropy in the value of the Ginzburg-Landau (GL) coherence length in those directions.(l) Measurements of other properties also show anisotropy. The superconductivity of these materials has been speculated to be layer-like in the sense that it nucleates in the copper oxide planes which are in tum coupled by the Josephson effect,(2) Another possible source of anisotropy is unconventional pairing (3) which will not be considered here as it has not been demonstrated experimentally. There is also a possible crossover between the anisotropic 3D regime and the quasi-2D regime of weakly-coupled layers. In the latter regime, the system can exhibit 2D character, and is described by differential-difference equations, resulting in rather different behavior.(4) 2. THEORETICAL BACKGROUND The effective mass formulations of both the GL (5) and London (6) theories predict the existence of a transverse magnetization (perpendicular to B) in addition to the usual longitudinal magne-tization (along B) in the mixed state. Kogan has used the London theory to estimate the magni-tudes of both the longitudinal and transverse com-ponents of magnetization for a uniaxial supercon-ductor (ml = m2 :;:. m3).(7) Torque magnet-ometry studies of both YBa2Cu307-x and Bi2SQCaCU20y samples have been used to extract an anisotropic mass ratio. (8) The data is very clean but the fit depends not only on m3/ml, but also on other parameters which are not determined independently. However, simultaneous measurements of ML and MT provide a way to determine m3/ml directly without the use ofany additionalfitting parameters, as the ratio of transverse to longitudinal magnetization *Supported in part by the Air Force Office of Scientific Research under Grant AFOSR 87-0372 and by the Central Administration of the University of Minnesota. §Supported by the National Science Foundation Office of Science and Technology under contract STC-8809854. tSupported by the United States Department of Energy Office of Basic Energy Science / Materials Science under contract W-31-109-ENG-38.