Magnetic anisotropy of high-Tc superconductors

The magnetic 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. The variations of ML and MT as a function of orientation, field, and temperature have been measured. In the regime where the simple three-dimensional anisotropic London theory is valid, it is shown that the measurement of MT/ML with an applied field in the range Hc1 H Hc2 yields the anisotropic mass ratio (m3/m1) directly. The possible breakdown of the simple theory is discussed.