Mechanical Dissipation at Different Orientation of MagneticField in High-T_c Superconductor

The mechanical dissipation of (Bi_0.9Pb_0.1)₂ Sr₂ Ca₂Cu₃O_10+y and YBa₂Cu₃O_7-x ceramics were measured as a function of the angle θ between the orientation of the transverse magnetic field and the vibrating direction at fixed temperature and magnetic field with the vibrating reed technique. A relation between Q^-1 (or f) and The angle θ, i. e. Δ Q^-1 (or Δ f) ~ (H_a cosθ)^1.5 was found and this indicated that only the magnetic field component parallel to the vibrating direction H_a cosθ gives rise to the enhancement of internal friction and resonant frequency in ceramic sample. The anisotropic deformation of flux-line-lattice is used to explain the observed results.