Torque Study of Layered Superconducting OxideBi₂Sr₂CaCu₂O8+δSingle Crystal

Magnetic anisotropy of layered superconducting oxide Bi 2 Sr 2 CaCu 2 O 8+δ single crystal was investigated by torque measurements at 77 K. A hysteresis loop with a sharp cusp was found for the magnetic fields below about 6 kOe close to the ab -plane. It can be satisfactorily explained by assuming that the component of diamagnetic moment perpendicular to the ab -plane is induced by the applied external field. In fact, the field and angular dependence of the cusp is ruled well by the relation H cos θ= H c P , where H c P is the critical field perpendicular to the ab -plane at which the flux-pinning decreases abruptly with increasing field.