VECTOR MAGNETIZATION STUDIES OF ANISOTROPIC SUPERCONDUCTORS

The irreversible magnetic moment Delta m(ab) associated with fields applied parallel to the ab-plane of high-temperature superconductor (HTS) crystals provides a crucial measure of the inter-layer coupling. However, because these materials are so anisotropic, Delta m(ab) is small, and easily overwhelmed by the magnetization associated with in-plane screening currents. We show that even in the feast anisotropic HTS phase, YBa2Cu3O7, the field alignment with the ab-planes has to be within a fraction of a degree for Valid data on Delta m(ab) to be obtained. Furthermore, slight mis-positioning of the sample in the magnetometer sense coils can cause serious artefacts. The addition of a second signal channel to the magnetometer, in which the magnetic moment perpendicular to the applied field is also monitored, allows accurate alignment and enables reliable measurements of Delta m(ab) to be made.