Magnetic measurements on a rotated polycrystalline YBa2Cu3O7-δ (YBCO) disk at 4.2 K yield polar plots of the longitudinal-vs.-transverse components of the vortex flux density (B) relative to the fixed applied field (H) for various angles of rotation (θ) up to 360°. For the sample initially in a field-cooled (FC) state, detailed analyses of these plots reveal that B at any θ consists of a BR component, which rotates rigidly with the sample, plus a BF component, which stays at a constant frictional angle relative to H. At each H, BR and BF undergo large characteristic changes with θ until a rotational steady state is reached for θ above 180°. Strikingly, their numerical sum BR + BF is constant for θ up to ∼ 90°, then decreases linearly up to ∼ 180°, above which it remains constant at its reduced value. This reduction in BR + BF is attributed to an exiting of vortices from the sample, primarily those associated with the weakly pinned BF component. With increasing H, the relative vortex reduction rises to a broad maximum (of nearly 40%) and then slowly decreases, which reflects a competition between the intervortex repulsion and the confining forces produced by H. For the sample initially in a zero-field-cooled (ZFC) state, BR goes to zero while BF reaches the same steady-state value as in the corresponding FC case but without any vortex exiting from the sample.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering