Magnetization of submicron superconducting YBCO particles: isolated single vortices versus critical state model

• Published in: Physica. C, Superconductivity Superconductivity, 1996-11, Vol.272 (1), p.26-32
• Main Authors: Fleisher, V.G., Laiho, R., Lähderanta, E., Stepanov, Yu.P., Traito, K.B.
• Format: Article
• Language: English
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(96)00576-X

Strong suppression of the ratio of the thermoremanent ( M TR) and the field-cooled ( M FC) magnetizations M TR/ M FC, exceeding two orders of magnitude, when decreasing the size of superconducting YBCO particles from micron to submicron scale has been observed. A high saturation field ( H s > 8 kOe) of M TR ( H) in submicron particles excludes the applicability of critical state models for interpretation of the results. A model of trapping and relaxation of isolated single vortices in particles having size D ⪅ λ (λ is the magnetic field penetration depth) is introduced showing that interaction between a vortex and its mirror image results in a fast relaxation of M TR with size-dependent relaxation time τ ∝ D 2. The reduction of the remanence and its temperature and field dependencies in submicron particles are explained by the fast relaxation resulting in vortex-free particles and threshold fields of vortex trapping.