Critical state model and the magnetic behaviour of high T<inf>c</inf> superconductors

Intragrain critical current densities (Jc) are usually inferred from magnetization measurements using Bean's critical state model. Using this model results are presented for the case of Jc decaying exponentially with field and explanations are given for the observed changes in the shape of the magnetization hysteresis curve as (1) the sample temperature is changed; (2) the sample dimension is changed; (3) the maximum field to which the sample is cycled is varied; and (4) the field direction is changed for a single crystal sample. Some of the observed thermomagnetic history effects in the magnetization of the high temperature superconductors are also explained. Finally, d.c. and low-frequency a.c. magnetization data on various Rga2Cu3O7 superconductors are presented where features originating from intergranular and intragrain regions are identified and explained. © 1989.