Current density perpendicular to the tape plane: magnetic behaviour of silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Oxtapes for H // tape

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Abstract
We measured the magnetic properties of silver-sheathed Bi-2223 tapes with emphasis on the case where the magnetic field is parallel to the broad face of the tape (H // tape). All measurements were carried out at 77 K. Three regimes where found in which the mechanism determining the magnetic hysteresis is different. Regime 1 is defined by the irreversibility line for the case in which the magnetic field is parallel to the normal of the broad faces of the tape (H perpendicular to tape). For fields lower than this irreversibility field the magnetic hysteresis for H // tape is enlarged due to slight misalignments of the tape with respect to the magnetic field. No solution for the anisotropic critical state is found. In regime 2 just above this irreversibility line the current along the rolling direction (nominally the a, b direction) appears to be the limiting factor for the critical state. Resistively and inductively measured Jc are approximately equal. In regime 3 (still higher fields >or approximately=0.4 T) the critical state is determined by current transport along the thin direction of the tape, i.e. parallel to the average c axis of the grains. At around 0.4 T the effective current density perpendicular to the tape appears to reach several 100 A cm-2, quite a high value. The hysteresis (and thus this current) drops to zero between 0.8 and 1 T, depending on the tape measured. The implications for the current transport along the rolling direction of the tape are discussed.

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