High-Field Critical Current Properties of (Bi, Pb)2Sr2Ca2Cu3Oy Filaments

To understand the temperature, magnetic field, and angular dependence of the critical current density,
J
_c
(
T
,
B
,
θ
), of (Bi, Pb)
₂
Sr
₂
Ca
₂
Cu
₃
O
_y
(Bi2223) core composed of commercial Bi2223 tapes, we investigated
J
_c
(
T, B
,
θ
) of a bundle of Bi2223 filaments extracted from Ag-sheathed Bi2223 tapes under broad (
T
,
B
,
θ
) conditions. We found that flux pinning curves for
B
||
c
(
θ =
0°) exhibit a temperature-scaling relation at high
T
(50–77.3 K) but not at low
T
(30-40 K). We also found that
J
_c
(
θ
) exhibits a broad peak in the
B
||
ab
(
θ =
90°) direction and attributed it to the broadening of a sharp peak due to the intrinsic pin caused by a
c
-axis misalignment. We plotted
J
_c
(
T
,
B
,
θ
) as a function of the tape normal component of the magnetic field considering the
c
-axis misalignment, and it agrees well with the measured
J
_c
(
T
,
B
, 0°). This indicates that the intrinsic pinning is strong in Bi2223 and
J
_c
(
θ
) of Bi2223 is dominated by the flux pinning for the
B
||
c
component. Based on these findings, we succeeded in reproducing
J
_c
(
T
,
B
,
θ
) at 50-77.3 K by a model taking account of the
T
-scaling law,
c
-axis misalignment, and intrinsic pinning.