Current Flow and Flux Pinning Properties of YBCO Foam Struts

The current flow and the flux pinning properties on struts of superconducting YBa
₂
Cu
₃
O
_x
foams are analyzed in detail in the temperature range 60 K <; T <; T
_c
. For this purpose, magnetization loops were measured on foam struts taken from various positions of a 5 x 2 x 2 cm
³
large foam sample prepared at RWTH Aachen. From these data, the critical current densities, j
_c
, and the flux pinning forces, F
_p
= j
_c
x B, were calculated and pinning force scaling diagrams F
_p
/F
_p,max
versus h = H
_a
/H
_irr
were established. The scaling in the temperature range 60 K <; T <; 90 K was found to be well developed for all samples with peak positions, h
₀
, above 0.4, which is an indication of δT
_c
-pinning. The shape of the pinning functions is found to be completely different from all other high-T
_c
materials and varies only slightly with position. This specific dome shape cannot be described by an addition of several pinning functions, and the parameters p and q do not fit to the description of Dew-Hughes. Therefore, we employ Kramer plots to obtain more information on the flux pinning mechanism.