Vibrating-sample magnetization measurements were made of round Fe-clad monocore MgB2 wire fabricated by using a powder-in-Fe-tube technique. Magnetization, alternating-current loss, and transport measurements were reported. The M–H and loss measurements were made using a field sweep amplitude of 17kOe at 4 to 40K. In round monocore wire, the superconducting core was completely shielded against an external field of ±2kOe. At higher fields, a fixed ΔH was observed (partial shielding). It was found that the signal picked up by the vibrating sample magnetization was itself also partially shielded, i.e. reduced in magnitude during its return passage through the sheath, leading to a low field dip in the magnetization. FEM calculations of this latter effect were presented. The fact that the field which reached the inside of the conductor was less than the external field led to real loss suppression; even at moderate fields. The low field dip caused by a suppression of the signal emanating from the superconducting core led to an apparent loss suppression, i.e., the magnetically measured loss was less than the real (calorimetric) loss. The difference between real and apparent loss was estimated by FEM calculations, and the field sweep amplitude dependence of the 2 components was computed; neglecting the effects of partial flux penetration.

Real and Apparent Loss Suppression in MgB2 Superconducting Composites. M.D.Sumption, E.W.Collings, E.Lee, X.L.Wang, S.Soltanian, S.X.Dou, M.Tomsic: Physica C, 2002, 382[1], 98-103