Field dependence of AC susceptibility and its anisotropy in a textured (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tape

Abstract

The AC susceptibility (ACS) of a well-textured (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tape was measured as a function of the externally applied DC magnetic field, temperature and the angle θ between the field and the tape plane. At a fixed temperature, both the real χ′ and imaginary χ″ parts of the ACS show a long-tail behaviour at low magnetic fields. As the field increases further, χ′ increases rapidly to a maximum value which is equal to the value above Tc while χ″ first raises and then passes a peak before going down to near zero. A χ″ peak of the ACS can be also obtained through changing the angle θ at a fixed field. These characteristics are demonstrated to be determined by the magnetoresistivity arising from the thermally activated flux flow (TAFF) rather than the shielding effect of the field-dependent critical current in the sample. The angular dependence of the ACS shows a scaling behaviour based on the three-dimensional (3D) anisotropic effective-mass model, contrary to the two-dimensional (2D) vortex pancake model. It is very interesting to note that this scaling can be obtained without any modification from the existing grain misorientations. The only result from the grain misorientations is the reduction of the experimentally derived anisotropic factor γ from the scaling law. From this nature we concluded that the 3D anisotropic scaling law can be applied for any preferred orientation system with γ parameter being a measure of the preferred orientation level in a sample.