Simple calibration free method to measure ac magnetic moment and losses

Abstract

A calibration free method to measure components of a vector of ac magnetic moment in a transverse ac magnetic field have been developed. This method is oriented to study the features of the ac vector magnetization and losses in HTS tapes, wires and long slabs at low temperatures. The method is suitable for measurements in the case of a transport current carrying sample. The advantages of the method, besides its vector character, are an extremely compact ac field excitation coil and the pick-up coil positions outside with respect to the excitation one. Finite dimensions of the sample and pick-up coils are taken into account. To illustrate the potential of the method, the measurement of Bi2223/Ag tapes at 77 K were performed. The ac field amplitude 2–100 mT, the frequencies 20–230 Hz and various orientations of the transverse ac field to the sample plane were used. Besides, the dc magnetization and hysteresis losses of the samples were measured. The observed dependence of the ac magnetic moment on the angle between the ac field direction and the superconductor plane is consistent with the conception of the ‘Geometrical locking of the irreversible magnetic moment to the normal of a thin-plate superconductor’ (Zhukov A A et al. 1997 Phys. Rev. B 56 2809–19).