A new method for quantitative investigation of dissipative flux behaviour

In order to study the pinning force Fp of type II superconductors in a quantitative way, we first measured the internal friction (IF) during magnetization of Bi0.8Pb0.2SrCaCu2Oy superconductor and found that a characteristic IF peak occurs only if the sample is vibrating and the magnetic field is changing in time. The experimental results and theoretical deductions indicate that a non-linear force exists which is proportional to the product of the oscillating force on the magnetic flux (during IF measurement) and (Fd − Fp), where Fd is the driving force arising from the nonzero gradient of the flux density. Our analysis shows that if one can measure the absolute value of the d.c. magnetization against the external magnetic field, the pinning force for the sample can be determined quantitatively.