EVEN HARMONICS OF AC SUSCEPTIBILITY IN SOME SINTERED PELLETS OF HIGH-TEMPERATURE SUPERCONDUCTORS

The real (chi'n) and imaginary (chi''n) parts of even harmonic susceptibility (n less-than-or-equal-to 6) are measured as a function of external DC field (H(dc)) in the field increasing (Hup) and decreasing (Hdown) cycle. Hysteresis is observed between H(up) and H(down) cycles. In the H(down) cycle, at a field, H(comp) = 4.2G, both chi' and chi'' of all the even harmonics vanish indicating a true cancellation of fields in the intergrain region (H(eff) almost-equal-to 0) caused by the balance between H(dc) and the remanent magnetization of the grains. The position of the extrema and the zero of the various harmonics undergo a shift proportional to the remanent magnetization of the grains at that particular field.