We have investigated the harmonic susceptibility chi-n = chi'n - i-chi"n (n = 1,2,3,...) of sintered YBa2Cu3O7 in the field of H(dc) + H(ac)sin-omega-t. chi'-1 and chi"-1 as functions of temperature depend on both H(ac) and H(dc). Both even and odd chi-n's were detected for nonzero H(dc), but only odd harmonics were observed for zero H(dc). At constant temperature, chi-n is an even function of H(dc) when n is odd while chi-n is an odd function of H(dc) when n is even. We compared experimental features with the prediction of the critical state model. For comparison, the static susceptibility chi-dc of YBa2Cu3O7 was examined as a function of temperature. The chi-dc(T) curve for the zero-field-cooled sample has a two-step structure like chi'-1. However, chi-dc(T) for the sample cooled in small fields is unusual; a negative peak occurs near T(c) and can be explained by flux depinning upon warming.
