Abstract
The AC hysteretic loss at 77K in three samples of melt-processed YBa2Cu3Ox (YBCO) has been measured using vibrating sample magnetometry. A magnetic method of determining the effective radius of imperfect cylinders is demonstrated. The hysteretic losses of various size samples are intercompared by normalizing the data to some arbitrarily chosen reference radius, Rref. Normalized loss then depends primarily on Jc. It is demonstrated that for field-sweep amplitudes, Hm, up to a few times Hc1 the Meissner surface current makes an important contribution to the total hysteretic loss, but that at higher fields, although still below the penetration value, H*, the loss can be closely approximated by the Hc1-ignoring Bean value, QhB, which follows the well-known law QhB∝Hm3. A hysteretic method of determining the lower critical field, valid for thick, high-Jc samples that defy the conventional M versus H approach, is described and demonstrated. Using this method, the 77-K Hc1s of YBCO prepared by two variants of the melt-processing method were found to be 225 and 163 Oe. The Hc1s of two samples prepared independently by the same melt process were found to be 163 and 162 Oe.
