AC Hysteresis Loss, Lower Critical Field, and Critical Current Density at 77 K in Melt Processed YBa2Cu3O7−δ Wires and Rods

The AC hysteretic loss at 77 K in three samples of melt-processed YBa2Cu307-δ (YBCO) rods and wires has been measured over a wide range of applied field sweep amplitudes, Hm, using vibrating sample magnetometry. The results are discussed in two amplitude ranges, Hm H*, the latter being the penetration field. A magnetic method of ascribing an effective radius to cylinders of imperfect roundness is employed. From the heights of the hysteresis loops, the magnetic critical current density, Jc, is determined as a function of field strength. The per-cycle, per unit volume, hysteretic losses, Qh, are intercompared after having been normalized to a common reference sample radius, Rref. Loss differences that remain are ascribed primarily to differences in Jc. The hysteretic method is applied in determining lower critical field, Hc1. It was found that samples prepared using two variants of the melt-processing approach had Hc1s of 225 and 163 Oe. Two samples prepared independently by the same melt process had Hc1s of 163 and 162 Oe.