Magnetic Relaxation in a Y 0.5Lu0.5Ba2Cu3O y Superconductor at Various Magnetization Levels

The evolution of the rate of flux creep along the major hysteresis envelopes in a Y0.5Lu0.5Ba2Ca3Oy sample synthesized by a modified melt powder melt growth (MPMG) method at 25 K has been investigated. Magnetic relaxation rates depend strongly on the prior magnetic history. Calculations based on the critical state model can reproduce quite well the experimental data for magnetization when we have chosen the field exponent n = 0.3 in critical current density, Jc(Ha) = Jc0/(Ha−IM)n, where IM = Ha when 0 < H < Hc1 and (Formula presented.) when Ha ≥ Hc1. Using the field-cooled magnetization MFC data as well as the comparison of experimental and calculated M–H hysteresis loop, we estimated Hc1 = 500 Oe, p = 0, and the penetration field H∗ = 20 kOe. The apparent pinning energy was estimated as 62 meV for the remanent magnetization upon an excursion of 40 kOe.