Magnetic Relaxation in a Y0.5Lu0.5Ba2Cu3Oy Superconductor at Various Magnetization Levels

Abstract

The evolution of the rate of flux creep along the major hysteresis envelopes in a Y(0.5)Lu(0.5)Ba(2)Ca(3)Oy 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, J(c)(H-a) = J(c0)/(H-a - I-M)(n), where I-M = H-a when 0 < H < H-c1 and I-M = H-c1(p+1)/H-a(p) when H-a >= H-c1. Using the field-cooled magnetization M-FC data as well as the comparison of experimental and calculated M-H hysteresis loop, we estimated H-c1 = 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.