Memory effect in the high-temperature superconducting bulks

• Effects of temperature cycles on levitation force relaxation are investigated.
• Memory effect of the YBCO bulks is observed in experiments.
• With an increase of temperature, memory of the superconductor is gradually lost.

We present an experimental investigation of the relaxation of vertical force components in a high-temperature superconducting levitation system with different temperature cycle processes. For a selected ambient temperature (T1) of the system, the experimental results show that the relaxations of the levitation forces are strongly dependent on the initial temperature. When the sample was submitted to temperature jumps around T1, the sample temperature was regulated at T2, and there were two cases of the experiments, ΔT = T2 − T1 < 0 (negative temperature cycle) and ΔT > 0 (positive temperature cycle). It was found that in the case of negative temperature cycle, the superconducting samples have memory effect. And for the positive temperature cycle, with the experimental temperature increase, the memory effect of samples is gradually losing. Additionally, with the increase of temperature, the influences of the negative and positive temperature cycle on the levitation force relaxation are unsymmetrical. All the results are interpreted by using the characteristics of the free energy ‘ground’ plot of the Spin-glasses qualitatively.