Vibration effect on magnetization and critical current density of superconductors

In this work the effect of vibrations on critical current density (J(c)) of superconductors has been studied. The vibrations are shown to affect J(c) of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of Jc as a function of magnetic field (B-a). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on J(c)(B-a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B-a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field (B-irr) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of B-irr for J(c) modeling is demonstrated.