Vibration effect on magnetization and critical current density of superconductors

Abstract

. (2016). Vibration effect on magnetization and critical current density of superconductors. Superconductor Science and Technology, 29 075002-1-075002-12. Vibration effect on magnetization and critical current density of superconductors AbstractIn this work the effect of vibrations on critical current density ( Jc) of superconductors has been studied. The vibrations are shown to affect Jc 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 (Ba). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on Jc (Ba) 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 Ba 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 (Birr) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of Birr for Jc modeling is demonstrated. Abstract.In this work the effect of vibrations on critical current density (Jc) of superconductors has been studied. The vibrations are shown to affect Jc of all types of superconductors during their measurements, employing Vibrating Sample Magnetometer (VSM). Increasing vibration frequency (f ) and/or amplitude (A) lead to progressive reduction of Jc as a function of magnetic field (Ba). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on Jc(Ba) 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 Ba is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A is shown to have rather insignificant influence, while the vibrational vortex dynamics exhibits 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 Jc modeling is demonstrated.Vibration effect on magnetization and critical current density of superconductors 2

Interplay of Magnetization Dynamics with a Microwave Waveguide at Cryogenic Temperatures

“…Increasing magnetic field further beyond the field range in Fig. 5, the ZFC curve should coincide with the FC curve at the so-called irreversibility field [58][59][60] , where pinning of vortices becomes negligible. The FC curve in Fig.…”

“…For µ 0 H > 0.03 T the coupling remains by a factor of ∼ 2 higher than one for the ZFC curve. This difference is attributed to the fact that upon decreasing magnetic field, the Bean critical currents counter-act the Meissner currents, diamagnetic response of the superconducting film is reduced as compared to the ZFC measurement 60 , and the influence on YIG at the FMR decreases. Below 0.03 T, I drops rapidly, which can be explained by a gradual formation of a complex remanent critical state at H = 0 with highly nonuniformly distributed frozen magnetic flux.…”

Origin of magnetic flux-jumps in Nb films subject to mechanical vibrations and corresponding magnetic perturbations

“…More detailed discussions on the impact of the vibrations on the magnetization and critical current of the superconductors in the critical state can be found in Refs. [28,30,31]. In Fig.…”

“…2 and 3 in Ref. [28], or MgB 2 bulk [41]). The observation of flux avalanche activity at higher magnetic fields enables a more detailed investigation of corresponding dependencies on B a and/or measurement parameters.…”

“…Importantly, our measurements are carried out employing various frequencies and amplitudes of the VSM. In previous works [28,30,31], nontrivial effects of vibration on the field dependence of the critical current density [J c (B a )] have been established for various superconductors. The origin of the effect is due to movements of the samples in the slightly inhomogeneous field of the magnet or/and due to small sample displacements/tilt with respect to the magnet's axis.…”