Abstract
Experimental evidence of tremendous magnetic moment dynamical inversion, from metastable trapping state to the state with essentially the same moment oriented in the opposite direction, appearing during giant flux jump connected to thermomagnetic avalanche process in superconducting YBa2Cu3O7−δ single crystal, is presented. Magnetization inversion takes place in the system, without thermal contact between sample and sample holder, with a tremendous stored energy once the avalanche process is completed in quasi-adiabatic conditions. A model of magnetic moment inversion, caused by the jump between two metastable states of superconductor with the same energy storage, is presented and discussed in terms of the critical state with peculiar evolution of the critical-current spatial distribution. Importantly, knowledge of conditions of the appearance of such a phenomenon is crucial for applications of bulk superconductors as “permanent” magnets, for example, in superconducting levitation devices, etc.
Highlights
The magnitude of the critical current density, Jc, is a measure of the inhomogeneity of magnetic field distribution, caused by pinning of the magnetic flux in an external magnetic field H
The experimental evidence of magnetic moment inversion in superconducting YBa2Cu3O7−δ single c→ryst→al, without energy Etrn dissipation connected with the moment turning at zeroing magnetic field (Etrn ∼ M ⋅ H ), is presented in this
The observation presented here injects new dynamical feature of critical state of hard type-II superconductors: the jump transition from one branch of hysteresis loop in flux trapping regime to another one, i.e. jump from superconducting magnetic state characterized by magnetization value +M to that one characterized by −M or vice versa
Summary
A relatively large YBa2Cu3O7−δ single crystal of 2.67 × 2.69 × 2.55 mm[3] and 0.1184 g mass was utilized for magnetic studies. Such a fastening excludes the reversal of the sample in a magnetic field. Magnetolamination, explained in terms of the motion of twin boundaries, occurring under mechanical loading of the sample, was reported already in textured YBa2Cu3O7−δ superconductor[25] and was observed in the studied single crystal too (Fig. 1(b,c)). This phenomenon consists in mechanical lamination parallel to the ab-plane into thin platelets, due to pressure generated by strong magnetic field. A clear grid of parallel lines, which are the twinning surfaces that have come out of the bulk crystals, is visible
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