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

Abstract

In this paper the origin of flux-jumps in Nb thin films is established during magnetization measurements using a vibrating sample magnetometer (VSM). Magnetization measurements of the flux avalanche activity show its strong dependence on frequency and amplitude of VSM vibration. In particular, under certain conditions the vibrations induce a transition from a stable superconducting critical state to an undercritical state, accompanied by the 20-fold drop in the magnetic moment. These features allow the elucidation of the origin of the flux-jumps. In contrast to the commonly assumed thermomagnetic instabilities to be responsible for the flux-jumps in Nb films, our results provide solid support for an alternative explanation being due to criticalitybuilt instability well represented by a sandpile. Considering properties of the flux-flow during a flux avalanche regime allows us to estimate nonuniformity of a magnetic field in a VSM sample space developed as a result of vibrations.

Fundamental dissipation due to bound fermions in the zero-temperature limit

“…In practice, the motion of the goalpost-shaped superconducting wire is hysteretic 27 due to the motion of flux lines or some other dissipation in the superconducting wire. Flux line motion, for example, would be driven by variation of the current used for moving the wire in the magnetic field, or by the effective change of direction of the external magnetic field when the legs of the wire are bent [42][43][44] .…”

Скачки Магнитного Потока При Намагничивании Пластины Сверхпроводящего Ниобия При Ориентации Магнитного Поля Нормально И Параллельно Поверхности

“…Измерения проводились с использованием вибрационного магнитометра VSM установки PPMS при скорости изменения магнитного поля от 10 до 130 Oe/s, в этом интервале влияния скорости развертки поля на зависимости M(H) не наблюдается. Для исключения возможного влияния повышенной частоты и амплитуды колебаний VSM на намагниченность сверхпроводника (эффект, наблюдавшийся для сверхпроводящих ниобиевых пленок в работе [18]) наши измерения проводились при малой частоте 7 Hz и малой амплитуде 1 mm. Для экспериментов использовалась однородно деформированная поликристаллическая ниобиевая фольга толщиной 100 µm, из которой были вырублены несколько образцов в виде дисков диаметром 3 mm.…”

Thermomagnetic instability and accompanied stress intensity factor jumps in type-II superconducting bulks under various magnetization processes

“…The nonlinear characteristic of the SC is described based on the Anderson-Kim flux-creep model, taking into account the dependences of critical current density on local temperature and magnetic field. It should be noted that the flux jump mechanism of bulk SCs can sometimes be explained by the self-organized criticality theory [38][39][40], in addition to the thermomagnetic instability theory. However, the flux jumps observed in BiSrCaCuO bulks during magnetization measurements exhibit a nature of thermomagnetic instability [9,10].…”