We develop a fast numerical procedure for analysis of nonlinear and nonlocal electrodynamics of type-II superconducting films in transverse magnetic fields taking into account realistic boundary conditions. Using this procedure we explore stability of such films with respect to dendritic flux avalanches. The calculated flux patterns are very similar to experimental magneto-optical images of MgB2 and other superconductors, where the avalanche size and morphology change dramatically with temperature. We also find a threshold magnetic field, which agrees with both experiments and linear stability analysis. The simulations predict the temperature rise during an avalanche, where for a sub-microsecond time T ~ 1.5 Tc, and a precursor stage with large thermal fluctuations.
MgB2 tapes with high critical current have a significant technological potential, but can experience operational breakdown due to thermomagnetic instability. Using magneto-optical imaging the spatial structure of the thermomagnetic avalanches has been resolved, and the reproducibility and thresholds for their appearance have been determined. By combining magneto-optical imaging with magnetic moment measurements, it is found that avalanches appear in a range between 1.7 mT and 2.5 T. Avalanches appearing at low fields are small intrusions at the tape's edge and non-detectable in measurements of…
Thermomagnetic avalanches in superconducting films propagating extremely fast while forming unpredictable patterns, represent a serious threat for the performance of devices based on such materials. It is shown here that a normal-metal frame surrounding a selected region inside the film area can provide efficient protection from the avalanches during their propagation stage. Protective behavior is confirmed by magneto-optical imaging experiments on NbN films equipped with Cu and Al frames, and also by performing numerical simulations. Experimentally, it is found that while conventional flux cr…
First observation of flux avalanches in a-MoSi superconducting thin films
在Mo $_{84}$ Si $_{16}$非晶薄膜中观察到枝晶磁通雪崩的发生。这些事件被理解为具有热磁起源，并且涉及在有限的温度和磁场窗口内发生的磁通量突发的突然穿透。虽然直流磁力仪允许一个确定的阈值领域的热磁不稳定性的发生，磁光成像揭示了整个样品的磁通量的空间分布。进行适当的实验，典型的这一目标，雪崩被证实是这种材料的一个特性，排除了实验文物或功能相关的缺陷，在电影中的其他可接受的可能性。在本发明的观察之后，a-MoSi可以被包括在当以薄膜的形式时表现出通量雪崩的超导材料的图库中，当人们计划在应用中使用这些材料的膜时，必须仔细考虑这一特性。
We report on magneto-optical imaging, magnetization, Hall effect and magneto-resistance experiments in Nb/Al_2O_3/Co thin film heterostructures. The magnetic field is applied perpendicularly to the plane of the film and gives rise to abrupt flux penetration of dendritic form. A magnetization texture is imprinted in the Co layer in perfect coincidence with these ramifications. The spin domains that mimic the vortex dendrites are stable upon the field removal. Moreover, the imprinted spin structure remains visible up to room temperature. Complementary magnetization, Hall effect and magneto-resis…
Stability of the vortex matter -- magnetic flux lines penetrating into the material -- in type-II superconductor films is crucially important for their application. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger an electromagnetic breakdown. In this paper, we review recent theoretical and experimental results on development of the above mentioned thermomagnetic instability. Starting from linear stability analysis for the initial critical-state flux distribution we then discuss a numerical procedure al…
In this work, we provide a systematic study of the magnetic field penetration process and avalanche formation in niobium films of different thicknesses deposited on glass substrates. The research was carried out by means of direct visualization of the magnetic flux using magneto-optical imaging. The experimental data were compared with theoretical predictions for the development of thermomagnetic instabilities in the form of finger or dendritic flux avalanches in thin films. Analysis of the temperature and thickness dependence of threshold magnetic field at which superconductor first becomes u…
Active triggering and manipulation of ultrafast flux dynamics in superconductors are demonstrated in films of Nb. Controlled amounts of magnetic flux were injected from a point along the edge of a square sample, which at 2.5 K responds by nucleation of a thermomagnetic avalanche. Magneto-optical imaging was used to show that when such films are cooled in the presence of in-plane magnetic fields they become anisotropic, and the morphology of the avalanches change systematically, both with the direction and magnitude of the field. The images reveal that the avalanching dendrites consistently ben…
Onset of the transitional flux-avalanche regime in bulk NbTi controlled by the thermal boundary conductance
Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所）；O. Galkin Donetsk Institute for Physics and Engineering, National Academy of Sciences of Ukraine（乌克兰国家科学院奥·加尔金顿涅茨物理工程学院）
