Observation of dendritic flux instabilities in YNi2B2C thin films

Abstract

Magneto-optical imaging and magnetization measurements performed on thin films of the borocarbide superconductor YNi2B2C reveal the occurrence of magnetic flux instabilities upon reducing the applied magnetic field towards the remanent state. In contrast to other low-Tc materials such as Nb and MgB2, where similar instabilities occur in both increasing and decreasing magnetic fields, dendritic flux patterns are observed in YNi2B2C for decreasing fields only. Also in the magnetization measurements, a distinct asymmetry is evident between increasing and decreasing fields. The effect does not depend on the sweep rate of the field, but is strongly dependent on the maximum field applied before reduction. The observation of spontaneous flux instabilities in this additional family of low-temperature superconductors suggests that the responsible mechanism is universal to this class of materials.

Flux dendrites of opposite polarity in superconductingMgB2rings observed with magneto-optical imaging

“…Magnetisation measurements on MgB 2 thin films [95] soon revealed that flux jumps were ubiquitous below T ≈ 10 K: these jumps were later seen in MO experiments [96] displaying structures as the ones shown in figure 4.1. The phenomenon has later been observed in Nb 3 Sn, YNi 2 B 2 C, patterned Pb, and NbN, in all cases thin films [97,98,99,100]. Magnetisation measurements [101] on plain Pb films also hint strongly at dendritic avalanches below T = 3 K.…”

Visualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging

“…[9][10][11][18][19][20][21][22][23][24][25] Such behavior is intimately correlated to thermomagnetic instabilities experienced by the material when heat generated by a sudden displacement of vortices cannot be dissipated, creating thus an increase in the local temperature. This warmer region, in turn, has its pinning capability reduced, being thus likely to host even more vortex motion, reinforcing the process.…”

Ray optics behavior of flux avalanche propagation in superconducting films

“…These dramatic events occur due to a thermomagnetic instability [1][2][3][4] causing large amounts of flux to rush in from seemingly arbitrary positions along the edge. Magneto-optical imaging (MOI) of the flux penetration in films of many superconducting materials [5][6][7][8][9][10][11][12][13][14][15][16][17] has shown that it is a generic feature of these avalanches that they form nonrepetitive branching structures; see Ref. [18] for a review.…”