Width-dependent upper threshold field for flux noise in MgB2 strips

Abstract

The authors measured magnetization hysteresis curves and used magneto-optical imaging to visualize the flux distributions in superconducting MgB2 films in order to study dendritic flux avalanches. The flux avalanches are found to disappear above some upper threshold field that is typically similar to 1 kOe, but strongly depends on the film width. If the film is made wider, this threshold field first increases and then tends to saturate. This behavior is quantitatively explained using a thermomagnetic model for the dendritic avalanches and taking into account the field dependence of J(c). The results demonstrate that patterning superconducting films into narrow strips substantially increases the range of magnetic fields for which they can be used for applications. (C) 2007 American Institute of Physics.