Transport critical-current density of superconducting films with hysteretic ferromagnetic dots

Abstract

Superconductor-ferromagnet hybrids present a rich and complex phenomenology. Particularly, a hysteretic behavior on the transport critical-current density, as a function of a uniform perpendicular applied field, has been experimentally found in superconducting films with some embedded ferromagnets. Here we analyze the interaction superconductor-ferromagnets by means of an iterative model based on the critical-state model with field-dependent internal critical-current density and compare the results with actual transport measurements. By using arguments of field compensation, we show how the change in the magnetization of the ferromagnetic inclusions is responsible for the observed hysteresis on the transport critical current.

Geometrically controlled ratchet effect with collective vortex motion

“…The asymmetry observed in the dissipation areas (figures 3(b) and (c)) is due to the asymmetry of the z-component of the field created by the SC. This self-field compensates for the applied field in the left part of the SC shifting the largest values of J c also to the left [19,20]. Although this model, being symmetric with respect to the direction of the current flow, does not account for the ratchet effect, it is consistent with the fact that the two regimes of dissipation appear.…”

“…Consider an infinitely long superconducting bar that contains several U-shaped notches (also infinitely long, simulating the blind-antidots). The calculation is based on assuming that the superconductor is in the critical state with a critical-current density depending on the local magnetic field through a Kim-type descending function [19,20]…”

Simultaneous magnetic and transport currents in thin film superconductors within the critical-state approximation

“…However, in some other geometries some previously induced magnetic currents can remain in the track and have some effect on the transport measurement. This is the proposed origin for the hysteretic transport measurements performed in tracks with holes [4].…”

Influences of Ferromagnetic Substrate on Microwave Surface Resistance of Type-II Superconductors

“…These studies were, later, expanded for different types of coating [14][15][16] and geometries [17,18]. Furthermore, vortex states and pinning properties for superconductor-ferromagnetic structures or ferromagnetic particles, dots, and pillars in superconductors have drawn tremendous interest [19][20][21][22][23].…”