Magnetic flux penetration into micron-sized superconductor/ferromagnet bilayers

Abstract

Flux penetration into small superconductor/ferromagnet elements is investigated by magneto-optical imaging and magnetic scanning transmission x-ray microscopy at low temperatures. It is found that penetration of magnetic flux into a thin bilayer of YBCO and Py strongly depends on the direction of a perpendicular magnetic field. The soft-magnetic layer acts as an amplifier for magnetic in-plane components that are generated by electric currents in the superconductor. These in-plane components point in opposite direction above the ferromagnet and below the superconductor. As a consequence a strong inclination of the local magnetic field occurs that significantly slows down or speeds up the flux penetration into such elements. From detailed magnetic scanning x-ray microscopy results it is found that the effect dramatically increases if the elements get smaller. In 20 × 20 μm2 superconducting squares we observe magnetic flux penetration that differs by more than a factor of four when reversing the external magnetic field.

Flux-pinning mediated superconducting diode effect in NbSe2/CrGeTe3 heterostructure

“…Asymmetric critical currents have also been observed in other works using conformally mapped nanoholes [13], size confinement in constrictions [2], and Josephson junctions [14,15]. It is plausible that asymmetric I-V characteristics can arise from extrinsic properties such as interface or edge roughness in lithographically defined constrictions [16] or other intrinsic mechanisms such as asymmetric vortex-flow energy barriers [1,17,18], magnetic flux penetration [19,20], flux pinning effects [21,22], vortex limited critical currents [23] and avalanches [24,25]. Hence, identifying the key driving mechanisms of the SDE and establishing their relations to other nonreciprocal transport effects is of paramount importance for future superconducting electronic as well as spintronic devices.…”

Phase-Field Simulation of Superconductor-Ferromagnet Bilayer-Based Cryogenic Strain Sensor

“…Recently, the effect of magnetic domain structures on the SC layer with emphasis on flux pinning has been reported using arrays of magnetic dots [6], magnetic templates [7], punch holes [8], magnetic nanorod array [9,10], magnetic stripes [11], domain width [12], and magnetic micro loops [13]. Such bilayer devices have also been proposed to be a candidate of memristor devices [14] and studied for superconductivity manipulation using FM domain structures with [15] and without [16,17] buffer layer.…”