A novel approach towards manipulation of vortex matter in a superconductor with micromagnetic structures

Hard permanent magnetic materials offer a number of advantages over softer magnetic materials as sources of vortex pinning in a superconductor, like greater stability and larger magnetic field amplitudes. Permanent micromagnet structures prepared using thermomagnetic patterning (TMP) present an interesting and so far unexplored option for controlled artificial pinning.
We have investigated the vortex matter in superconductor/TMP micromagnet heterostructures (Nb-NdFeB) using quantitative Magneto-Optical Imaging (MOI). Comprehensive protocols have been developed for calibrating and converting Faraday rotation data acquired by MOI to magnetic field maps. These protocols reveal the comparatively weaker magnetic response of the superconductor from the background of larger fields associated with the magnetic layer in its vicinity. Further, TMP micromagnet structures have been imprinted in a Permalloy (Py) layer to obtain flexible magnetic landscapes for flux guidance in a Nb layer below it. Both smooth flux penetration and vortex avalanches in Nb are observed to be strongly influenced by the micromagnetic patterns. Our study offers new insights into the peculiarities of the vortex state in these superconductor-micromagnet heterostructures.