Evidence of anomalous vortex Hall effect in a ferromagnet/superconductor heterostructure

Abstract

The coexistence of superconductivity and ferromagnetism is a fascinating and complex phenomenon in condensed matter physics, as these two states are typically mutually exclusive due to their competing spin configurations. However, the interplay between these two orders has been a subject of intense research as it opens up possibilities for novel technological applications. Here, we report the coexistence of superconductivity and ferromagnetism in superconducting δ-TaN/ferromagnetic CoFeB heterostructures grown by facing-target sputtering. Superconducting states are comprehensively investigated, with evidence of correlation between superconducting and ferromagnetic order parameters. In particular, we observed an anomalous Hall signal without externally applied magnetic field in the mixed state near the superconducting critical temperature. The non-zero Hall resistance under varying temperatures and magnetic fields was systematically investigated. A possible mechanism associated with anomalous vortex Hall effect is proposed to explain the observed behavior, whereby superconducting vortices in the mixed state undergo transverse motions near the critical temperature. The concurrency of strong spin–orbit coupling, the superconductivity in the TaN layer, and the ferromagnetic ordering in the CoFeB layer offers new insights into vortex dynamics. Realizing this vortex dynamics spontaneously without an external magnetic field highlights the unique advantage of the TaN/CoFeB heterostructure, offering practical relevance for superconducting spintronic devices under zero external magnetic field.