Anomalous vortex Hall effect in a superconductor/ferromagnetic heterostructure

Near the critical temperature (T_c) of superconductors, vortices in the mixing states will experience a transverse motion under external magnetic field and generate a Hall voltage, known as the vortex Hall effect (VHE). Over the last few decades, the VHE has been reported in both conventional superconductors and high-temperature cuprates. However, so far this effect has only been observed below or during the superconducting transition with the presence of the external magnetic field. Here, we report the spontaneous anomalous VHE without an external magnetic field in the mixing states both above and below T_c in the superconducting TaN/ferromagnetic CoFeB bilayer structures. Through the systematic characterization of the Hall resistance under different temperatures and magnetic fields, a sign reversal of the Hall voltage was discovered in the H-T phase diagram, indicating a change of vorticity above and below T_c. In addition, in the normal states, an anomalous Hall signal with a hysteresis loop is detected under in-plane magnetic field, suggesting the strong spin-orbit coupling in TaN may tilt the magnetic moment and generate an out-of-plane magnetic moment in the in-plane magnetic anisotropic CoFeB layer. The concurrency of strong spin-orbit coupling, superconductivity, and magnetism will provide insight into understanding the proximity-induced vortex dynamics and enable novel cryogenic spintronic device design.