In situ transport characterization of magnetic states in Nb/Co superconductor/ferromagnet heterostructures

Abstract

Employment of the non-trivial proximity effect in superconductor/ferromagnet (S/F) heterostructures for the creation of novel superconducting devices requires accurate control of magnetic states in complex thin-film multilayers. In this work, we study experimentally in-plane transport properties of microstructured Nb/Co multilayers. We apply various transport characterization techniques, including magnetoresistance, Hall effect, and the first-order-reversal-curves (FORC) analysis. We demonstrate how FORC can be used for detailed in situ characterization of magnetic states. It reveals that upon reduction of the external field, the magnetization in ferromagnetic layers first rotates in a coherent scissor-like manner, then switches abruptly into the antiparallel state and after that splits into the polydomain state, which gradually turns into the opposite parallel state. The polydomain state is manifested by a profound enhancement of resistance caused by a flux-flow phenomenon, triggered by domain stray fields. The scissor state represents the noncollinear magnetic state in which the unconventional odd-frequency spin-triplet order parameter should appear. The non-hysteretic nature of this state allows for reversible tuning of the magnetic orientation. Thus, we identify the range of parameters and the procedure for in situ control of devices based on S/F heterostructures.

Tuning superconductivity with spin–orbit coupling and proximity effects in ferromagnet/superconductor/ heavy metal heterostructures

“…T C , would be controlled by the SOC at the interface as the concentration of spin-triplet Cooper pairs is modified [33][34][35]. However, T C is also very sensitive to many factors, such as spin orbital torque generated by HM, the stray field of the F layer and the superconducting die layer in the F/S/HM system [36][37][38]. Therefore, it is a challenge to separate the contribution of SOC, and experimental confirmation is still lacking.…”