Temperature-dependent spin-transport and current-induced torques in superconductor/ferromagnet heterostructures*

Proximity effects at superconductor(SC)/ferromagnet(FM) interfaces provide novel functionality in the field of superconducting spintronics. We investigate the injection of quasiparticle spin currents in a NbN/Permalloy (Py) heterostructures with a Pt spin sink layer. To this end, we excite ferromagnetic resonance in the Py-layer via the microwave driving field of a coplanar waveguide (CPW). A phase sensitive detection of the microwave transmission signal is used to quantitatively extract the inductive coupling strength between sample and CPW as a function of temperature [1]. Below the superconducting transition temperature Tc, we observe a blocking effect of pure spin current transport in the NbN layer. Moreover, below Tc we find a large field-like current-induced torque. Our findings, reveal symmetry and strength of spin-to-charge current conversion in SC/FM heterostructures and provide guidance for future superconducting spintronics devices [2].

[1] A. Berger et al., Phys. Rev. B 97: 94407. (2018).
[2] M. Müller et al., arXiv:2007.15569.(2020).