Interplay of proximity effects in Nb/FePd heterostructures: domain-superconductivity, spin-triplet Cooper pair generation, and the impact on the ferromagnet

Proximity effects in superconductor/ferromagnet thin film heterostructures are highly topical issues due to their potential application in superconducting spin valves [1]. Physical properties can be controlled by an applied magnetic field and emerge for example as stray-field generated domain-superconductivity or spin-triplet correlations. Our goal is to investigate their interplay and tunability by an external magnetic field. We use a heterostructure system of Nb/FePd with varying strength of magnetic anisotropy and a lateral domain structure, grown by molecular beam epitaxy.

On the one hand, magnetoelectric transport measurements reveal a confined superconducting state due to the stray fields of FePd. On the other hand, direct proximity effects at the Nb/FePd interface with a non-collinear magnetization presumably lead to the generation of spin-triplet Cooper pairs with long penetration depth within the F-layer [3]. Grazing-Incidence Small-Angle Neutron Scattering (GISANS) probe exchange mechanisms on the microscopic scale and reveal a change in the ferromagnetic domain pattern by an onset of domain-superconductivity.

[1] J. Linder and J. W. A. Robinson, Nature Physics, vol. 11, pp. 307-315, Apr 2015.
[3] A. Stellhorn et al., New Journal of Physics, vol. 22, p. 093001, Sep 2020.