The differential conductance of NbN/GdN/TiN superconductor/ferromagnetic insulator/normal-metal junctions, with a thick NbN layer shows a large zero-field voltage offset interpreted as a spin-filtered Zeeman splitting of the NbN density of states by an effective exchange field $\left(H_0\right)$ from the GdN. The splitting increases linearly, with applied field $\left(H_{\mathrm{ext}}\right)$ enabling the relative sign of $H_0$ and $H_{\mathrm{ext}}$ to be determined. We show that the short NbN coherence length concentrates $H_0$ at the NbN/GdN interface and eliminates any averaging over the GdN domain structure leading to a large zero-field splitting.

• Received 9 April 2015
• Revised 28 October 2015

DOI:https://doi.org/10.1103/PhysRevB.92.180510