  We report a two-step process for the fabrication of
superconductor-insulator-normal metal tunnel junctions using NbN as the
superconducting electrode and its surface oxide as the insulating tunnel
barrier, and investigate its efficacy in measuring spin-polarisation of
ferromagnets using the Meservey-Tedrow technique. We observe that for NbN film
thickness below 10 nm, under the application of parallel magnetic field, the
superconducting density of states show clear "Zeeman" splitting into spin-up
and spin-down sub-bands. Tunnelling measurements on devices where ferromagnetic
Co is used as the normal electrode shows that these devices can be used to
reliably measure spin polarisation of a ferromagnet at temperatures up to 1.6
K. The simplicity of our fabrication process, and the ability to perform
spin-polarisation measurements at 4He temperatures makes NbN a very attractive
candidate for spin polarisation measurements.
