Superconducting fluctuation effect on epitaxially layered films of superconductor NbN and half-metallic Heusler alloy Co2MnSi

Superconducting properties were investigated in epitaxially layered films consisting of superconductor NbN and half-metallic Heusler alloy Co2MnSi (CMS). Temperature dependence of the electrical resistivity rho(T) was measured by applying perpendicular magnetic fields to the surface of NbN/CMS films. With the increase of the CMS thickness d(CMS), the upper critical field mu H-0(c2) decreased monotonically, but the superconducting transition temperature T-c had the minimum of 10.1 K at d(CMS) asymptotic to 5 nm. The T-c behavior was in qualitative agreement with the theory of the pi-coupling. The pair-breaking parameter delta determined by the superconducting fluctuation theory took the maximum at d(CMS) = 3 similar to 5 nm, which would be related to the minimum of T-c. The experimental results reveal that the superconductivity of the NbN layer in NbN/CMS films is affected by the interplay between the superconducting NbN layer and the half-metallic CMS layer.