We report studies on Andreev reflection measurements of ferromagnetic materials at junction interfaces using AlN/NbN junctions. We found that the junction resistance R can be controlled by varying the thickness and growth temperature of an AlN interlayer. The spin polarization of Co was determined to be PCo ≈ 0.44 from theoretical fitting of the conductance data for these junctions. The behavior of PCo and the dimensionless barrier parameter Z depending on the junction resistance R is discussed.
