Large spin polarization in epitaxial and polycrystalline Ni films

The spin polarization (P) of tunneling electrons from epitaxial and polycrystalline Ni films was investigated using Meservey-Tedrow technique. The tunneling electrons from the Ni(111) surface were predominantly of majority spin, giving a P of +25%. This is the first observation of the P of tunneling electrons from Ni(111) in a planar tunnel junction. A large increase in P was observed for a polycrystalline Ni film (P = +46%) when the Ni surface/interface was cleaner. Our results point to the important role of localized minority d states near E_F in defining a higher majority P of the itinerant electrons seen in transport measurements, further showing the feasibility to tailor new materials with even larger P values.