Electronic and structural characterization of LiF tunnel barriers in organic spin-valve structures

Abstract

The electronic, magnetic, and structural properties of Ni80Fe20 and Co electrodes at LiF and aluminum tris(8-hydroxyquinoline), or Alq3, interfaces were investigated with photoemission spectroscopy and polarized neutron reflectivity measurements. When LiF was deposited onto Ni80Fe20 films and Co was deposited onto thin LiF layers, the work function of both metals decreased. Polarized neutron reflectivity measurements were used to probe the buried interfaces of multilayers resembling a spin-valve structure. The results indicate that LiF is an effective barrier layer to block diffusion of Co into the Alq3 film. X-ray absorption spectra at the fluorine K edge indicate that no chemical reactions occur between Co and LiF. Despite these positive effects derived from the LiF tunnel barriers, there was no magnetoresistance in spin valves when the Alq3 layer was greater than 50 nm.