Impact of interfacial roughness on spin filter tunneling.

The impact of interface roughness on spin filter tunneling is considered at low biases as functions of temperature and barrier parameters. Roughness reduces the maximum achievable spin polarization, which results from tunneling ``hot spots'' (thin regions of the barrier) having intrinsically reduced spin filtering efficiency. Surveying a range of experimentally reasonable roughness and mean barrier thickness values allows us to conclude that roughness values greater than 10{\%} of the mean barrier thickness have an adverse impact on the spin polarization. Atomic-scale roughness may thus be critical for achieving 100{\%} spin polarization in spin filter tunnel junctions at low biases.