  We report on the strong influence of Carbon doping on 1/f noise in fully
epitaxial Fe/MgO(100)12ML/Fe magnetic tunnel junctions in comparison with
undoped junctions with a large density of barrier defects. Carbon influences
the relaxation of defects, the reconstruction of the interface and the symmetry
transformation of interface resonance states, which are suggested to contribute
to the strong reduction of the 1/f noise. Our study demonstrates that doping
with light elements could be a versatile tool to improve the electron transport
and noise in epitaxial magnetic tunnel junctions with large density of barrier
defects.
