High bias voltage effect on spin-dependent conductivity and low frequency noise in epitaxial Fe/MgO/Fe magnetic tunnel junctions

Low temperature (10K) high voltage bias dynamic conductivity (up to 2.7V) and shot noise (up to 1V) were studied in epitaxial Fe(100)/Fe-C/MgO(100)/Fe(100) magnetic tunnel junctions, as a function of the magnetic state. The MTJs show large TMR (185{\%} at 300K and 330{\%} at 4K). Multiple sign inversion of the magnetoresistance is observed for bias polarity when the electrons scan the electronic structure of the bottom Fe-C interface. The shot-noise shows a Poissonian character validating the high structural quality of the MgO barrier [1]. We have found that the normalized 1/f noise (Hooge factor) asymmetry between parallel and antiparallel states may strongly depend on the applied bias and its polarity. These MTJs exhibit record low Hooge factors being at least one order of magnitude smaller than previously reported [2]. ( [1] R. Guerrero, et al., Appl. Phys. Lett. \textbf{91}, 132504 (2007); [2] F.G. Aliev, et. al., accepted to Appl. Phys. Lett.).