Magnetoresistance in doped magnetic tunnel junctions: Effect of spin scattering and impurity-assisted transport

The effects of spin-exchange scattering and impurity-assisted tunneling on the junction magnetoresistance (JMR) are investigated in magnetic tunnel junctions with artificially doped barriers. Spin scattering is observed when magnetic ions (Ni) are introduced, while for nonmagnetic dopants (Si), impurity-assisted tunneling occurs. The latter process is shown to be mainly elastic, and gives rise to an extra conductance that is unpolarized and reduces the overall JMR. In contrast, spin-exchange scattering is demonstrated to contribute inversely to the JMR, thereby decreasing it severely. The inelastic nature of spin scattering is reflected in a more pronounced temperature and voltage dependence of the JMR, as well as the junction resistance.