Symmetry-state features in a global analysis of the temperature-dependent spin transport in Fe/MgO/Fe junctions
Résumé
The temperature dependence of the spin polarized tunnel conductance is investigated with Fe/MgO/Fe tunnel junctions with different structural properties and interfacial chemistry. A global quantitative model is proposed for analyzing the tunnel conductance in both parallel and antiparallel configuration. Three contributions to the temperature dependence can be distinguished. The first one is governed by the Bloch law for the temperature dependence of the magnetization of the electrodes. The second one is unpolarized and follows a power-law associated with a hopping mechanism. Although these two mechanisms are predominant in the decrease of tunnel magnetoresistance with temperature, a third contribution must be considered. This term results from a thermally activated decrease of the effective spin polarization, introduced by an Arrhenius law. It appears in either the parallel or antiparallel conductance, depending on the interface chemical doping, and could then be related to a symmetry dependent diffusion process. Finally, this global analysis appears universal, as it can well fit the temperature dependence of all samples.