Magnetic tunnel junctions with a magnetically soft Heusler-alloy electrode $({\mathrm{Co}}_2\mathrm{Mn}\mathrm{Si}∕\mathrm{Al}+\text{oxidation}+\mathit{\text{in}}\mathit{\text{situ}}\text{annealing}∕{\mathrm{Co}}_7{\mathrm{Fe}}_3∕{\mathrm{Mn}}_{83}{\mathrm{Ir}}_{17})$ and a maximal tunnel magnetoresistance effect of 86% at $10\mathrm{K}∕10\mathrm{mV}$ are investigated with respect to their structural and magnetic properties at the lower barrier interface by electron and x-ray absorption spectroscopy. A plasma-oxidation-induced $\mathrm{Mn}∕\mathrm{Si}$ segregation and oxide formation at the barrier interface is found, which results in a strongly increased area-resistance product of the junctions, because of an enlarged barrier thickness. For ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Si}$ thickness equal to $8\mathrm{nm}$ or larger, ferromagnetic order of Mn and Co spins at the interface is induced by annealing; simultaneously, atomic ordering at the interface is observed. The influence of the structural and magnetic interface properties on the temperature-dependent transport properties of the junctions is discussed.

• Received 18 March 2004

DOI:https://doi.org/10.1103/PhysRevB.70.024426