Magnetotransport and microstructure of annealed magnetic tunnel junctions

We investigated the structural, the magnetic, the magnetotransport, and the tunneling properties of $\mathrm{CoFe}/{\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ junctions with an artificial ferrimagnet as a pinning layer for different Al thickness and oxidation time after isochronal annealing up to 500 °C. The main purpose of these experiments is to find relations between the structural changes upon annealing and the modifications of the physical magnetotransport and barrier properties, which could also be important for the further application of such tunneling elements in spinelectronics. The tunneling magnetoresistance (TMR) shows a strong increase up to 37% after annealing at 300 °C accompanied by an improvement of the dielectric stability and the voltage dependence of the TMR. At higher temperature, the TMR starts to decrease. The dielectric stability remains good up to annealing temperatures of 500 °C, indicating an excellent thermal stability of the ${\mathrm{Al}}_2{\mathrm{O}}_3$ barrier. All results can be related to thermally induced structural changes of the microstructure which have been determined by Auger depth profiling and complementary methods.