Magnetotransport properties and thermal stability of magnetic tunnel junctions with wave resonance plasma oxidized barrier

AlOx tunnel barriers prepared by oxidizing ultra-thin Al films of various thickness by means of a Rf wave resonance plasma beam source were investigated to understand the influence of the plasma oxidation conditions on the junction resistance Rj, the magnetoresistance ratio (MR) and the switching characteristics of exchange-biased magnetic tunnel junctions (MTJs) with NiMn pinning layer. The junction properties were characterized as a function of oxidation time, plasma power and distance between plasma source and sample. The MR of the as-deposited junction was about 15%. The highest exchange bias fields (17 mT) and pinned layer coercivities (23 mT) can be achieved with extended annealing at low temperatures T≅320∘C or with a rapid annealing at T≅400∘C, respectively. Short-time annealing (1 min) at intermediate temperatures (350 °C) and field cooling at 1 T leads to the highest MR effect of 35% at room temperature and 55% at 4.2 K.