Recently, magnetic tunnel junctions with perpendicular magnetized electrodes combined with exchange bias films have attracted large interest. In this paper we examine the tunnel magnetoresistance of Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions in dependence on the capping layer, i.e., Hf or Ta. In these stacks perpendicular exchange bias fields of -500,Oe along with perpendicular magnetic anisotropy are combined. A tunnel magnetoresistance of $(47.2pm 1.4)%$ for the Hf-capped sample was determined compared to the Ta one $(42.6pm 0.7)%$ at room temperature. Interestingly, this observation is correlated to the higher boron absorption of Hf compared to Ta which prevents the suppression of $Delta_{textrm{1}}$ channel and leads to higher tunnel magnetoresistance values. Furthermore, the temperature dependent coercivities of the soft electrodes of both samples are mainly described by the Stoner-Wohlfarth model including thermal fluctuations. Slight deviations at low temperatures can be attributed to a torque on the soft electrode that is generated by the pinned magnetic layer system.
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