  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 $(47.2\pm 1.4)\%$ for the Hf-capped
sample was determined compared to the Ta one $(42.6\pm 0.7)\%$ 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.
