Tunneling magnetoresistance of perpendicular CoFeB-based junctions with exchange bias

Abstract

Recently, magnetic tunnel junctions with perpendicular magnetized electrodes combined with exchange bias films have attracted great 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 dependent 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 ± 1.4)% for the Hf-capped sample was determined compared to the Ta one (42.6 ± 0.7)% at room temperature. Interestingly, this observation is correlated with the higher boron absorption of Hf compared to Ta, which prevents the suppression of the Δ1 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 which is generated by the pinned magnetic layer system.