Abstract
Magnetic tunnel junctions with two MgO barriers separated by a free CoFeB middle electrode have been investigated. As compared to single barrier junctions, the magnetoresistance increase due to annealing was smaller for these systems. The Néel coupling induced hysteresis shift of the middle electrode decreased, while coercivity and exchange bias field of the pinned ferromagnetic layers increased by increasing annealing temperature. For decreasing thickness of the middle electrode we observed that the contribution of the magnetoresistance of the upper barrier decreases probably due to the islandlike growth mode of CoFeB on MgO. Besides we found an increasing hysteresis shift of the middle electrode and additional dips in the major loops caused by magnetic interactions of the free middle electrode with the top pinned layer.
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