Annealing effect on tunneling magnetoresistance in MgO-based magnetic tunnel junctions with FeMn exchange-bias layer

MgO-based magnetic tunnel junctions were fabricated, with a thin pinned CoFeB layer in the unbalanced synthetic antiferromagnet part of the stack FeMn/CoFe/Ru/CoFeB. Inverted and normal tunneling magneto resistance (TMR) values occur at low and high annealing temperatures (T(a)), respectively. The TMR ratio remains inverted up to T(a)=300 degrees C and it becomes normal around T(a)=350 degrees C. The exchange bias of FeMn disappears at high T(a). The sign reversal of the TMR ratio is mainly attributed to the disappearance of the exchange bias due to manganese diffusion during the annealing process. (C) 2009 Elsevier B.V. All rights reserved.