Computer simulation of magnetization flop in magnetic tunnel junctions exchange-biased by synthetic antiferromagnets

Computer simulation in a single domain multilayer model is used to investig ate magnetization flop in magnetic tunnel junctions, exchange-biased by pin ned synthetic antiferromagnets with the multilayer structure NiFe/AlOx/Co/R u/Co/FeMn. The resistance to magnetization flop increases with decreasing c ell size due to increased shape anisotropy and hence increased coercivity o f the Co layers in the synthetic antiferromagnet. However, when the synthet ic antiferromagnet is not or weakly pinned, the magnetization directions of the two layers sandwiching AlOx, which mainly determine the magnetoresista nce, are aligned antiparallel due to a strong magnetostatic interaction, re sulting in an abnormal MR change from the high MR state to zero, irrespecti ve of the direction of the free layer switching. This emphasizes an importa nce of a strong pinning of the synthetic antiferromagnet at small cell dime nsions. The threshold field for magnetization flop is found to increase lin early with increasing antiferromagnetic exchange coupling between the two C o layers in the synthetic anti ferromagnet. The restoring force from magnet ization flop to the normal synthetic antiferromagnetic structure is roughly proportional to the resistance to magnetization flop. Irrespective of the magnetic parameters and cell sizes, the state of magnetization flop does no t exist near H-d = 0, indicating that magnetization flop is driven by the Z eeman energy. (C) 2001 Elsevier Science B.V. All rights reserved.