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For toggle magnetic random access memory, the saturation field represents the exterior limit of the work region. Exterior magnetic fields higher than the saturation field lead to an irremediable loss of the stored information because the antiferromagnetic state of the synthetic antiferromagnetic (SAF) structure becomes a ferromagnetic state and data stored in the magnetic memory cell are altered. At the saturation point, the two ferromagnetic-layer magnetizations became parallel oriented, in a direction close to that of the applied field. In this paper, we present a method to find an analytical formula for the magnetic saturation field that depends on the angle between the applied magnetic field related to the easy anisotropy axis, on the amplitude of the antiferromagnetic coupling field between the ferromagnetic layers, on the geometrical characteristics of the SAF structure, and on the second term of the series expansion of the anisotropy energy of the system. This method allows us to obtain an analytical formula for saturation field that depends only on the controllable parameters of the SAF structure. This analytically obtained critical saturation curve perfectly matches with the critical saturation curve reported in previous papers.
Date of Publication: Dec. 2009