Low writing field with large writing margin in toggle magnetic random access memories using synthetic antiferromagnet ferromagnetically coupled with soft magnetic layers

The authors propose free layer structures that can simultaneously reduce the writing field and enlarge the writing margin in toggle magnetic random access memories. In the free layers, two soft magnetic layers of NiFe and a synthetic antiferromagnet trilayer of NiFe∕Ru∕NiFe were ferromagnetically coupled through two ferromagnetic coupling layers (FCLs). The FCLs were composed of ultrathin Ta-based layers. As the coupling strength through the FCLs decreased, the spin-flop field (Hflop) decreased and the saturation field increased in these free layers, by which the Hflop could be freely decreased within the allowable range of its variation even for the 0.24-μm-wide bits.