Enhancement of switching stability of tunneling magnetoresistance systems with artificial ferrimagnets

In the study of spin dependent magnetic tunneling junctions, the switching stability of the magnetically hard layer is a crucial issue for long-term use in magnetic random access memory. After N switching cycles of the soft layer, the hard layer would be demagnetized due to the stray field from the domain wall created during switching of the soft layer. Therefore, reducing the stray field from the soft layer is the way to increase switching stability. In this study, we propose a structure which replaces the usual soft layer (typically permalloy, Fe, or Co) with an artificial ferrimagnet to reduce the stray field. The artificial ferrimagnet consists of a trilayer with an interlayer that antiferromagnetically couples two ferromagnetic layers of unequal thickness. The total stray field from the artificial ferrimagnet structure can be approximated as the sum of the stray fields from the two ferromagnetic layers. Since the sign of the stray field of the two layers is opposite, due to antiferromagnetic coupling, the total stray field is reduced due to cancellation. Since the magnitude of the stray field depends on the magnetic properties and the thickness of each layer and the distance from the magnetic layer, we can tailor the two magnetic layers of the artificial ferrimagnet structure to minimize the total stray field.