Effects of defects on the switching properties of the nanostructured cells of a single layer and a synthetic ferrimagnet

The switching properties of nanostructured magnetic cells containing defects are investigated by using micromagnetic simulation. A particular emphasis is placed on the comparison of the results for the cells of a single magnetic layer (SL) and a synthetic ferrimagnet (SyF). A different switching behavior is observed in the relatively large cell sizes; the SL cells switch incoherently, but the SyF cells switch coherently, even though the thickness asymmetry of the SyF is quite large. The formation of vortices around the defects is mainly responsible for the incoherent switching in the SL cells, while the formation of a flux-closure structure is behind the reason for the coherent rotation in the SyF cells. At a small cell, suitable for high density magnetic random access memory (MRAM), however, the switching occurs coherently in both the SL and SyF cells. These results indicate that defects, which can be introduced to the cells during nanofabrication, do not significantly affect the switching properties and also the thermal stability of the high density MRAM cells.