Single domain observation for synthetic antiferromagnetically coupled bits with low aspect ratios

Arrays of the synthetic antiferromagnetic (SyAF) patterned bits were successfully fabricated with micron to submicron sizes. Magnetic domain structure was investigated using magnetic force microscopy (MFM) for the SyAF bits as well as monolayer bits. MFM image of ${\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}\text{(10\hspace{0.17em}}\mathrm{nm}\mathrm{)/}\mathrm{Ru}\text{(0.6\hspace{0.17em}}\mathrm{nm}\mathrm{)/}{\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}\text{(6\hspace{0.17em}}\mathrm{nm})$ SyAF bits demonstrates single domain structure for even a small aspect ratio of 1, while the 10 nm ${\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}$ monolayer bits showed multi-domain structure for the aspect ratios below 2. This result indicates the predominance of the SyAF for ultrahigh bit density magnetic random access memory devices, because the bits with aspect ratio of 1 possessing single domain structure can provide size-independent switching field.