(color online) The MFM images of the micron-size SM disk. (a) Schematic illustration of lithography-patterned arrays of soft Fe disks onto continuous Nd–Dy–Fe–Co–B hard-magnetic layer, and the well-coupled and decoupled structures are tuned by inserting a critical thickness of spacer layer. (b) Optical image of the disks array prepared by lithography technology. (c) and (d) The in-field MFM images of the well-coupled and decoupled disks, respectively. (e) and (f) Line profiles extracted from MFM images shown in panels (c) and (d), respectively.^[48]