Topography of the Co grating and Ag/Co/Ag three-layer metal nanograting samples. (a) Schematic illustration of Ag/Co/Ag nanograting samples. Upper Ag layer of each sample is 5-nm thick, mid Co layer is 10-nm thick, and lower Ag layer is 35-nm thick. The total thickness of three layers of metal is fixed at 50 nm, which is the same as those of Co grating sample. (b)–(e) Atomic force microscopy image of the nanograting samples ((b) sample Co385, (c) sample ACA385, (d) sample Co325, and (e) sample ACA325, fabricated by interference lithography and DC magnetron sputtering. Cross-sectional profile of each sample is drawn along white reference line.