Arrays of magnetic nanodots on nitrogen-modified Cu(001) surfaces

A self-organized nanometre-scale pattern on a nitrogen-adsorbed Cu(001)-c(2x2) surface is used as a template for the fabrication of a magnetic nanodot array. By adjusting the coverage of nitrogen on this surface, 5 nm x 5 nm square patches of the c(2 x 2)-N surface can be arranged squarely and separated by 2 nm wide strips of clean Cu surface. Magnetic transition metals grow selectively on the clean Cu surface, and two-monolayers thick dots are dominantly formed at the intersections of the 2 nm wide Cu strips. Consequently, magnetic dots of a few nanometres in diameter are squarely organized with 7 nm intervals. Both the formation of the nitrogen-adsorbed nanopattern and the growth of the magnetic nanodots have been studied in detail by using scanning tunnelling microscopy and electron diffraction. Strain relief of the partly nitrogen-covered surface is the driving force producing the square arrangement of the nitrogen-adsorbed patches. The organization of the magnetic dots is ascribed both to selective nucleation of the magnetic metal dots on the clean Cu surface and to the large growth rate at the intersections. The magneto-optical Kerr effect is employed to examine the magnetic properties of the Co dot array. A long-range order among double-layer dots is established before their percolation occurs with increasing size. The origin of the novel magnetism is discussed. (author)