Growth and magnetism ofConanometer-scale dots squarely arranged on aCu(001)−c(2×2)Nsurface

We have studied the growth and magnetism of two-dimensionally coupled nanometer-scale Co dots which are squarely arranged on a $\mathrm{Cu}(001)\ensuremath{-}c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{N}$ surface. The morphology was analyzed by scanning tunneling microscopy, and the magnetization was studied using the magneto-optical Kerr effect. Well-ordered arrays of two monolayer (ML) thick Co dots interconnected by narrow 1 ML thick Co films can be grown by adjusting the deposited amount of Co. Here we used selective growth of Co at the clean Cu area of the surface, which consists of $5\ifmmode\times\else\texttimes\fi{}5 {\mathrm{nm}}^{2}$ N-adsorbed $c(2\ifmmode\times\else\texttimes\fi{}2)$ patches separated by clean Cu lines of a few nm in width. The observed ferromagnetism in these arrays is considered to be mediated by narrow monolayer thick Co films on clean Cu lines. When the average thickness of Co exceeds 1.5 ML, 2 ML thick Co dots are connected with each other, and 1 ML Co films grow on the $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{N}$ patches. For Co films with an average thickness between 1.8 ML and 2.1 ML, the magnetization is almost constant between 150 K and 370 K, and increases with decreasing temperature from 150 K. This result suggests that polarization is induced in the 1 ML Co film on $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{N}$ patches below 150 K.