Magnetic properties of Co dot arrays grown on the N-modified Cu(001)c(2×2) surface

We present the magnetic properties of Co dot arrays grown on the Cu(001)c(2×2)-N substrate prepared by activated nitrogen bombardment. These Co dot arrays show ferromagnetic behavior above average Co thickness of 1.3 monolayer (ML), as evidenced by the existence of remanent magnetization which was measured by magneto-optical Kerr effect. It is also found that at Co coverages below 2 ML the magnitude of the remanent magnetization is always smaller than that of the saturated magnetization between 95 and 400 K. We discuss possible origins of the magnetic behavior, considered to be different from those of ultrathin films grown directly on the clean Cu(001) surface, in connection with the morphology of these dot arrays.