Shell Effect in Exchange Coupling of Transition Metal Dots and Their Arrays

On the basis of their electronic structure, we consider the magnetic properties of transition metal quantum dots and of arrays in which the dots are separated by nonmagnetic tunnel barriers. The oscillating size dependence of the magnetic moment of such strong ferromagnetic dots is well reproduced within a band structure-based shell model. If the dots are arranged in an array the analysis of the Nagaoka state of supermoments allows one to identify the conditions which lead to magnetic ordering. Our calculations compare favorably with recent experimental findings.