Magnetic interactions of supported magnetic clusters

It is demonstrated that the magnetic interactions can be drastically different for nano-sized systems compared to those of bulk or surfaces. Using a real-space formalism we have developed a method to calculate non-collinear magnetization structures and hence exchange interactions. Our results for magnetic clusters supported on a Cu(111) surface show that the magnetic ordering as a rule is non-collinear and can not always be described using a simple Heisenberg Hamiltonian. We suggest that ab initio calculations allowing for non-collinear coupling between atomic spins is the best tool for analyzing nano-sized magnets.