MAGNETIC-PROPERTIES OF CUBO-OCTAHEDRAL ISING CLUSTERS

The magnetic properties of large Ising clusters with cubo-octahedral s tructures are studied. The Ising Hamiltonian is solved in the mean fie ld approximation and the magnetization and the Curie temperature are c alculated for clusters sizes up to 2057 atoms. It is found that the de pendence of T(c) with respect to the total number of atoms (N) follows a finite scaling behaviour delta = 1 - T(c)(N)/T(c)(infinity) = alpha N(-lambda). We find that lambda = 0.593 and alpha = 2.924, for the cas e in which the magnetic coupling constants between spins are independe nt of their location in the cluster. However, these quantities change considerably when the coupling constant between surface spins is assum ed to be different from the rest. These results clearly show the parti cular behaviour of finite aggregates. We present also the magnetizatio n profiles of the sites lying on the central plane of a cluster with 9 23 spins.