Size and structural dependence of the magnetic properties of rhodium clusters

The size and structural dependence of the magnetic properties of (Formula presented) clusters (9⩽N⩽55) are studied by using a d-electron tight-binding Hamiltonian including Coulomb interactions in the unrestricted Hartree-Fock approximation. Three main different types of cluster geometries are considered (viz., fcc, bcc, and icosahedral). In each case the equilibrium bond length R is optimized by maximizing the cohesive energy (Formula presented)(N). The geometries yielding the largest (Formula presented)(N) alternate as a function of N. These structural changes, together with the variation of R, play a crucial role in the determination of the average magnetic moment μ-(Formula presented) of (Formula presented). The calculated size dependence of μ-(Formula presented) corresponding to the most stable geometries presents oscillations which are in good qualitative agreement with experiment. The magnetic properties of (Formula presented) clusters show a remarkable structural dependence which is characteristic of weak (unsaturated) itinerant ferromagnetism. The relation between the observed μ-(Formula presented) and the cluster geometry is analyzed. The role of nonuniform geometry relaxation, sp electrons, and sp-d hybridization effects are quantified for representative examples. Perspectives of extensions of this study are also discussed. © 1997 The American Physical Society.

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