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A self-consistent tight-binding method has been used to calculate the average magnetic moments of Ni N clusters between Nϭ5 and 16. The geometrical structures were taken from the results of moleculardynamics simulations with semiempirical potentials. The agreement with experiment ͑minima of at Nϭ6 and 13, and a maximum for Nϭ8) is good, and the variations of the average magnetic moment are explained as a consequence of geometrical effects: low coordinated atoms have large magnetic moments. Furthermore, the deviation of the interatomic distances from a smooth behavior also influences the magnetic moments. The contribution of the sp electrons to the magnetism is found to be relevant for Ni clusters with less than ten atoms. ͓S0163-1829͑97͒06219-X͔

We report an ab initio study of the interlayer exchange coupling in Fe/c-FeSi/Fe sandwiches and Fe/c-FeSi multilayers. We perform several structural studies, which show the stability of the CsCl arrangement seen experimentally for the spacer. We study the effect of pinholes, interface roughness, or structural misconfigurations of the spacer on the sign and magnitude of the exchange constant J. We have extended Bruno's theory to account for the effect of different effective masses on the exchange constant, leading to an excellent description of its asymptotic behavior, as compared with experiments. The results presented here allow us to identify Fe/c-FeSi sandwiches as an example of a new class of magnetic multilayer devices, where the spacer material is semimetallic.

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