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Results from recent calculations of the neutron-scattering cross section for energy transfer up to 1 eV have led to a new picture of spin waves in nickel, one in which spin waves exist out to the zone boundary. Our prediction of the dispersion curve and peak widths is in general agreement with data from subsequent neutron-scattering experiments. This provides additional evidence that the "average" spin-splitting energy for nickel is in the 300-to 400-meV range.

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An Fe/Au monatomic multilayer, consisting of alternating single Fe and Au layers, has been studied by means of the self-consistent full-potential linearized augmented plane wave method. We show by total energy minimization that this artificial thin film is in the tetragonal L1 0 ordered structure with the ratio of the interlayer spacing to the intralayer lattice constant at 0.865. In this configuration, the magnetic moment in each monolayer, the spin-polarized electronic density of states, and the corresponding band structure are calculated. The results are discussed in connection with recent experiments. ͓S0163-1829͑96͒04030-1͔

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Calculation of the magnetization, specific heat, and susceptibility of a Heisenberg ferromagnet with simple, face-centered, and body-centered cubic lattices have been made by terminating the first-order GreenVfunction equation in a manner similar to that suggested by Callen, who used a termination function a= (S Z )/2S 2 , based on certain physical criteria. We are led to the value a = (S*) 3 /2S 4 . For a= (S*)*/ 2S x+l there is no Curie point if x <1, and the magnetization M is double valued if 1

The coupled Green's-function equations for the Heisenberg ferromagnet are approximated by two coupled differential equations. The approximation agrees at low temperatures with Dyson's spin-wave theory. Computer solutions of spontaneous magnetization for spin \ and a face-centered cubic lattice represent a better fit to the magnetization of nickel than that afforded by an earlier first-order theory. Compared with the latter, the parameter 9 c = kT c /J for cubic lattices and for spin § is found to give closer agreement with values obtained from high-temperature series expansions. The renormalized exchange interaction, calculated for all temperatures below the Curie temperature, falls off with increasing temperature, and apparently represents a poorer fit to the experimental data than the results of the first-order theory.

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