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MAGNETIC MOMENTS INis that the individual atomic moments remain nearly constant throughout. Thus, the Fe moment remains within 10% of 2.8 ix B in both the Pd-Fe and Ni-Fe systems over a concentration range for which the average number of electrons per atom varies from 10-9. A similar property may be ascribed to the other atoms with characteristic moment values of 1.8 /*# per Co, 0.6 IIB per Ni and 0.4 JJLB per Pd. This atomic character of the moments in these face-centered cubic systems may well be explained by a partially localized-partially itinerant model. In this model the splitting of the d wave functions of t 2g and e g symmetry is accomplished not by a true crystal held effect, but rather by the overlap properties in this crystal structure of the two types of wave functions. The strongly overlapping t 2g functions are assumed to form a conventional band, and the fractional moments are attributed to exchange splitting in that band. The e g type functions do not *

We attempt to give a logically coherent definition of the term "sputtering threshold," and establish criteria which may determine an experimental threshold. The Silsbee chain mechanism and the experimentally observed preferred direction of emission from single crystals are used to establish a threshold theory. Two models are required, one generally applicable when the mass ratio is less than one, and another when it is greater than one. Single-crystal threshold laws are obtained, and polycrystalline laws follow for face-centered cubic crystals by averaging the single-crystal forms. An approximate technique for the evaluation of surface atomic binding energies is presented so that the thresholds can be compared with experimental results. In all cases the theoretical thresholds are less than or comparable to experimental "thresholds."

The sputtering yield S, in atoms/ion, has been measured for Cu and Ag single crystals bombarded at. normal incidence by 1-to lO-keV Ar+ ions. Yields of the three low-index planes (110), (100), and (111) for Cu and Ag crystals were measured as well as that of a Cu (311) plane. In addition a yield curve of a Cu (100) crystal bombarded in a [111J direction was measured. The yields were obtained by a weight loss method using ion beam techniques. The yields are strongly dependent on crystalline orientation showing a steep rise with energy, a maximum, which appears at an energy depending on the plane being bombarded, and a slow decrease with ion energy above the maximum. A simple theory is presented which accounts reasonably well for the energy dependence of the sputtering yield in terms of crystalline opacity and the momentum of the incident ion.