Frederick J. Milford

Quantum states of he atoms adsorbed on surfaces of rare gas solids

Wave functions and energies for band states of helium atoms in the two-dimensional periodic potential at the surface of a semiinfinite rare gas solid have been studied. In the case of Kr and Ar substrates, the atoms are highly localized and, correspondingly, the band widths are small. In a third case, namely that of an argon crystal highly compressed to simulate the adsorption site density of the close-packed face of argon, much larger band widths were found. If this is a reasonable simulation, then band effects may be observable.

Theoretical Solutions of Grain‐Boundary Diffusion Problem. Approximations and Interpretation of Experiments

Whipples exact solution to the idealized grain‐boundary diffusion problem has been evaluated numerically for ranges of parameters appropriate to existing and contemplated experiments. From these evaluations the concentration at the grain boundary, the integrated concentration at fixed depth of penetration, and the angle at which isoconcentration contours intersect the grain boundary are obtained, these results being presented in either tabular or graphical form. The ranges of validity of approximate solutions obtained by various authors are discussed on the basis of the numerical results, as is the use of the graphs and tables for the interpretation of experimental data.

The significance of many-body interactions in physical adsorption

The significance of many-body interactions in the physical adsorption of rare gas atoms on solid surfaces has been investigated. A simple model of the system was considered in which the atoms of the solid and the adsorbed atom were represented by interacting isotropic point dipoles. The fullN-body interaction energy between the adsorbed atom and the solid was calculated exactly to lowest order in the expansion parameter [αα0ηπ(ω0/ω)2]/4d3 (ω, α and ω0, α0 are the solid atoms and adsorbed atoms characteristic frequency and polarizability,d is the distance from the surface of the adsorbed atom, and η is the number of atoms per unit volume in the solid). The interaction was then evaluated for the adsorption of various rare gas atoms on rare gas solids. It was found that the fullN-body interaction deviated at most by only2 1/2% from the interaction obtained by considering only two-body interactions. In addition, it was found that a finite expansion in two-, three-, ... body expressions may lead to erroneous results for the interaction energy since extensive cancellations occur between successive terms of the series.

Renormalized Spin Waves in Ferrimagnets

The two‐time Greens function theories of Heisenberg ferromagnets have been generalized to treat ferrimagnets with arbitrary numbers of sublattices. The Tyablikov method of decoupling has been followed. A theorem due to Callen has been used to simplify the theory and to obtain a physical interpretation of the results. The renormalized sublattice magnetizations are expressed as the solutions to a coupled set of implicit equations. A second such set of equations determines a common Curie temperature for the sublattices of the ferrimagnet. Either set of equations can be solved numerically by iterative procedures which yield self‐consistent solutions. Renormalized spin‐wave frequencies are obtained which enter the theory in a manner which is consistent with the fact that the perfectly ordered spin state is not, in general, the ground state of a ferrimagnet. The sublattice magnetizations and Curie temperature have been calculated for magnetite and are compared with available experimental data.

The Impact of Physics on Technology and Industry

Physics has many facets. It is an assault on the frontiers of the known part of the physical universe aimed at increasing man’s knowledge of the universe in which he lives. Physics is also a beautiful intellectual exercise, the epitome of rationalism bringing together observation, experiment, deductive and inductive logic in a way seldom matched in other endeavors. It is also part of our cultural heritage which more people realize as more transparent ways of presenting physics are found. But it is also important to realize that physics and the other sciences have had great influence on material aspects of the way we live. This influence has been felt primarily through technology and industry and so it is worth examining the impact of physics on technology and industry.

SOME ASPECTS OF QUANTUM THEORY OF ADSORBED HELIUM FILMS

The main purposes of this paper are to provide background information for the theoretical papers that follow by Schick, Novaco and Woo and to review some recent developments in areas that these papers will not cover.

Magnetic Susceptibility of Mn++ IN CdS and Effects of Antiferromagnetic Exchange

This paper reports low-temperature measurements of the magnetic susceptibility of single crystals of CdS (in the hexagonal modification) with manganese impurity added. The data provide clear evidence for isotropic antiferromagnetic exchange interactions between next-nearest neighbor and in fact even more distant pairs of Mn++ ions. Antiferromagnetic effects in other dilute paramagnetic insulating crystals have been observed previously, as, for example, in susceptibility measurements on Cr+++ in A12O3 by Daunt et al.,1 on Mn++ in ZnS by Brumage et al.,2 in resonance measurements on platinum-diluted ammonium chloriridate by Griffiths and co-workers,3–5 on Mn++ in MgO by Coles, Orton and Owen,6 on Cr+++ in Al2O3 by Rimai et al.,7 and by Gill,8 and in optical observations on Cr+++ in A12O3 by Schawlow, Wood, and Clogston9, ‡ and on Mn++ in ZnS by McClure.11