C. A. Moyer

Particle capture by an assemblage of spheres in high‐gradient magnetic separation

We present a theory for the capture of magnetic particles by a bed of spheres in high‐gradient magnetic separation. The inviscid approximation to fluid flow is used in conjunction with an effective medium treatment to obtain the fluid velocity profile near a representative collector sphere in the assemblage. A similar idea is used to model the magnetic field, thus taking into account the effects of neighboring spheres. Results are reported for the capture of both paramagnetic and diamagnetic particulates by a filter operating either in the longitudinal or transverse design mode.

Crystallization, neutron irradiation, and annealing studies in glassy Ti50Be40Zr10

We have studied the crystallization and the effects of neutron irradiation and annealing on glassy Ti50Be40Zr10 (Metglas 2204) using resistivity measurements. The resistivity was measured from 2–1000 K for as-received Metglas 2204. Jumps in the resistivity were observed at the various stages during the crystallization process in agreement with previously reported results. Further, the negative temperature dependence of resistivity is affected by neutron irradiation and annealing. In both cases, interpretation of the results in terms of the Ziman theory of liquid metals indicates that the structure factor has sharpened. In the neutron irradiation case the structural relaxation is most likely the result of radiation enhanced diffusion due to the formation of vacancies.

A cluster model for localized moments in antiferromagnetic chromium

Recent studies of the magnetic susceptibility of chromium containing small amounts (<5%) of Fe impurity indicate that in the dilute limit the major contribution to the susceptibility comes from small clusters of Fe moments interacting among themselves via a strong ferromagnetic exchange coupling. We present a calculation of the susceptibility based upon a simplified model Hamiltonian which takes account of nearest neighbor exchange coupling of the local moments as well as their coupling to the spin density wave of the Cr host. In order to obtain reasonable quantitative agreement with experiment, the model requires a strong interaction between the moments and the spin density wave. We also find that moment pairs make the most substantial contribution to the overall susceptibility.

Coupling of localized spins in itinerant electron antiferromagnets

We obtain an effective spin Hamiltonian for a system of impurity spins embedded in an itinerant electron antiferromagnetic matrix. Each spin couples to the polarization field of the spin density wave via an s‐d exchange interaction with the conduction electrons. The impurity spins also interact among themselves via modulation of the existing spin polarization. The result is a generalized RKKY interaction whose long range oscillations reflect the Fermi wavenumber as well as the spin density wave periodicity.

Magnetic susceptibility and antiferromagnetism of dilute chromium‐osmium alloys

The magnetic susceptibility χ of Cr–Os alloys containing 0.3, 0.6, 1.1, and 2.0 at.% Os has been measured as a function of temperature T between 4.2 and 600 K. The χ vs T curves exhibit a well defined knee at the Neel temperature TN. TN increases with Os content, in agreement with earlier determinations from electrical resistivity data. at the Neel temperature TN. TN increases with Os content, in agreenment with earlier determinations from electrical resistivity data. The rise of TN is consistent with expectations based on the rigid band model for these alloys. The measured susceptibility in the antiferromagnetic regime below TN is compared with that calculated using the two‐band model for chromium. Variation in the size of the electron jack and hole octahedron upon alloying is taken into account within the rigid band approximation. The impurity and phonon‐scattering contributions to the susceptibility have been included. Agreement between theory and experiment is good over most of the temperature range, although discrepancies are apparent at low temperatures.