Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

In antiferromagnetically coupled superlattices grown on (001) faces of cubic substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or Fe/Cr, the magnetic states evolve under competing influence of bilinear and biquadratic exchange interactions, surface-enhanced four-fold in-plane anisotropy, and specific finite-size effects. Using phenomenological (micromagnetic) theory, a comprehensive survey of the magnetic states and reorientation transitions has been carried out for multilayer systems with even number of ferromagnetic sub-layers and magnetizations in the plane. In two-layer systems (N=2) the phase diagrams in dependence on components of the applied field in the plane include ``swallow-tail'' type regions of (metastable) multistate co-existence and a number of continuous and discontinuous reorientation transitions induced by radial and transversal components of the applied field. In multilayers (N \ge 4) noncollinear states are spatially inhomogeneous with magnetization varying across the multilayer stack. For weak four-fold anisotropy the magnetic states under influence of an applied field evolve by a complex continuous reorientation into the saturated state. At higher anisotropy they transform into various inhomogeneous and asymmetric structures. The discontinuous transitions between the magnetic states in these two-layers and multilayers are characterized by broad ranges of multi-phase coexistence of the (metastable) states and give rise to specific transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio

Recent experimental results in sub- and near-barrier heavy ion fusion reactions

Recent advances obtained in the field of near and sub-barrier heavy-ion fusion reactions are reviewed. Emphasis is given to the results obtained in the last decade, and focus will be mainly on the experimental work performed concerning the influence of transfer channels on fusion cross sections and the hindrance phenomenon far below the barrier. Indeed, early data of sub-barrier fusion taught us that cross sections may strongly depend on the low-energy collective modes of the colliding nuclei, and, possibly, on couplings to transfer channels. The coupled-channels (CC) model has been quite successful in the interpretation of the experimental evidences. Fusion barrier distributions often yield the fingerprint of the relevant coupled channels. Recent results obtained by using radioactive beams are reported. At deep sub-barrier energies, the slope of the excitation function in a semi-logarithmic plot keeps increasing in many cases and standard CC calculations over-predict the cross sections. This was named a hindrance phenomenon, and its physical origin is still a matter of debate. Recent theoretical developments suggest that this effect, at least partially, may be a consequence of the Pauli exclusion principle. The hindrance may have far-reaching consequences in astrophysics where fusion of light systems determines stellar evolution during the carbon and oxygen burning stages, and yields important information for exotic reactions that take place in the inner crust of accreting neutron stars.Comment: 40 pages, 63 figures, review paper accepted for EPJ

Measurements of neutron emission induced by muons stopped in metal deuteride targets

An 80 MeV/c negative muon beam from the Alternating Gradient Synchrotron at Brookhaven National Laboratory was used to investigate the stopping of muons inside Pd, Ti and Y targets saturated with deuterium. Neutron emission from the targets was measured with an array of {sup 3}He detectors, and in some runs, the temperature of the target was monitored as a function of time, with and without a flux of muons on the target. The neutron rates were also measured for Pd cathodes in an active electrochemical cell similar in design to those used in so-called cold-fusion'' experiments, and the electrolyte solution was analyzed for excess tritium at rates consistent with these claimed in cold fusion'' experiments. Neutron production catalyzed fusion due to the presence of deuterium in palladium deuteride, PdD{sub 0.7}, exposed to muons was determined in palladium 0.0 {plus minus} 0.03 (stat.) {plus minus} 0.25 (syst.) neutrons per stored muon. 15 refs., 5 figs

INHALATION TOXICITY OF ZIRCONIUM COMPOUNDS. I. SHORT-TERM STUDIES

A total of 270 animals of 5 species was exposed by inhalation to compounds of zirconium for 6 hours per day, 5 days per week. One group of animals was exposed to ZrO{sub 2} at an atmospheric concentration of 75 mg. Zr/m{sup 3} for 30 days; another, to 11 mg. Zr/m{sup 3} for 60 days. A third group was exposed to a mist of ZrCl{sub 4} at a level of 6 mg. Zr/m{sup 3} for 60 days. Zirconium oxide produced no significant changes in mortality, growth rate, blood nonprotein nitrogen or fibrinogen, urinary protein, hematological values or histological structure. Zirconium tetrachloride at 6 mg. Zr/m{sup 3} gave questionable changes in blood hemoglobin concentration and red cell counts of dogs and a slight increase in mortality of rats and guinea pigs. Inhaled zirconium compounds deposited primarily in the lung and pulmonary lymph node, with a fraction of a per cent in the bone and considerably less in the soft tissues. (auth

Inhalation toxicity of zirconium compounds : I. Short term studies /

"Date Completed: 7/9/56; Date of Issue: 7/31/56."Account of work sponsored by a contract between the U.S. Atomic Energy Commission and the University of Rochester, and administered by the Department of Radiation Biology of the School of Medicine and Dentistry of the University."UR 460."Includes bibliographical references.Mode of access: Internet