ALBERT

Notes: As-deposited, magnetically soft nanocrystalline FeTaN films are successfully grown by dc-magnetron reactive sputtering. Growth conditions are instrumental in extending the solubility limit of Ta in the bcc FeTa alloy. Nitrogen incorporation in FeTa films is found to be much higher than in Fe films and can be explained in terms of thermochemistry using a large Ta-N interaction coefficient. The influence of different alloying elements is discussed theoretically, with regard to the metal-nitrogen affinity. A "typical columnar microstructure'' associated with the sputtering process is identified and its evolution versus the extent of nitrogenation is described in detail. Stress, magnetostriction, resistivity, and magnetic properties are respectively described as a function of both Ta and N contents of the films. The magnetic behavior of as-deposited nanocrystalline FeTaN is found to be very sensitive to both the dimension of the grains, their morphology and the nature of the grain boundary material which represents a non-negligible volume fraction in nanocrystalline films. It is proposed that the columnar structure plays the key role in promoting a large perpendicular anisotropy component (K⊥) and controls a "Stripe Domain''-like behavior observed at high N contents, which cannot be explained in terms of film stress in this material. The contribution of the magnetoelastic anisotropy is also described. In summary, by breaking the columnar structure, the incorporation of nitrogen first decreases K⊥ below the critical limit for formation of stripe domains. In these conditions, N acts as a "grain refiner'' and excellent soft magnetic behavior is reported and explained in terms of "vanishing magnetocrystalline anisotropy.'' The good thermal stability of such soft films is confirmed. By contrast, higher nitrogen incorporation increases K⊥ above the critical limit, leading to a stable stripe domain-like structure which does not allow for soft magnetic properties. This phenomenon has been found to be reversible at low temperature where a complete restoration of the soft magnetic behavior has been observed. This anomalous result is explained by the transformation of the grain boundary material into a "low Curie temperature phase'' for large N contents. © 1996 American Institute of Physics.

Notes: Domain structures in thin-film heads can be significantly influenced by magnetoelastic anisotropy. In this study we have undertaken systematic measurements of magnetostriction and stress in as-deposited and annealed states in FeN and FeTaN single-layer thin films with varying nitrogen contents. Magnetostriction was positive for FeN films, increased with increasing nitrogen content, and shifted toward negative values after annealing. Stress in as-deposited FeN films was tensile and decreased (became more compressive) with increasing nitrogen content. Annealing the FeN films resulted in significant stress relief. By contrast, magnetostriction was found to be negative for simple FeTa (zero nitrogen) and increased linearly with increasing nitrogen content to positive values. The magnetostriction in FeTaN did not change significantly after annealing at 200 and 250 °C. FeTaN film stresses were compressive in the as-deposited state and increased in magnitude (became more compressive) with increasing nitrogen content. After annealing these stresses were relieved slightly. Ta has been found to be very effective in enhancing the thermal stability of the FeN films. © 1996 American Institute of Physics.

Notes: In this study 2000 Å FeTaN thin films are annealed at 150 °C in both longitudinal and transverse magnetic fields. Both anneals result in a decrease in HK, which is shown to be a result of interstitial N, however, the transverse anneal results in a 90° rotation of HK and a 33% larger decrease in the magnitude of HK as compared to the longitudinal anneal. Subsequent transverse field anneals show that HK is completely reversible in relatively short times at any temperature above 75 °C. Our results are consistent with the diffusion of interstitial N being responsible for the rotatable behavior of HK in FeTaN. © 1999 American Institute of Physics.

Notes: This article presents a new method of investigating internal stress effects on thin film magnetic properties, in this case magnetically soft FeTaN sputtered films. The FeTaN films were deposited on a series of oxidized silicon (111) substrates prestressed to different degrees. During sputtering all the deposition conditions were kept exactly the same for all the samples. However, anisotropic stresses with different amplitudes are systematically introduced into the films when the prestressed wafers were released. In this way, FeTaN films with compressive stress varying from 80 to 608 MPa are produced. We found that the saturation magnetostriction (λs), anisotropy field (Hk), initial permeability (μi) as well as easy axis orientation of FeTaN thin films are strongly affected by the induced stress anisotropy. A stress ratio concept is proposed as a measure of the degree of the stress anisotropy. Models for easy-hard axis switching induced by stress for magnetic films with positive magnetostriction are discussed. © 1997 American Institute of Physics.

Notes: Exchange induced unidirectional anisotropy has been observed in a new bilayer system consisting of a ferromagnetic FeTaN or Ni80Fe20 film coupled to an antiferromagnetic Cr–Al alloy film. Estimates of the exchange coupling energy and magnetic anisotropy constant of the antiferromagnet are made and compared to other exchange coupled systems. © 1997 American Institute of Physics.

Notes: Abstract To determine the effects food ration and feeding regime on growth and reproduction of Strongylocentrotus droebachiensis (Müller), sea urchins in laboratory aquaria were fed kelp (Laminaria longicruris) supplied at either a high (H, ad libidum daily) or a low (L, ad libidum 1 d wk−1) ration in two successive 12-wk intervals during the reproductive period. After 24 wk, urchins fed the high ration continuously (HH) or for the last 12 wk only (LH) had a significantly greater mean gonad index [(gonad weight/total body weight) × 100] and body weight than urchins fed the low ration continuously (LL) or for the last 12 wk only (HL). Urchins in the HL treatment had a significantly greater gonad index than those in the LL treatment; there was no significant difference in gonad index between the LH and HH treatments. Females had a greater gonad index than males in the low ration (LL and HL) treatments at the end of the experiment; there was no significant difference between sexes in the high ration (LH, HH) treatments. Gametogenesis proceeded to maturation in all treatments and some individuals spawned at the end of the experiment. Females in the high ration (HH and LH) treatments had a greater proportion of nutritive phagocytes in their ovaries than females in the low ration treatments, but there was no effect of feeding treatment on oocyte or ovum size. Feeding treatment had no effect on the relative abundance of nutritive phagocytes in the testes, although the proportion of spermatocytes was higher (and that of spermatozoa lower) in the high ration than in the low ration treatments. Urchins in the high ration treatments had a lower mean jaw height index [(jaw height/test diameter) × 100] and greater mean test diameter than those in the low ration treatments at the end of the experiment, although these differences were not statistically significant. Feeding rate on kelp at the end of the experiment was significantly greater for urchins in the low ration than in the high ration treatments. Our experimental results show that even relatively low rations of kelp support somatic and gonadal growth in S. droebachiensis. Increasing the supply of kelp, particularly during the period of active gametogenesis, results in maximal rates of growth and reproduction. These results suggest that populations of S. droebachiensis in barrens may derive a substantial proportion of their nutrition from drift kelp, which may contribute to their persistence in these habitats. They also explain the large body size, high reproductive effort and fecundity of urchins grazing on kelp beds. These findings have important implications for understanding the dynamics of natural populations of S. droebachiensis and for development of effective aquacultural practices.

Notes: Abstract An analytical procedure for rapidly screening large numbers of oils for polychlorinated biphenyl (PCB) content has been developed and is now in routine use. Pontential levels of PCBs are inferred from chlorine concentrations as determined using the automated neutron activation analysis (NAA) facility at the Los Alamos National Laboratory Omega West Reactor. The technique is designed to screen up to 200 oil samples per eight hour working day, using a sample volume of approximately 1 milliliter. Because of the automated nature of the analysis, elements in addition to chlorine are determined, when present. These include fluorine, bromine, iodine and sulfur. U.S. National Bureau of Standards (NBS) and U. S. Environmental Protection Agency (EPA) Standard Reference Materials are routinely analyzed for quality assurance purposes. The results of our analyses of these materials for certified elements is discussed as well as results for other non-certified elements observed in the standard materials.

Notes: Abstract The fission fragment angular distributions from reactions of 140-MeV4He ions with238U,209Bi and197Au have been studied. From the anisotropies in the angular distributions, values forℊ eff, the effective moment of inertia at the fission saddle point, have been estimated and compared with results obtained at lower bombarding energies. The derivation ofℊ eff values has included corrections for the effects of incomplete fusion mechanisms on the orbital angular momentum distribution of the fissioning nuclei and for neutron evaporation prior to fission. The results are also compared with heavy-ion-induced fission data for systems of similar fissility. Also, examination of the forward-backward symmetry of the238U angular distribution substantiates other results which show that the fraction of fission reactions which follow complete fusion of the target and projectile is less than 0.5 for 140-MeV4He-ion bombardment of238U.