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  • 11
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5711-5711 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There is experimental1 and theoretical2 evidence that the cubic Laves phase compound YCo2, paramagnetic at its equilibrium volume, will become ferromagnetic with only a slight increase in volume. This volume sensitivity of Co-containing Laves phase compounds must therefore be considered when addressing the problem of the origin of the Co magnetic moment in pseudobinaries RxY1−xCo2, where R is any rare earth element with a net spin moment. In this paper we augment the itinerant picture describing the effect of the rare earth spin on the Co magnetization3 by taking into account the changes in volume brought about by the substitution of the rare earth for yttrium. We obtained the coefficients of the Landau expansion of the free energy by fitting the expansion to the calculated energy versus moment curves of YCo2 for various volumes.2 (These energies were calculated in Ref. 2 using the fixed-spin-moment method, within the local-spin-density approximation). Thus, for example, the substitution of Gd forces the formation of Co moments not only because of the Gd spin, but because of the increase in latttice constant, whereas the rare earths heavier than Tb have smaller lattice constants and are less likely to induce a moment on the Co sublattice. Results are presented for the critical fields necessary for magnetic ordering and for the Co magnetic moment as a function of the rare earth substitution.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3359-3359 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the effects that an applied magnetic field has on the nature of the off-principal axis magnetic phases of rare-earth-transition metal pseudobinaries. The magnetic field is taken to be in the (01¯1) plane of these cubic materials but is otherwise arbitrary. Besides the expected second-order transition which takes place only when the field is in the [100] direction, there occurs a low-field first-order transition which separates two spin-canted phases. This transition is predicted for a range of concentration between the zero-field spin-canted/[111] boundary x0 and a somewhat larger concentration of [111]-easy rare earths x1. The field at the first-order transition is a monotonically increasing function of concentration within this range, starting at zero at x0 and reaching a critical field Hc of the order of D2/JMs at x1, where D is the fourth-order crystal-field strength and J is the exchange energy density. The point Hc, x1 is a critical end point in the H, x plane. The random fluctuations in sign of the crystalline field will most strongly effect the above results. Estimates of the effects of these fluctuations on the phase diagram will be made.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5987-5989 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: TbxDy1−x is probably the simplest example of a magnetic system with competing anisotropy. Tb and Dy are both low-temperature easy-plane ferromagnets with well-characterized anisotropy energies, such that Tb moments prefer the b axis in the hcp structure, while Dy moments prefer the a axis. It has been predicted, by a two-subnetwork approximation, that the low-temperature phase of the alloys with x between 0.86 and 0.76 exhibits a nonsymmetry direction of magnetization, a noncollinear spin structure, and 12th-order anisotropy. However, the two-subnetwork approximation is suspect when used to describe magnetic structure in alloys near phase boundaries, such as those between the ferromagnetic and the noncollinear phase. Using a probability distribution for site occupation, we have calculated the fluctuations of the spin orientation and the spin-spin correlation function as a function of composition in the noncollinear phase. The mean-square fluctuation in spin orientation is proportional to (xb−x)1/2, where xb is the critical concentration which separates the b axis ferromagnet from the noncollinear magnet. The average orientation also varies as (xb−x)1/2. Therefore, the simple two-subnetwork model is not valid near the phase boundaries. In fact, we find that the fluctuations from the average site occupation increase the range of stability of the noncollinear phase.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3649-3651 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two models of the magnetic structure of a ferromagnetic film deposited on a substrate are developed, with a view to explaining the reduced moment of Fe on GaAs. In the first, spin canting induced by antiferromagnetic exchange in the interface layer falls off rapidly in the interior of the ferromagnet, the characteristic distance being the size of the reconstructed magnetic unit cell in the interface. In the second, random anisotropy in the interface layer induces weakly pinned fluctuations of the magnetization which penetrate to a distance of order the domain wall width, approximately 100 A(ring).
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6983-6985 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic structure and hyperfine fields are calculated for antiferromagnetic YFe6Sn6 using the linear muffin-tin orbital method. The results show that Fe atoms have a strong ferromagnetic character with a full majority-spin band. The Fe moment is 2.2 μB while the Fermi contact term contributes a hyperfine field of 20 T at the natural lattice parameters. The hyperfine field is close to the experimental value of 22 T measured at low temperature. The calculation shows that the core s electrons contribute 24 T to the hyperfine field, but the 4s electron contributes 4 T in the opposite direction. Calculations using different unit cell volumes reveal that only the core electron contributions to the hyperfine field are proportional to the Fe magnetic moment with a conversion factor of 11.8 T/μB; the 4s contribution is not. The large local Fe moment and small hyperfine field are similar to those found in Fe2P and FeO. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Alimentary pharmacology & therapeutics 15 (2001), S. 0 
    ISSN: 1365-2036
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Iron supplementation may increase disease activity in ulcerative colitis, possibly through the production of reactive oxygen species from the Fenton reaction.〈section xml:id="abs1-2"〉〈title type="main"〉Aim:To assess the effects of two doses of oral iron on intestinal inflammation and oxidative stress in experimental colitis.〈section xml:id="abs1-3"〉〈title type="main"〉Methods:Colitis was induced in rats by giving 5% dextran sulphate sodium in drinking water for 7 days. First, using a 2 × 2 factorial design, rats with or without dextran sulphate sodium received the regular diet or a diet containing iron 3%/kg diet. Second, rats with dextran sulphate sodium-induced colitis were supplemented with iron 0.3%/kg diet and compared with rats on dextran sulphate sodium and regular diet. The body weight change, histological scores, colon length, rectal bleeding, plasma and colonic lipid peroxides, colonic glutathione peroxidase and plasma vitamin E and C were measured. Faecal analysis for haem and total, free and ethylenediaminetetra-acetic acid-chelatable iron was also performed.〈section xml:id="abs1-4"〉〈title type="main"〉Results:Iron 3% and iron 0.3% increased the activity of dextran sulphate sodium-induced colitis, as demonstrated by higher histological scores, heavier rectal bleeding and further shortening of the colon. This was associated with increased lipid peroxidation and decreased antioxidant vitamins. Faecal iron available to the Fenton reaction was increased in a dose-dependent manner.〈section xml:id="abs1-5"〉〈title type="main"〉Conclusions:Iron supplementation taken orally enhanced the activity of dextran sulphate sodium-induced colitis and is associated with an increase in oxidative stress.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Expert systems 5 (1988), S. 0 
    ISSN: 1468-0394
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Abstract: Knowledge acquisition has long been considered to be the major constraint in the development of expert systems. Conventional wisdom also maintains that the major problem encountered in knowledge acquisition is in identifying the varying structures and characteristics of domain knowledge and matching these to suitable acquisition techniques. With the aid of the first substantial systematic analysis of a sample of expert systems applications developed in the real world, the authors describe what is actually going on in terms of knowledge acquisition. In the light of the evidence, it is argued that a reappraisal of the conventional approach to knowledge acquisition is necessary.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Oxford, UK and Boston, USA : Blackwell Publishers Ltd
    Early medieval Europe 11 (2002), S. 0 
    ISSN: 1468-0254
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: History
    Notes: In the late eighth century, Charlemagne issued a new kind of land grant in Septimania and the Spanish March to refugees fleeing Muslim Spain. This grant, the aprisio, was made from fiscal land in deserted areas and included special rights and immunities. Previous scholars have interpreted the aprisio in economic and military terms as a mechanism to entice settlers to the region in order to make the land productive and to provide warriors to defend the Frankish frontier. This article suggests that political concerns also may have played an important role, arguing that the aprisio grant was an attempt by Carolingian kings to limit the power exercised by very powerful marcher counts.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Magnetism and Magnetic Materials 15-18 (1980), S. 593-594 
    ISSN: 0304-8853
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Magnetism and Magnetic Materials 54-57 (1986), S. 311-312 
    ISSN: 0304-8853
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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