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  • 1
    Electronic Resource
    Electronic Resource
    Surface roughness and long-range order of a semi-infinite ferromagnet : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5981-5983 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider the effect of random surface roughness on a semi-infinite ferromagnetic film. We calculate the magnetization as a function of distance from the surface and the spin-spin correlation as a function of lateral separation. We show that, even in the absence of crystalline anisotropy or an external field, the surface of the ferromagnet is stable against random torques created by the roughness. Near the surface, the magnetization reduction is inversely proportional to the square of a "healing'' length λ0≡(D/2πM0)1/2, where D is an exchange stiffness and M0 is the saturation magnetization. The correlations in fluctuations of the magnetization orientation decay exponentially with distance parallel to the surface, λ0 being in the exponent. In contrast, fluctuations decrease only as the reciprocal of the square of the distance perpendicular to the surface. Results are discussed and compared with other calculations of the effects of random surface perturbations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353490
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  • 2
    Electronic Resource
    Electronic Resource
    A phenomenological theory for the temperature dependence of the antiferromagnetic coupling in thin-film sandwiches and multilayers (abstract) : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5879-5879 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent magnetoresistance experiments1,2 on Fe/Cr/Fe sandwiches and superlattices show that the critical magnetic field for saturation varies linearly with temperature from liquid helium to room temperature. The drop in critical field is as large as 30%, even though the reduction in Fe magnetization is negligible over this temperature range. In order to gain some insight into the physical origin of this softening of the critical field, which is a measure of the antiferromagnetic interlayer coupling, we have studied a phenomenological model of an Fe/Cr/Fe sandwich structure which consists of two Fe films coupled at their interface by an antiferromagnetic exchange at zero temperature. The Fe films themselves are ferromagnetic and subjected to an external field and uniaxial in-plane anisotropy. The Fe spins are confined to the film plane. The temperature dependence of the critical field, i.e., the field below which the spins in the two films deviate from the direction of the field, arises from fluctuations in these spin deviations, which are present for any temperature greater than zero. Using an approximation in which these fluctuations are treated classically, the critical field decreased linearly with temperature, with a coefficient that increases logarithmically with the transverse dimension of the films. Interpreting this length to be of the order of the grain size in polycrystalline films or a coverage terrace width in epitaxially grown material, we can directly relate the temperature variation of the antiferromagnetic interaction to film quality. The larger this dimension, the greater the decrease of the coupling with temperature; hence, "better'' films are expected to show weaker (or zero) coupling at room temperature. Conversely, the magnetization of the Fe films is not critically dependent on this dimension. Extension of the model to include spin-wave effects will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350117
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of volume on magnetization in RxY1−xCo2 pseudobinaries (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5711-5711 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.348939
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  • 4
    Electronic Resource
    Electronic Resource
    Amorphization of TbFe3 by nitrogen absorption : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5733-5735 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nitrogenation process of the TbFe3 intermetallic compound was studied by heat treating the alloy between 573 and 873 K in a nitrogen atmosphere. The structural and magnetic properties of the nitrogenated samples were characterized by x-ray diffraction (XRD), Mössbauer spectroscopy, and magnetic measurements. The magnetic moments of the nitrogenated samples were found to be a function of the annealing temperature and showed a minimum for the sample heat treated at 673 K. The XRD pattern of this sample (673 K) showed that the Bragg peaks of the 1-3 phase had completely disappeared and were replaced by a broad maximum indicating a breakdown of the TbFe3 structure into an amorphous phase. The room-temperature Mössbauer spectrum of the same sample consisted almost entirely of a quadrupole-split doublet plus a small amount of α-Fe and TbFe3. This doublet split into a broad spectrum upon cooling which is typical of amorphous rare-earth–transition-metal compounds. For samples heat treated at higher temperatures, the amount of α-Fe and TbN phases gradually increased. This nitrogenation process is unlike that of R2Fe17. In this study, nitrogen atoms do not go into the interstitial sites. Instead, they create a ferromagnetic (TC≈215 K) amorphous phase of Tb, Fe, and N which is stable over a wide temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353607
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  • 5
    Electronic Resource
    Electronic Resource
    Stress effect on the magnetization of Dy in the Dy/DyFe2 eutectic : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7027-7029 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization of the alloy DyFe1.5 was studied as a function of temperature from 50 to 300 K in a range of magnetic field up to 10 kOe. Metallographic studies showed the existence of a eutectic phase containing both DyFe2 and elemental Dy embedded in the DyFe2 matrix. The presence of elemental Dy was observed in the magnetization data through a cusp in the temperature dependence of the magnetization at 178 K and an increase of the magnetization starting at 130 K and continuing to 80 K. While the first feature occurs at precisely the Néel temperature of bulk Dy, the second contrasts with the jump at the Curie temperature of 89 K observed in low fields in bulk single-crystal Dy. The more gradual increase in magnetization observed in the DyFe1.5 alloy is attributed to variations in stress to which the Dy is subjected. The temperature dependence of the magnetic moment from 80 to 130 K is modeled as arising from a collection of Dy particles of varying Curie temperatures. This variation is in turn caused by the stress distribution. Curie temperature distributions are found for a range of magnetic fields and then are extrapolated to zero field in order to eliminate the effect of field. The calculations indicate that a significant amount of the Dy remains in the helimagnetic phase down to zero temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358076
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  • 6
    Electronic Resource
    Electronic Resource
    Noncollinear phase of TbDy alloys (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5987-5989 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.346037
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  • 7
    Electronic Resource
    Electronic Resource
    Histologic and microbiologic features of biopsy samples from patients with normal and inflamed pouches (1994)
    Springer
    Diseases of the colon & rectum 37 (1994), S. 26-31 
    Details
    ISSN: 1530-0358
    Keywords: Ileal reservoir ; Kock continent ileostomy ; Pouchitis ; Ulcerative colitis ; Crohn's disease ; Familial adenomatous polyposis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract PURPOSE: This study was undertaken to assess the electron microscopic and microbiologic findings in tissue biopsy samples from patients with pouchitis and to compare them with findings in patients with normal pouches, conventional ileostomies, and normal ileum. METHODS: Tissue samples were obtained from 78 patients: 23 patients with normal pouches endoscopically and histologically (Group 1), 12 patients with endoscopic and histologic evidence of inflammation (pouchitis) (Group 2), 14 patients who had either endoscopic or histologic evidence of inflammation but not both (Group 3), 20 patients with conventional ileostomies (Group 4), and 9 patients without ileostomies from whom biopsy samples of normal ileum were obtained (Group 5). RESULTS: The mean total aerobic facultative counts in the biopsy samples from the pouchitis patients were significantly higher when compared with biopsy samples from Groups 4 and 5 ( P 〈0.05). There were no significant differences in the mean anaerobic counts among the five groups. Positive cultures were obtained in 90 percent of patients with pouches compared with 69 percent of patients with conventional ileostomies or normal ileum ( P 〈0.05). Intramural bacteria were observed on electron microscopy in biopsy specimens of 47 percent patients with pouches compared with 14 percent of patients with conventional ileostomies or normal ileum ( P 〈0.05). However, the proportion of patients with positive cultures or intramural bacteria was not increased in the pouchitis group compared with the normal pouch group. CONCLUSION: These data suggest that intramural aerobic facultative bacterial counts are elevated in patients with pouchitis and may play a role in the pathogenesis of pouchitis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02047210
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  • 8
    Electronic Resource
    Electronic Resource
    Progression of pulmonary cystic disease during ECMO (1990)
    Springer
    Pediatric radiology 20 (1990), S. 191-191 
    Details
    ISSN: 1432-1998
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Only one of the 65 ECMO patients treated at Thomas Jefferson University Hospital to date has shown progression of pulmonary parenchymal cystic change on serial portable chest radiographs while on ECMO. The radiographic and clinical findings of this unique case are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02012971
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  • 9
    Electronic Resource
    Electronic Resource
    Thin Film Ceramic Coatings via the Sol-Gel Process (1991)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 53-55 (Jan. 1991), p. 427-432 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/58/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.53-55.427.pdf
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  • 10
    Electronic Resource
    Electronic Resource
    Sol-Gel Precursor Chemistry (1991)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 53-55 (Jan. 1991), p. 445-450 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/58/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.53-55.445.pdf
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