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  • 1990-1994  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Phase changes in plasma-sprayed zinc-nickel ferrite : 35TH ANNUAL CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS San Diego, California (USA) 29 Oct−1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5355-5357 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic and crystalline properties of a plasma-sprayed coating of the microwave absorbing zinc-nickel ferrite, (Zn0.41Ni0.59 )Fe2O4 have been studied at 300 K using the Mössbauer effect and x-ray diffraction (XRD). Both techniques indicate that the plasma-sprayed material separated into two phases. The first is a nickel-rich phase with magnetic fields of 47.5 and 44.5 T at the tetrahedral and octahedral sites, respectively. The second is a zinc-rich phase, zinc meta-ferrite, having a small magnetic field of 4.2 T. The quadrupole splitting of this second phase is ΔE=0.34 mm s−1, which is the same as in pure nonmagnetic zinc ferrite. XRD analysis shows that the zinc-rich phase remains cubic with a0= 8.389 A(ring) and the zinc meta-ferrite phase is tetragonal with the same lattice parameters as the cubic phase except for one elongated axis given by c0 =8.488 A(ring). This is much larger than the spacing for any of the series of zinc-nickel ferrites. The isomer shift of the zinc meta-ferrite is 0.710 mm s−1, which indicates that a large fraction of Fe3+ was reduced during the spraying process. Annealing the sprayed coating at temperatures less than 400 °C converted the zinc meta-ferrite into a magnetic phase that now exhibits magnetic fields close to those in the nickel-rich phase. However, the large isomer shift remains, indicating that the ferrous iron is still present. XRD shows that the phase is now cubic. Annealing up to 650 °C gradually oxidized all of the Fe2+ in the material and restored the magnetic and crystalline properties of the plasma-sprayed coating to very close to those of the unsprayed ferrite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348027
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic-field distributions in zinc-nickel ferrite : 35TH ANNUAL CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS San Diego, California (USA) 29 Oct−1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5352-5354 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Mössbauer effect has been used to study the microscopic magnetic properties of the cubic microwave ferrite (Zn0.41Ni0.59)Fe2O4 at 300 K. The magnetically split spectrum is broad and unresolved due to the overlap of the hyperfine magnetic fields at the tetrahedral and octahedral sites. This is caused by a distribution of magnetic fields at each site. The distribution is especially large and asymmetric at the octahedral site and is due to the fact that the iron atoms at this site are influenced by the presence of both iron and zinc at the tetrahedral site. The octahedral site is more sensitive to changes in the number of zinc neighbors than is the tetrahedral site. Assuming a random distribution of the zinc at the tetrahedral site, and knowing the fraction of zinc in the ferrite, the binomial distribution has been used to calculate the expected magnetic-field distribution at the octahedral site as a function of the number of zinc neighbors. These figures have been compared with the magnetic-field distribution profile determined from the fit to the Mössbauer spectrum. Sufficiently good agreement has been found to allow us to isolate the magnetic-field contribution due to most of the different numbers, between zero and six, of neighboring zinc atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348026
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic hyperfine interactions in GdAl3 (1990)
    Springer
    Hyperfine interactions 54 (1990), S. 689-694 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the magnetic hyperfine interactions in GdAl3 using155Gd Mössbauer spectroscopy between the temperatures of 4K and 90K. Previous studies on GdAl3 have shown that antiferromagnetic ordering occurs at 18K, and that a fit of the susceptibility to 1/(T-θp) yields a θp value of −89K. The large ratio of θp to TN is indicative of magnetic frustration between competing ferro-and antiferromagnetic interactions, which may be due to a combination of the oscillatory nature of the RKKY interaction and the geometry of the hexagonal lattice. Our studies show that the saturation magnetic hyperfine field at the Gd site is −24.0 T, with the moments lying in the basal plane. The efg at the gadolinium site is 2.55(1)×1017V cm−2 which is considerably larger than the value predicted by a point charge calculation. This difference may indicate that there is a conduction electron contribution. A helical magnetic structure has been calculated from RKKY theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396113
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  • 4
    Electronic Resource
    Electronic Resource
    The microstructural properties of highly nitrogenated iron and iron-aluminum powders (1994)
    Springer
    Hyperfine interactions 92 (1994), S. 959-964 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study has been made of highly nitrogenated pure iron and iron-aluminum alloy powder containing 2 wt.% Al (Fe-2Al) using Mössbauer spectroscopy and X-ray diffraction. The samples were prepared by high-temperature, high-pressure diffusion of nitrogen. They were prepared in a hot-isostatic-pressure (HIP) furnace at 1000 °C at nitrogen pressures up to 200 MPa. The alloy powders contained up to 8 at.% nitrogen as determined by vacuum fusion analysis. XRD analysis indicates that for the pure iron powders, the lattice spacing remained independent of nitrogen concentration, but that for the Fe-2Al powders, it decreased with increasing nitrogen concentration. Mössbauer analysis showed that for the pure iron powders, most of the nitrogen was associated with the formation of the iron nitride Fe4N. For the alloy powders containing less than 5 at.% nitrogen, all of the nitrogen was contained interstitially. The presence of nitrogen completely eliminated the conduction-electron spin-density oscillations observed in many ferromagnetic alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02065719
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  • 5
    Electronic Resource
    Electronic Resource
    A high temperature Mössbauer effect study of iron-doped YBa2Cu3O7 superconductor (1994)
    Springer
    Hyperfine interactions 93 (1994), S. 1627-1633 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Superconducting YBa2Cu2.955Fe0.045O7 has been studied at temperatures between 300 and 1000 K. Spectra were recorded on a sample which was sealed as a pellet pressed with boron nitride. An atmosphere of oxygen was maintained in the sample region at all times. At temperatures up to 900 K, we observed the four iron sites A, (Cu(1) chain-site; square planar oxygen coordination with O(5) vacancy on thea-axis), B, (Cu(2) plane-site; square pyramidal oxygen coordination), C, (Cu(1) chain-site; square pyramidal oxygen coordination with O(5) site occupied) and D, (Cu(1) chain-site; quasi-tetrahedral oxygen coordination with O(4) vacancy along theb-axis). At temperatures up to 700 K, the relative area of the B and C sites remained nearly constant as the temperature was increased. However, the area of the A site decreased while, the D site area increased with increasing temperature. At all times, the total area of sites A and D remained constant, thereby indicating the possibility of oxygen atom hopping in thea-b plane. The quadrupole splitting of each site, except the B site, decreased linearly with increasing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02072919
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  • 6
    Electronic Resource
    Electronic Resource
    Zinc-iron phases formed on galvannealed steel (1990)
    Springer
    Hyperfine interactions 54 (1990), S. 781-785 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer spectroscopy has been used to identify the zinc-iron intermetallic phases present in the coating of three galvannealed steels, two of which were produced on commercial galvanizing lines and one in the laboratory. Both CEMS and XMS have been used in order to determine the depth dependence of each phase. Three main zinc-iron phases have been identified with the proportion of each dependent on the preparation conditions. In the commercially produced coatings, CEMS, probing near the top of the coating, indicates that the zinc rich χ-FeZn13 and δ-FeZn10 alloys are present. XMS indicates the presence of some Π-Fe3Zn10 closer to the steel. In contrast, the laboratory produced sample contains nearly pure χ-FeZn13 through the entire coating thickness. Subphases of the delta and gamma alloys were also identified. These subphases appear to be mixed with a preference for the higher zinc subphase of each to form closer to the surface of the coating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396128
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  • 7
    Electronic Resource
    Electronic Resource
    Mössbauer effect and XRD studies of iron-zinc binary alloys (1994)
    Springer
    Hyperfine interactions 94 (1994), S. 2309-2315 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer spectroscopy and XRD were employed to characterize the microstructural properties of iron-zinc binary alloys between 0–31 at.% Fe. Samples were prepared with accuracies of ±0.5 at.% Fe, and the Mössbauer and lattice parameters were monitored as a function of iron concentration across each phase. Two iron sites were observed in the Γ phase (18–31 at.% Fe), whose occupancies and isomer shifts varied continuously with iron content. However, the quadrupole splitting of each site remained constant. Within the Γ1 phase (19–24 at.% Fe), three iron sites were observed whose isomer shifts and quadrupole splittings remained constant, while their occupancies varied with iron concentration. For the first time, a third iron site was observed in the δ phase (8–13 at.% Fe), whose occupancy increases with iron content. Also, the site occupancies of the two other δ sites appear to remain constant, while other Mössbauer parameters vary continuously with iron content. Analysis of the ζ phase (6–7 at.% Fe) showed the presence of one iron site, whose parameters were not observed to change due to the small variance in iron concentration. XRD studies indicate the lattice parameters across the Γ and δ phases vary continuously with iron concentration. Moreover, a better understanding of these phases, as formed in galvanneal steel coatings, was obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02063780
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