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  • 1
    Electronic Resource
    Electronic Resource
    The structure–property relationships in M-type hexaferrites: Hyperfine interactions and bulk magnetic properties : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6295-6297 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 57Fe Mössbauer spectroscopic measurements have been made at 296 K on single crystals of MFe12O19 (M=Ba, Sr, Pb) oriented parallel and perpendicular to the c axis, permitting the establishment of the systematics of the static and dynamical aspects of the hyperfine interactions, and their relationship to crystal/chemical structures for the five Fe3+ sublattices, and to the bulk magnetic properties. With the exception of the electric quadrupole interaction at the 2b site, and the dependence of the 2b intensity on the crystal orientation, the magnitude of the hyperfine interactions of a given Fe3+ site exhibits only small variations among the different hexaferrites. The magnitude of the quadrupole interaction at the 2b site varies by more than 10%, with the 2b site in PbFe12O19 exhibiting the smallest value. The relative intensity of the 2b subspectrum varies markedly among the three hexaferrites for observations parallel and perpendicular to the c axis. Although all display the expected anisotropy resulting from the libration of the 2b Fe3+ parallel to the c axis, the anisotropy is considerably larger for PbFe12O19 than for BaFe12O19 or SrFe12O19. It is remarkable that the bulk magnetic anisotropy follows the same order as the anisotropy in the dynamical displacement and crystalline electric field of the 2b site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352675
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  • 2
    Electronic Resource
    Electronic Resource
    The 57Fe Mössbauer spectra of oriented single-crystal and powder PbFe12O19 (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6231-6231 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The recent determination of the crystal structure of PbFe12O19 by means of single-crystal x-ray diffraction has made it possible to carry out a definitive and comparative analysis of the structure-property relationship of PbFe12O19, SrFe12O19, and BaFe12O19. We have therefore performed 57Fe Mössbauer measurements on oriented, single-crystal, and powder samples of PbFe12O19 at 298 K. For a single-crystal oriented parallel to the c axis, five distinct patterns are observed. The hyperfine fields, isomer shifts, and quadrupole interactions are as follows: 12k: Heff=413 kOe; δ=0.33 mm s−1; Δ=0.35 mm s−1; 4f1: 487 kOe; 0.24 mm s−1; 0.13 mm s−1; 4f2: 514 kOe; 0.39 mm s−1; 0.29 mm s−1; 2a: 496 kOe; 0.30 mm s−1; 0.11 mm s−1; 2b: 399 kOe; 0.30 mm s−1; 2.00 mm s−1. The relative magnitude of each of these parameters is in good agreement with and exhibits the same trend observed for high-purity SrFe12O19. The relative intensity of the 2b pattern for the crystal oriented parallel to the c axis is 8.2%, which approaches its theoretical value; of the total number of iron ions in the structure, 8.33% of them occupy the 2b site. The value for the polycrystalline sample is only 5.4% of the total intensity. However, for a single crystal oriented perpendicular to the c axis, the 2b pattern exhibits a negligible intensity within the experimental error. This result confirms the dynamic disorder in the position of the 2b iron ions and suggests a stronger anisotropy for the case of PbFe12O19 than for SrFe12O19 and BaFe12O19. Even though the trend in hyperfine parameters at 298 K is similar to Sr, Ba, and Pb hexaferrites, PbFe12O19 exhibits hyperfine fields that are consistently lower than those of the Ba and Sr analogues. This result is discussed in terms of the Curie temperatures, magnetic exchange interactions, and structural parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348818
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties, compositions, and microstructures of high-energy product strontium hexaferrites (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4601-4603 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Commercial, high-energy product strontium hexaferrites have been characterized in terms of their chemical compositions, microstructures, and bulk and submicroscopic magnetic properties. Compared to earlier permanent magnetic hexaferrites, these materials have a unique composition, containing no elements other than Sr and Fe at appreciable concentrations; dopants for nucleation and microstructure control are apparently absent. The microstructures indicate that, in some cases, the materials may be fully reacted prior to forming the final ceramic bodies. The compositions are variable and tend to be nonstoichiometric despite the absence of impurity elements. These deviations from stoichiometry are reflected in the Mössbauer spectra which indicate that further refinements can be made in the definition of the different magnetic sublattices. These refinements may lead to further advances in the magnetic properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344852
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  • 4
    Electronic Resource
    Electronic Resource
    57Fe Mössbauer spectroscopic investigation of complex magnetic structures in Ga, Sc, and In substituted M-type hexagonal ferrites (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5229-5230 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Investigation of preliminary evidence that Ga, Sc, and In influence the bulk and dynamic magnetic properties of hexagonal ferrites by means other than those supported in existing models has been undertaken. In SrFe12−xMxO19 (M=Ga, In) and BaFe12−xScxO19, the predominant 12k sublattice exhibits a remarkable splitting into two distinct subpatterns, 12k1 and 12k2: At x=0.3, hyperfine fields, Heff for 12k1 are 411, 408, and 405 kOe, respectively, and for 12k2 are 358, 339, and 311 kOe, respectively. The 12k1 hyperfine field values are virtually unchanged from that of the pure hexagonal ferrites and are independent of substitution level. Contrastingly, the abruptness of the drop in the 12k2 hyperfine field and its dependence on the nature of the substituting cation are remarkable. The relative intensity of the 12k2 component correlates with the concentration of nonmagnetic species on the 2b and 4f2 sites and with the magnetic anisotropy. Scandium seems to have a more profound influence on the magnetic structure and interactions than indium or gallium. Further, at technically significant substitution levels, Heff of the different sublattices exhibit broad and overlapping distributions of values far removed from their distinctiveness in the pure hexaferrites. Thus, the net magnetization of Ga, Sc, and In-doped hexaferrites results from a complex interplay of magnetic dilution on the 2b site, enhancement of the magnetization through substitutions on the 4f2 site, and a complex influence from the substitution-induced 12k2 sublattice. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369952
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  • 5
    Electronic Resource
    Electronic Resource
    Order-disorder and magnetic exchange interactions in substituted strontium hexaferrite SrAxFe12−xO19(A=Ga, In) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6643-6645 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The unusual magnetic behavior of the 12k site in SrGaxFe12−xO19 (0.3≤x≤6.0) and SrInxFe12−xO19 (0.3≤x≤1.4) has been investigated by means of 57Fe Mössbauer spectroscopy at 298 K. The bifurcation of the 12k Mössbauer subspectrum into 12k1 and 12k2 components of widely differing intensities has been confirmed for both Ga3+ and In3+. The bifurcation is apparent at x values as low as 0.3, and the less intense 12k2 pattern corresponds to an abrupt drop in the hyperfine magnetic field Heff, of 50 and 75 kOe for Ga3+ and In3+, respectively. Heff for the more intense 12k1 pattern is virtually unchanged from that of pure SrFe12O19 for x values as high as 1.0. Room-temperature Mössbauer spectra confirm that the Ga3+ and In3+ ions preferentially occupy the 4f2 octahedral site. There are indications, however, that the dopants also enter the 2b trigonal-bipyramidal site. The change in Heff at the 12k sites indicates that complex and competing exchange interactions are present, and that the splitting of the 12k magnetic hyperfine spectrum is not due simply to random disruptions of the exchange interactions. The intensities of the 12k1 and 12k2 subspectra have been used to model the exchange interactions at the 12k site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356881
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  • 6
    Electronic Resource
    Electronic Resource
    Structure-property relationships in the R-type hexaferrites: Cation distributions and magnetic susceptibilities of MX2Fe4O11 (1994)
    Springer
    Hyperfine interactions 94 (1994), S. 2039-2044 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The strong, and heretofore unexplained, dependence of the magnetic properties of the R-type hexaferrites MX2Fe4O11 on heat treatment has been investigated by means of57Fe and119Sn Mössbauer spectroscopy at 297 K.57Fe Mössbauer spectra of samples of BaTi2Fe4O11, BaSn2Fe4O11, and SrSn2Fe4O11, annealed at several temperatures consist of three partially resolved quadrupole doublet patterns. The pattern with the very large quadrupole splitting, i.e. 1.3 mm s−1 ≤ δE Q ≤ 1.7 mm s−1, is readily assigned to the trigonal bipyramidal site, and exhibits no dependence of its parameters, including the relative intensity, on heat treatment. The remaining two patterns are assigned to Fe3+ ions on octahedral sites, and exhibit relative intensities that are strongly dependent on heat treatment. The119Sn spectrum of BaSn2Fe4O11 is a broad, apparently single line that, with the exception of verifying the presence of tin as Sn4+, provides little insight into the details of the structure. The distributions of the cations over all the lattice sites have been deduced from the Mössbauer spectra and compared with the magnetic susceptibility data. It is concluded that the cation distributions of the Sn-containing phase are not strongly dependent on heat treatment, and the magnetic properties exhibit a similar insensitivity to heat treatment. The Ti analogs exhibit a strong dependence of cation distribution on heat treatment, which is reflected in widely varying magnetic ordering temperatures, a variation that is confirmed by the incipient magnetic hyperfine splitting despite the strong magnetic frustration in the R-type hexaferrites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02063737
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  • 7
    Electronic Resource
    Electronic Resource
    57Fe Mössbauer investigations of manganese-containing spinels (1994)
    Springer
    Hyperfine interactions 90 (1994), S. 353-358 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Cation distributions and related order-disorder phenomena in the naturally occurring Mn-spinels: iwakiite, galaxite and franklinite, have been investigated by means of57Fe Mössbauer spectroscopy. Previous measurements on an iwakiite sample indicated the existence of Mn-rich and Mn-poor regions. This interpretation has been confirmed in this investigation by further measurements on annealed iwakiite samples. The57Fe Mössbauer spectrum of galaxite from Bald Knob, NC, is a well-resolved quadrupole doublet and indicates the presence of a single crystallographic Fe3+ species. A “galaxite” sample from Thailand exhibited a complex spectrum of Fe2+ and Fe3+ quadrupole doublets: This sample has been misidentified and should be regarded as a member of the (Mg, Fe)(Al, Fe)2O4 series. The57Fe hyperfine parameters of a rare franklinite from Längban, Sweden, are very close to those for synthetic zinc ferrite, confirming electron microprobe results of an unusually high zinc content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02069138
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