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  • 1
    Electronic Resource
    Electronic Resource
    Effect of cobalt-ferrite epitaxial layer on the coercivity of ZnFe-ferrite particles (abstract) (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3898-3898 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Zn0.2Fe2.8O4 particles were prepared and coated with different amounts of cobalt-ferrite. The coercivity increases with increasing cobalt-ferrite coating. In the low Co-ferrite coating regime, the increase is induced by an enhanced anisotropy of the interface layer, while in the high coating regime, it is due to the Co-ferrite surface layer. The full depth of the interface layer was found to be approximately 8 A(ring), and the temperature dependence of the change in coercivity in both low and high Co-ferrite coating regimes was discussed. Mechanisms leading to a greatly increased coercivity of acicular Co-γ-Fe2O3 were also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338602
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic properties of fine iron particles (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3314-3316 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Iron particles were prepared by a gas evaporation method in a nitrogen atmosphere. The particle size, shape, and magnetic properties were influenced by the nitrogen pressure. Particles prepared by this method were relatively stable in air and were not seriously oxidized. The recoilless fraction is low for the oxide layer, so that it cannot be detected at room temperature by Mössbauer spectrum. A superparamagnetic peak associated with the oxide microcrystal layer did not occur in the Mössbauer spectra due to the action of the magnetic field from the iron core and the interaction between iron particles and the low Debye temperature. From the electron micrography, the magnetic reversal process seems to be determined by a chain-of-spheres mechanism but Hc∼T curve cannot coincide with the Ms∼T curve at low temperatures. An increase of Hc may be associated with magnetic anisotropy. It is found that the magnetization versus temperature shows an anomalous increase in M(T) at higher T. We think that this means that the surface oxide layer was not magnetized to saturation even under 40 kOe at 5.5 K as the surface anisotropy is rather large.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338893
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties of ultrafine nickel particles : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5903-5905 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrafine nickel particles have intriguing physical and chemical properties, which are interesting both in fundamental and applied research. The size of the particle was controlled by gas pressure. X-ray diffraction studies showed that fine Ni particles have fcc crystal structure and are coated with thin Ni oxide on the surface. Electron micrographs showed a spherical particle shape, forming a long chain. Size dependence of magnetic properties were studied. The specific magnetic moment drastically decreases when reducing the diameter d of particles 〈15 nm. The coercivity Hc also approaches zero when d is about 15 nm. Therefore, we can suppose that the critical size for superparamagnetism at room temperature is about 15 nm. According to the superparamagnetic formula KV=25 kT, the value of the magnetic anisotropy constant can be determined, K = −5.8 × 105 (erg/cc). It is found to be larger than bulk Ni [K=−3.4–5.1 × 104 (erg/cc)], the same as Fe particles. The maximum of coercivity at room temperature is about 250 Oe, that is less than the theory value for the coherent rotation model, Hc = 4 K/3Ms=1600 Oe. The mechanism of reversal magnetization can be understood by the sphere chain model. The critical diameter of the single domain is about 65 nm. Curie temperature Tc obviously decreases for 9-nm average diameter particles rather than bulk. It may be in connection with the lattice contraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350101
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Mn Substitution on the Structure and Microwave Properties of Nd-Fe-B Nanocomposites (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 561-565 (Oct. 2007), p. 1105-1108 
    Details
    ISSN: 1662-9752
    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
    Notes: The influence of Mn content on the structure and magnetic permeability ofNd3Fe68-xMnxCo18B11 (x = 0, 1, 2) amorphous soft magnetic alloys was studied. The ribbons wereprepared by melt-spining. The permittivity–frequency and permeability–frequency properties weredetermined in the microwave frequency regime of 2-18 GHz by vector network analysis. XRD spectrashowed that only α-Fe diffraction peak was observed in the as-spun alloy. It is found that the acquiredcomplex permittivity and permeability values match the microwave frequency when the 1at% Mncontent doped. The results suggest a new design of microwave absorbers based on electromagneticwave absorbing materials
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/17/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.561-565.1105.pdf
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