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  • 1
    Electronic Resource
    Electronic Resource
    The effect of magnetic interaction in barium hexaferrite particles : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3812-3814 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of interactions on the magnetic relaxation of nanocrystalline hexagonal barium hexaferrite BaFe10.4Co0.8Ti0.8O19 is discussed. We had previously shown that according to the T ln(t/τ0) scaling, an enhancement of the lowest-energy barriers was detected when demagnetizing interactions were dominant. Also, the Henkel plots obtained for particles of about 10 nm of mean diameter showed that the overall interactions were demagnetizing. In the present work, we have modified the interactions by milling the particles with a nanosized SiO2 powder. Dipolar interactions are modified by breaking the particle aggregates. The observed overall interactions resulted to be also demagnetizing for the milled sample. The time dependence of the magnetization was analyzed according to two different procedures: the fluctuation field and activation volume analysis and the T ln(t/τ0) scaling. Activation volumes were found to increase with demagnetizing interactions and the leading demagnetizing mechanism appeared to shift from an individual particle mode for the unmilled sample to a collective one for the milled sample. The second approach showed larger relaxation rates at short times for the milled sample. The effective energy barrier distribution obtained from the scaling suggested that demagnetizing interactions increased in the milled sample, which led to an enhancement of the amount of the lowest-energy barriers. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364778
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic study of M-type doped barium ferrite nanocrystalline powders (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3333-3340 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the static magnetic properties of three different M-type doped barium ferrite compounds prepared by the glass crystallization method. The zero-field-cooled (ZFC) and field-cooled (FC) processes have been recorded at low field and they all show the typical features of a small particle system. The ZFC curves display a broad peak at a temperature TM, which depends on the distribution of particle volumes in the sample. Isothermal magnetization curves M(H) at several temperatures and saturation magnetization Ms as a function of temperature have been measured for the Co-Ti sample (BaFe10.4Co0.8Ti0.8O19). The dependence on temperature of the macroscopic magnetic parameters has been analyzed. The distribution of blocking temperatures is studied from the derivative of the remanent-to-saturation magnetization ratio with respect to temperature and it is fitted to a lognormal distribution, leading to a mean blocking temperature 〈TB〉=(81±40) K. The distribution of volumes of the magnetic unit is also obtained from this fitting. The dependence on temperature of the coercive field follows a Tk-law below 35 K. The value of the k exponent is discussed within the scope of two models: (i) the aligned case (k=0.5) and (ii) the random case (k=0.77).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354558
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  • 3
    Electronic Resource
    Electronic Resource
    T⋅ln(t/τ0) scaling approach and fluctuation field analysis in interacting particulate systems (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 7427-7431 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time dependence of the magnetization in samples having a different degree of interparticle interactions is analyzed. The selected compound was a nanocrystalline powder of the composition BaFe10.4Co0.8Ti0.8O19 with and without an admixture of nanosized SiO2 particles. Two different approaches were considered for the analysis of the thermally activated demagnetization: the T⋅ln(t/τ0) scaling of the thermomagnetic relaxation in zero applied field, and the classical fluctuation field and activation volume analysis. The energy barrier distribution obtained from the former approach shows that the occurrence of larger demagnetizing interactions leads to a relative enhancement of the lowest energy barriers with respect to the largest barriers. Activation volumes are found to increase with demagnetizing interactions and the leading demagnetizing mechanism appears to shift from an individual particle mode (coherent or nucleation) to a collective one. Both analyses are suggested to be taken into account in order to ascertain the influence of interactions on the magnetic properties of nanocrystalline particles.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365442
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic properties of nanocrystalline barium hexaferrite powders: anisotropy field and interaction effects
    Amsterdam : Elsevier
    Journal of Magnetism and Magnetic Materials 127 (1993), S. 229-232 
    Details
    ISSN: 0304-8853
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0304-8853(93)90220-V
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