Browsing by Author "Crothers, D. S. F."

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    Exact Analytic Formula for the Correlation Time of a Single-Domain Ferromagnetic Particle
    (1994) Coffey, William T.; Crothers, D. S. F.; Kalmykov, Yuri P.; Massawe, Estomih S.; Waldron, J. T.
    Exact solutions for the longitudinal relaxation time T∥ and the complex susceptibility χ∥(ω) of a thermally agitated single-domain ferromagnetic particle are presented for the simple uniaxial potential of the crystalline anisotropy considered by Brown [Phys. Rev. 130, 1677 (1963)]. This is accomplished by expanding the spatial part of the distribution function of magnetic-moment orientations on the unit sphere in the Fokker-Planck equation in Legendre polynomials. This leads to the three-term recurrence relation for the Laplace transform of the decay functions. The recurrence relation may be solved exactly in terms of continued fractions. The zero-frequency limit of the solution yields an analytic formula for T∥ as a series of confluent hypergeometric (Kummer) functions which is easily tabulated for all potential-barrier heights. The asymptotic formula for T∥ of Brown is recovered in the limit of high barriers. On conversion of the exact solution for T∥ to integral form, it is shown using the method of steepest descents that an asymptotic correction to Brown’s high-barrier result is necessary. The inadequacy of the effective-eigenvalue method as applied to the calculation of T∥ is discussed.
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    Exact Analytic Formula for the Correlation Times for Single Domain Ferromagnetic Particles.
    (Elsevier, 1993) Coffey, William T.; Crothers, D. S. F.; Kalmykov, Yuri P.; Massawe, Estomih S.; Waldron, J. T.
    Exact solutions for the longitudinal relaxation time T∥ and the complex susceptibility χ∥(ω) of a thermally agitated single domain ferromagnetic particle are presented for the simple uniaxial (Maier-Saupe) potential of the crystalline anisotropy considered by Brown [Phys. Rev. 130 (1963) 1677].