Exact analytic formula for the correlation time of a single-domain ferromagnetic particle

Coffey, W. T.; Crothers, D S F; Kalmykov, Yuri P.; Massawe, Estomih S.; Waldron, J T

doi:10.1103/physreve.49.1869

Cited by 116 publications

(58 citation statements)

References 22 publications

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“…One method [19] implies a direct integration of the Fokker-Planck equation. Another method [20] involves solving three-term recurrence relations for the statistical moments of W . The emerging solution for τ int can be expressed in a finite form in terms of hypergeometric (Kummer's) functions.…”

Section: Asymptotic Integral Timementioning

confidence: 99%

Linear and nonlinear superparamagnetic relaxation at high anisotropy barriers

Raǐkher

Stepanov

2002

Phys. Rev. B

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The micromagnetic Fokker-Planck equation is solved for a uniaxial particle in the low-temperature limit. Asymptotic series in the parameter that is the inverse barrier height-to-temperature ratio are derived. With the aid of these series, the expressions for the superparamagnetic relaxation time and the odd-order dynamic susceptibilities are presented. The obtained formulas are both quite compact and practically exact in the low (with respect to FMR) frequency range that is proved by comparison with the numerically-exact solution of the micromagnetic equation. The susceptibilities formulas contain angular dependencies that allow to consider textured as well as randomly oriented particle assemblies. Our results advance the previous two-level model for nonlinear superparamagnetic relaxation.

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Section: Asymptotic Integral Timementioning

confidence: 99%

Linear and nonlinear superparamagnetic relaxation at high anisotropy barriers

Raǐkher

Stepanov

2002

Phys. Rev. B

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“…19 The anisotropy favors some particular orientations of the magnetic moment, two opposite to each other in the simplest case of uniaxial anisotropy, which are separated by activation energy barriers U . As the temperature decreases, the number of thermal phonons of energy equal or larger than U decreases, thus leading to an exponential increase of the time τ needed to reverse the magnetic moment of a particle [19][20][21] …”

Section: A Superparamagnetic Blockingmentioning

confidence: 99%

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

et al. 2002

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We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.4 nm (25 to 7500 atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared to previous structural characterizations. The distribution of activation energies was independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant K ef f . We find that K ef f is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal is shown to proceed classically down to the lowest temperature investigated (1.8 K).

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“…10 At present this approach is widely used for studying magnetic properties of nanoparticle systems at finite temperatures, including magnetic relaxation. [10][11][12][13][14][15][16] In this paper, we use the deterministic and the stochastic Landau-Lifshitz equations to study some effects induced by the rotating magnetic field in systems of purely deterministic and weakly superparamagnetic nanoparticles. More precisely, we are interested in the effects that arise from the different dynamical states of the up and down magnetic moments.…”

Section: Introductionmentioning

confidence: 99%

Dynamical and thermal effects in nanoparticle systems driven by a rotating magnetic field

et al. 2006

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We study dynamical and thermal effects that are induced in nanoparticle systems by a rotating magnetic field. Using the deterministic Landau-Lifshitz equation and appropriate rotating coordinate systems, we derive the equations that characterize the steady-state precession of the nanoparticle magnetic moments and study a stability criterion for this type of motion. On this basis, we describe ͑i͒ the influence of the rotating field on the stability of the small-angle precession, ͑ii͒ the dynamical magnetization of nanoparticle systems, and ͑iii͒ the switching of the magnetic moments under the action of the rotating field. Using the backward Fokker-Planck equation, which corresponds to the stochastic Landau-Lifshitz equation, we develop a method for calculating the mean residence times that the driven magnetic moments dwell in the up and down states. Within this framework, the features of the induced magnetization and magnetic relaxation are elucidated.

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Exact analytic formula for the correlation time of a single-domain ferromagnetic particle

Cited by 116 publications

References 22 publications

Linear and nonlinear superparamagnetic relaxation at high anisotropy barriers

Linear and nonlinear superparamagnetic relaxation at high anisotropy barriers

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

Dynamical and thermal effects in nanoparticle systems driven by a rotating magnetic field

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