Superparamagnetic particles dynamic susceptibilities

III. Low-Frequency Nonlinear Susceptibilities of Superparamagnetic Particles in Solid Matrices A. Linear and Cubic Dynamic Susceptibilities Numerical Solutions... 

To summarize this part of the chapter, we have constructed a consistent theory of linear and cubic dynamic susceptibilities of a noninteracting superparamagnetic system with uniaxial particle anisotropy. The scheme developed was specified for consideration of the assemblies with random axis distribution but may be easily extended for any other type of the orientational order imposed on the particle anisotropy axes. A proposed simple approximation is shown to be capable of successful replacement of the results of numerical calculations. 

The study that we describe below was inspired by our work on fitting the dynamic susceptibilities measurements for real assemblies of fine particles. Those data typically describe polydisperse systems in the low-frequency bandwidth a>/2% = 1 — 103 Hz. As To 10 s or smaller, then, using formula (4.132) for estimations, one concludes that the frequency interval mentioned becomes a dispersion range for the interwell (superparamagnetic) mode at coto< ct > 1, that is, a > 10. For temperatures up to 300 K, this condition holds for quite a number of nanomagnetic systems. 

Garcia-Palacios JL, Lazaro FJ (1997) Anisotropy effects on the nonlinear magnetic susceptibilities of superparamagnetic particles. Phys Rev B 55 1006-1010 Garcia-Palacios JL, Svedlindh P (2000) Large nonlinear dynamical response of superparamagnets Interplay between precession and thermoactivation in the stochastic Landau-Lifshitz equation. Phys Rev Lett 85 3724-3727... 

Raikher YL, Stepanov VI (1997) Linear and cubic dynamic susceptibilities of superparamagnetic fine particles. Phys Rev B 55 15005-15017... 

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