Frequency-dependent effective permeability tensor of unsaturated polycrystalline ferrites

Abstract

Frequency-dependent permeability tensor for unsaturated polycrystalline ferrites is derived through an effective medium approximation that combines both domain-wall motion and rotation of domains in a single consistent scattering framework. Thus derived permeability tensor is averaged on a distribution function of the free energy that encodes paramagnetic states for anhysteretic loops. The initial permeability is computed and frequency spectra are given by varying macroscopic remanent field.

A functional calculus for the magnetization dynamics

“…We thus assume that Eqs. (17,18,19,20,29) and (30) give enough information for the simulation of the average magnetization dynamics, using the Gaussian closure.…”

“…Equations (37) and (38) have to be injected into Eqs. (17,18,19,20,29) and ( 30) respectively. Because of the form these equations assume, they were called dynamical Landau-Lifshitz-Bloch (d-LLB) equations 11,52 and reveal, for both the first and second moments, a longitudinal contribution, proportional to the amplitude of the noise, to the damping of the average magnetization.…”

“…While at the level of a single spin, this approach can only describe transverse, but not longitudinal, damping effects 14,15 , it has been shown [16][17][18] that an appropriate averaging procedure over the bath can, in fact, describe longitudinal damping effects, that are typical in finite size magnetic grains. Thus, it may be a good starting point for developing models that incorporate the corrections to the mean field behavior of a single domain, beyond the effective medium approximation 19,20 . Damping is responsible for the transfert of spin angular momentum from the magnetization to the environment and allows conversely energy to be pumped from the environment to the magnetization.…”

Electromagnetic Filters Based on a Single Negative Photonic Comb-Like Structure

“…For example, many plasmas (such as noble metals including gold and silver in infrared and visible regions) which exhibit the electric negative characteristic or gyrotropic (gyromagnetic) materials (such as ferromagnetic materials) show magnetic negative characteristic. Therefore, particular efforts have been purposed in exploring how some of the exciting phenomena and applications predicted and studied in (LHMs) can be transferred into SNGs [19][20][21]. In general, there are two types of SNG materials.…”

Colored-Noise Magnetization Dynamics: From Weakly to Strongly Correlated Noise

“…The study of the effects of thermal fluctuations on the magnetization dynamics, by way of stochastic simulations, is a topic that has received much attention [1], [2]. What has also been the subject of numerous studies, in the field of coarsegrained simulations [3], is the development of multiscale models, able to simulate the average magnetic behaviour of a spin assembly under thermal stresses [4], [5]. But in both contexts, the coupling between the thermal bath and the spin assembly has mainly been taken into account within the framework of the white-noise limit, and few studies [6], [7] have considered the effects of a finite auto-correlation time for the response of the thermal bath, i.e.…”