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This paper describes a theoretical approach to calculate the permeability tensor of polycrystalline ferrites in various magnetization states, from the completely demagnetized state to saturation. Demagnetizing dynamic fields related to the magnetic domain and grain shapes are introduced in the initial equations to describe the interactions between domains in a grain and between grains. In this paper, we focus on the calculation of the initial permeability of polycrystalline ferrites. Results obtained from the model are compared in a completely demagnetized state to those given by the well-known Schloemann model and to experiments. In all the models given in the literature, an unusually high value of the damping factor must be introduced into the calculations to correctly describe the low-field loss region. Values of the damping factor comparable to those calculated from the measured resonance linewidth of ferrites permit the prediction of the spreading of the magnetic losses as a function of frequency experimentally observed at low bias fields and especially in the demagnetized state. [ABSTRACT FROM AUTHOR]

The purpose of this article is to bring out the nonreciprocity of ferrimagnetic powder loaded composites. We first describe their technology of preparation. Then we briefly recall the principle of the broadband measurement method used to determine the permeability tensor components of magnetized materials. Our experimental results performed at X-band frequencies (8-12 GHz) on two different ferrimagnetic loaded composite samples are presented and discussed. We finally show that for each material under test, the off-diagonal component κ of the permeability tensor, which is at the origin of the nonreciprocal effect, is of a magnitude comparable to the magnitude observed in bulk ferrites. This result proves that powders technology can be used to realize composite materials for nonreciprocal microwave applications. [ABSTRACT FROM AUTHOR]

We describe a theoretical approach for determining the permeability tensor of polycrystalline ferrites regardless of their magnetization state. To take into account both the demagnetizing dynamic fields related to the magnetic domain and grain shapes and the magnetic interactions between adjoining domains and between adjoining grains, we transform the classical Landau-Lifschitz-Gilbert equation into a coupled two-equation system. We introduce statistical distribution laws for both the domain and grain demagnetizing coefficients into the calculation to take the domain and grain shape diversity into account and derive static vectorial quantities such as the internal magnetic dc field and magnetization in each domain that depends on the applied dc magnetic field from the Stoner-Wohlfarth hysteresis model. We compare results with those for existing models for various magnetized states. Then we apply the model to predict the permeability tensor behavior of barium hexaferrite thin film, especially in the remanent state, which is of great interest for the design of self-biased Y-junction circulators in the millimeter-wave range. [ABSTRACT FROM AUTHOR]

This paper describes a mathematical model enabling the calculation of the effective permeability tensor of heterogeneous magnetic materials set in various magnetization states. The theoretical approach we propose permits to predict the microwave behavior of unsaturated magnetic loaded composites as well as those of unsaturated polycrystalline ferrites. The model gives all the complex components of the permeability tensor in a single calculation phase whatever the magnetization state of the material is. This is useful for the computer-aided design of microwave magnetic devices. The calculation of the effective permeability tensor is carded out from a limited number of parameters: saturation magnetization, anisotropy field, damping factor, external dc field strength, concentration, and shape of the magnetic particles or domains. The model is predictive in the way that the magnetization state of the material is determined from the strength of the external dc magnetic field applied on the material. [ABSTRACT FROM AUTHOR]