Measurement of the permeability tensor in nanophases of granular metal oxides and field-induced magnetic anisotropy

Abstract

We have investigated the composition and frequency dependence of the permeability tensor in heterostructures composed of metal oxides nanoparticulate powders. Samples consist of grains of the magnetic phase (␥-Fe 2 O 3 ) homogeneously dispersed in a nonmagnetic insulating background ͑ZnO͒. A measurement capability has been used to investigate the permeability tensor components of the ferrimagnetic samples under an externaly magnetic field, as a function of composition. The samples exhibit a previously unobserved fielddependent anisotropic contribution to the permeability tensor. The gyromagnetic resonance frequency decreases with Fe 2 O 3 content and increases with applied magnetic field. The frequency-dependent response in the microwave frequency range can be fit reasonably well using a single parameter whose value is consistent with the determination from a ferromagnetic resonance experiment and can be rationalized by means of a recently developed coarse-grained multiscale model. The model is based on multiscale averaging techniques and takes into account magnetostatic intergranular interactions via a mean-field approximation. These observations are aimed at developing a more realistic description of magnetic nanophases that takes into account details of the microstructure and provide salient input to micromagnetic simulations.

High-frequency behavior of magnetic composites

“…Although non-reciprocal properties are of great importance for many applications, such as circulators, isolators, tunable filters, these are beyond the scope of this paper, which considers particles that are not subjected to external magnetic bias and have the size large enough to be non-saturated, i.e., multi-domain. An interested reader is addressed to papers [10][11][12] and references therein.…”

Spin wave spectroscopy and microwave losses in granular two-phase magnetic nanocomposites

“…4,21,22 Enhanced electromagnetic properties at microwave frequencies have recently been achieved with Ni/ ␥-Fe 2 O 3 NCs. [23][24][25][26][27][28] When a͒ Author to whom correspondence should be addressed; also at Département de Physique, Université de Bretagne Occidentale; electronic mail: brosseau@univ-brest.fr compared to the zero-field case, the field measurements of the permeability tensor exhibit nonzero off-diagonal components giving evidence of the nonreciprocity of wave propagation in these nanostructures. These experimental results were analyzed within a recently developed multiscale modeling 4 and can be understood as arising from magnetostatic intergranular interactions via a mean-field approximation.…”

“…Our previous studies 4, [23][24][25][26][27][28] were focused on the determination of the effective material parameters ͑complex permittivity and permeability and effective Gilbert damping parameter͒ in the EMA and the evaluation of the magnetization of these NCs. In the current investigation, we evaluate the microwave properties of selected NCs by combining the microstrip line method and the SWS method.…”

Towards electromagnetic metamaterial: Negative permeability spectra of YIG composite materials

“…To obtain the MNG material, negative permeability spectra of ferrites or ferromagnetic granular composite materials have been investigated [8][9][10][11][12][13]. We have studied the negative permeability spectra of sintered YIG under external magnetic field; the contributions of domain wall and gyromagnetic spin resonance to the frequency dispersions of permeability were evaluated by the numerical calculation using frequency dispersion formulae [10].…”