Ferromagnetic resonance in magnetic composites (original) (raw)
Related papers
Magnetic Nanocomposites at Microwave Frequencies
Engineering Materials, 2010
Most conventional magnetic materials used in the electronic devices are ferrites, which are composed of micrometer-size grains. But ferrites have small saturation magnetization, therefore the performance at GHz frequencies is rather poor. That is why functionalized nanocomposites comprising magnetic nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm, and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have a significant potential for the electronics industry. When the size of the nanoparticles is smaller than the critical size for multidomain formation, these nanocomposites can be regarded as an ensemble of particles in single-domain states and the losses (due for example to eddy currents) are expected to be relatively small.
Ferromagnetic Resonance Studies in Magnetic Nanosystems
Magnetochemistry
Ferromagnetic resonance is a powerful method for the study of all classes of magnetic materials. The experimental technique has been used for many decades and is based on the excitation of a magnetic spin system via a microwave (or rf) field. While earlier methods were based on the use of a microwave spectrometer, more recent developments have seen the widespread use of the vector network analyzer (VNA), which provides a more versatile measurement system at almost comparable sensitivity. While the former is based on a fixed frequency of excitation, the VNA enables frequency-dependent measurements, allowing more in-depth analysis. We have applied this technique to the study of nanostructured thin films or nanodots and coupled magnetic layer systems comprised of exchange-coupled ferromagnetic layers with in-plane and perpendicular magnetic anisotropies. In the first system, we have investigated the magnetization dynamics in Co/Ag bilayers and nanodots. In the second system, we have st...
Ferromagnetic resonance in arrays of highly anisotropic nanoparticles
The European Physical Journal B, 2006
We present in this study computational simulations of the ferromagnetic resonance response of magnetic nanoparticles with a uniaxial anisotropy considerably larger than the microwave excitation frequency (in field units). The particles are assumed to be randomly oriented in a two dimensional lattice, and are coupled by dipolar interactions through an effective demagnetization field, which is proportional to the packing fraction. We have included in the model fluctuations in the anisotropy field (H K) and allowed variations in the demagnetizing field. We then analyzed the line shape and line intensity as a function of both fields. We have found that when HK is increased the line shape changes drastically, with a structure of two lines appearing at high fields. The line intensity has a maximum when H K equals the frequency gap and decreases considerably for larger values of the anisotropy. The effects of fluctuations in HK and variations in the packing fraction have been also studied. Comparison with experimental data shows that the overall observed behavior is dominated by the particles with lower anisotropy.
Measurements are presented of the frequency-dependent (10 MHz–18 GHz) complex magnetic susceptibility of colloidal suspensions of different concentrations of nano-particles of magnetite in a hydrocarbon. Studies of three colloids, fluids, 1, 2 and 3, with packing fractions of magnetite particles of 0.22, 0.1 and 0.05, were made at different magnetic polarising fields in the range 0–100 kA m À1. It is shown that the fluid with the highest packing fraction exhibits the highest resonant frequency. Using a local field approximation it has been shown that this observation can be explained by simply considering magnetic interactions between individual particles in the fluid. It is not necessary to invoke the presence of clustering as a function of increased packing fraction.
Electrical and magnetic properties of nanomaterials containing iron or cobalt nanoparticles
Inorganic Materials, 2007
We have prepared nanocomposites consisting of narrowly sized metal-containing nanoparticles embedded in a polyethylene matrix and have established conditions for the fabrication of thick films and bulk materials from the synthesized polymer powders. Dielectric permittivity and resistivity measurements demonstrate that the electrical properties of the nanocomposites depend significantly on the nanoparticle size and content.The microwave absorption and permittivity of the materials are shown to vary little in a broad frequency range. The magnetization (including the remanent one) of the cobalt-containing nanomaterials is higher than that of the iron-containing samples.
Magnetic properties of cobalt-ferrite nanoparticles embedded in polystyrene resin
Journal of Applied Physics, 2006
Samples of maghemite and cobalt-ferrite nanoparticles ͑sizes, 3-10 nm͒ were prepared by cross-linking sulfonated polystyrene resin with aqueous solutions of ͑1͒ FeCl 2 , ͑2͒ 80% FeCl 2 + 20% CoCl 2 , ͑3͒ FeCl 3 , and ͑4͒ 80% FeCl 3 + 20% CoCl 2 by volume. Chemical analysis, x-ray powder-diffraction, and 57 Fe Mössbauer spectroscopic measurements show that samples 1 and 3 consist of ␥-Fe 2 O 3 nanoparticles ͑sizes, ϳ10 and 3 nm͒ and sample 2 and 4 consist of Co x Fe 3−x O 4 nanoparticles ͑sizes, ϳ10 and 4 nm͒. The temperature dependence of the zero-field-cooled and field-cooled magnetizations at low temperatures, together with a magnetic hysteresis in the M versus H data below blocking temperatures, demonstrate superparamagnetic behavior. The introduction of Co in the iron oxide-resin matrix results in an increase in the blocking temperature of nanoparticles.
Broadband Permeability Spectra of Flake-Shaped Ferromagnetic Particle Composites
IEEE Transactions on Magnetics, 2017
Broadband permeability spectra of aligned ferromagnetic flakes embedded in a nonmagnetic polymer matrix have been measured using an APC-7 coaxial line within the frequency range 10 MHz-18 GHz. These spectra reveal two well-defined resonance lines. The low-frequency one (sub-GHz range) has previously been attributed to the fundamental vortex translation mode in a multidomain magnetic structure, whereas the high-frequency resonance (beyond 1 GHz) is assigned to the natural spin resonance. A two-level analytical model combining a spin dynamics description including these two contributions at the flake scale and a Maxwell-Garnett mixing rule at the composite scale has been developed and reproduces very satisfactorily the experimental spectra in terms of resonance frequencies, resonance linewidths, and resonance mode amplitudes.
High-frequency response of nanostructured magnetic materials
Journal of Magnetism and Magnetic Materials, 2009
This paper reports a brief overview on recent developments regarding the high-frequency response in the GHz range of nanostructured magnetic materials. Emphasis is placed on the linear regime in the frequency domain characterized by the dynamic susceptibility spectrum. Some modeling tools and experimental probes allowing determination of the dynamic susceptibility spectrum are first rapidly reviewed and their respective advantages and disadvantages are discussed. Next, some illustrative examples of the high-frequency response of nanopatterned materials based on recent works are presented. The role played by the shape of the element on the characteristics of excitation spectrum is underlined. Lastly, some prospects are proposed and promising trends are highlighted. & 2009 Published by Elsevier B.V. 2. Modeling tools 2.1. Context The magnetization dynamics is analyzed by adopting the micromagnetic formalism where the magnetic medium is
Ferromagnetic resonance in an ensemble of nanoparticles with randomly distributed anisotropy axes
Journal of Magnetism and Magnetic Materials, 2008
Spectra of absorbed power as probed by ferromagnetic resonance (FMR) are numerically calculated within a macro-spin model for single domain nanoparticles using Landau-Lifshitz-Gilbert dynamics. Randomly distributed anisotropy axis and a distribution of anisotropy energies result in a significant broadening of the FMR signal as compared to an ensemble of particles all having the same anisotropy. Additionally, a temperature dependence of the shift of the resonance frequency is obtained which is in a qualitative agreement with experimental data on single domain nanoparticles. r