Gyromagnetic Properties Research Articles

Li2O-B2O3-SiO2-CaO-Al2O3 and Bi2O3 co-doped gyromagnetic Li0.43Zn0.27Ti0.13Fe2.17O4 ferrite ceramics for LTCC Technology

A modified low-temperature liquid phase sintering technique was attempted to fabricate Li0.43Zn0.27Ti0.13Fe2.17O4 ferrite ceramics with a compact structure and improved properties through the solid-state reaction route. Fixed amount of Li2O-B2O3-SiO2-CaO-Al2O3 (LBSCA) glass was added to Li0.43Zn0.27Ti0.13Fe2.17O4 powders to decrease the sintering temperature below 950°C, while the addition of Bi2O3 oxide contributed to optimizing the microstructure and improving the magnetic and gyromagnetic properties. Selected parameters including saturation magnetization (Ms), coercivity (Hc) and ferromagnetic resonance line width (ΔH) were investigated as a function of doping content, and their relationships with porosity and microstructure were also discussed. The sample resintered at 940°C with co-doping of 0.3wt% of LBSCA glass and 0.03wt% of Bi2O3 presented excellent magnetic and gyromagnetic properties of Ms =73.32emu/g, Hc =120 A/m and ΔH=163Oe, suggesting that it is promising in the LTCC phase shifter fabrications.

Composition, microstructures and ferrimagnetic properties of Bi-modified LiZnTiMn ferrites for LTCC application

The effects of Bi modification on the microstructural development and gyromagnetic properties of low-temperature sintered ferrites with composition of Li0.42Zn0.27Ti0.11Mn0.1Fe2.1−xBixO4 (x = 0.0-0.1) have been studied in order to adapt the development of low-temperature cofired ceramics technology (LTCC) and produce gyromagnetic devices with a multilayer process. In the present work, a pure spinel phase can be formed with a sintering temperature ranging from 880°C to 900°C, which allows them to be co-fired with silver. We found that Bi3+ ions could enter into the ferrite lattice, which enhanced the grain growth and densification during sintering due to the activation of the lattice. Results show that the modifying of x = 0.003 cannot only double saturation induction but also drastically reduce ferromagnetic resonance line width at 9.3 GHz, indicating that Bi modification is a good approach for lowing the sintering temperature of LiZnTiMn ferrites.

Effect of NiZn Ferrite Nanoparticles upon the Structure and Magnetic and Gyromagnetic Properties of Low-Temperature Processed LiZnTi Ferrites

NiZn ferrite nanoparticles (2–20 wt %) of composition Ni0.4Zn0.6Fe2O4 were introduced into LiZnTi ferrite of composition Li0.42Zn0.27Ti0.11Fe2.2O4 and sintered at a temperature of 920 °C for 2 h, well below that of the Ag melting point. Here, LiZnTi ferrites were prepared by a solid-state reaction method, and NiZn ferrite nanoparticles were fabricated by a hydrothermal chemical technique at 180 °C. A low ferromagnetic resonance (FMR) line width, low coercivity, and high magnetic moment were achieved after refinement of the heat treatment conditions of the mixture. Riveted full profile refinement of the X-ray powder diffraction patterns and analysis of Mossbauer spectra were employed to study the structure and caption distribution. The results confirm a pure spinel phase after processing. A narrow FMR line width of 152.5 Oe, a reduced coercivity of 132.9 A/m, and an improved saturation magnetization of 74.23 emu/g were obtained by way of the addition of 8 wt % NiZn ferrite nanoparticles.

Computation of Complex Eigenmodes for Resonators Filled With Gyrotropic Materials

In this thesis, the numerical computation of complex eigenmodes of cavity resonators filled with magnetically biased gyrotropic material is demonstrated. For this purpose, a dedicated solver based on the Finite Integration Technique (FIT) has been developed, efficiently implemented as well as successfully verified. Gyrotropic field problems arise, for instance, for the calculation of the resonance frequencies of ferrite-loaded resonators like the GSI SIS 18 cavity. Ferrites exhibit gyromagnetic properties with an anisotropic permeability, which furthermore depends both on frequency and bias field. Similarly, gyroelectric material such as magnetized plasmas can be described by a frequency- and bias field dependent permittivity tensor. Since these material tensors affect the system matrix of the eigenvalue problem, a dedicated solver is required. In this thesis, the FIT with a hexaedral staircase filling is employed for discretization. In the standard formulation, it is, however, limited to diagonally anisotropic materials. Hence, as one of the goals of this thesis, the FIT has been extended to gyromagnetic as well as gyroelectric materials in frequency domain. The derived expressions for the non-diagonal material matrices are fully consistent with the standard FIT when applied to non-gyrotropic materials. Moreover, their structure is manifestly Hermitian in the lossless case, even for non-equidistant grids. Due to the above-mentioned material requirements, the newly developed solver consists of two components: The first one is a magnetostatic solver based on the H_i-algorithm supporting nonlinear material to calculate the magnetic field excited by the bias current. Having obtained the field distribution, the material properties are evaluated locally in each mesh cell at the specified working point. The second component is a Jacobi-Davidson type eigenvalue solver for the iterative solution of the nonlinear eigenproblem. To be capable of handling material losses, the eigensolver also supports non-Hermitian eigenproblems. What is more, efficient parallel computing on machines with distributed memory is possible. To this end, an ordering of the FIT-DOFs different from the standard scheme is implemented, which results in an increased computation to communication ratio. Furthermore, all DOFs that vanish a priori due to several reasons are completely removed from the vectors and matrices. All in all, gyrotropic eigenproblems discretized with several millions of mesh cells can be solved in a reasonable time by the developed solver. The validity of the numerically obtained results is confirmed by thorough comparisons with (semi-)analytical calculations. As an application example, an eigenmode analysis of the GSI SIS 18 cavity is carried out. Since the required material data are not available in the data sheet of the manufacturer, designated measurements of the magnetic characteristics of the Ferroxcube 8C12m ferrite ring cores, which are installed inside the GSI SIS 18 cavities, were performed. Among these characteristics are the complex permeability as a function of frequency and bias magnetic field strength at low radio-frequency power levels as well as the B-H curve. The measurement methods together with the detailed data analysis including the presentation of evaluated data are supplemented to this thesis. The scalar, isotropic permeability retrieved this way is used for the cavity simulations. The obtained values for the resonance frequency and quality factor for the fundamental mode are in accordance with available measurement data. To demonstrate the further potential of the solver, also higher-order modes are investigated and an outlook on possibly advantageous 2-directional bias schemes is given.

Grain growth, densification, and gyromagnetic properties of LiZnTi ferrites with H3BO3-Bi2O3-SiO2-ZnO glass addition

LiZnTi (Li0.43Zn0.27Ti0.13Fe2.17O4) ferrites doped with 0.35 wt. %–1.5 wt. % H3BO3-Bi2O3-SiO2-ZnO (BBSZ) were synthesized through a low temperature ceramic sintering process. The grain growth of LiZnTi ferrites was discussed by using the liquid phase sintering mechanism. BBSZ promoted grain growth via liquid phase sintering, and the optimum addition of BBSZ could reduce porosity of the sample. Meanwhile, selected parameters including saturation induction (BS), coercivity (HC) and ferromagnetic resonance line width (ΔH) were measured as functions of doping content, and their relationships with ferrite porosity and microstructure were also discussed. The LiZnTi ferrite samples containing x = 0.5, 0.65, and 0.8 sintered at 920 °C, 900 °C, and 880 °C, respectively, exhibited high BS and low ΔH values at 9.3 GHz. The addition of proper content of BBSZ can not only improve BS but also reduce HC and ferromagnetic resonance line width (ΔH) by low temperature (∼900 °C) liquid phase sintering.

A note on the gyromagnetic properties of the hydrogens

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Metabolic imaging of the human heart: clinical application of magnetic resonance spectroscopy

Cardiovascular MRI has earned its place in the field of clinical cardiac imaging. Regularly used techniques include anatomical imaging, functional imaging, perfusion, and delayed enhancement (DE). Cardiac magnetic resonance spectroscopy...

Magnetless Nonreciprocal Metamaterial (MNM) Technology: Application to Microwave Components

A magnetless nonreciprocal metamaterial (MNM), consisting of traveling-wave resonant ring particles loaded by transistor <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm s}$</tex></formula> and exhibiting the gyromagnetic properties as ferrites, without their size, weight, cost, and monolithic microwave integrated circuit incompatibility drawbacks, was recently introduced in 2011 by Kodera <etal xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> This paper presents the first extensive investigation of the applicability of MNM technology to nonreciprocal microwave components. It recalls the key principle of the MNM, provides basic MNM design guidelines, explains coupling mechanism between a microstrip line and MNM rings, and demonstrates two nonreciprocal MNM components based on a microstrip-ring configuration, an isolator, and a circulator. Although these components have not been fully optimized, they already exhibit attractive performance and provide a proof-of-concept that MNM technology has a potential for microwave nonreciprocal microwave components with substantial benefits compared to their ferrite and active-circuit counterparts.

Magnetically tunable silicon-ferrite photonic crystals for terahertz circulator

The gyromagnetic properties of ferrite materials and the nonreciprocal property of a silicon-ferrite photonic crystal cavity are investigated in the terahertz region. Through the structure optimization and analysis of defect mode coupling, we design a magnetically tunable circulator, of which central operating frequency can be tuned from 180 to 205GHz and the maximum isolation is 65.2dB. Moreover, the further study shows that the gyrotropy, dispersion, and ferromagnetic loss of ferrite materials under the different external magnetic fields greatly affect the transmission and isolation property of this device. This circulator is flexible to realize functions of controllable splitting, routing, filtering and isolation by changing the external magnetic field for the THz applications.

Microstructural and magnetic properties of thick (≥10 μm) magnetron sputtered barium ferrite films

This work focuses on the properties of 10–15 μm thick barium M-type hexaferrite (BaFe 12O 19 or BaM) films deposited by non-reactive RF magnetron sputtering on alumina substrates. High deposition rates were achieved through deposition at room temperature and operation at an RF power of 100 W. By varying sputtering gas pressure, the dc magnetic properties were correlated with structural, morphological and compositional properties obtained by X-ray diffraction (XRD), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS), respectively. A deposition pressure of P=3 Pa enables one to reach the best compromise between high deposition rate (0.75 μm/h) and adequate crystallographic, stoichiometric and magnetostatic properties. Finally the gyromagnetic properties at high frequency were assessed through the characterization of coplanar isolator up to 60 GHz. As such, hexaferrite films prepared using this technique may offer opportunities for the next generation of self-biased planar microwave devices.

Multilayer structures with optical characteristics controlled by a magnetic field

The consideration of the gyromagnetic properties of multilayer structures with one or more magnetically active components shows that the application of a magnetic field to such structures imparts magnetically controlled optical properties to them. The effect of a magnetic field on the reflection coefficient of the multilayer structures manifests itself in two phenomena: a shift of the maximum of the spectral curve of the resonant reflection coefficient and a change (increase or decrease) in the bandwidth of this curve. The more pronounced of these two effects is the change in the bandwidth of the spectral curve of the reflection coefficient. The orientation (transverse or longitudinal) of the magnetic field applied to the multilayer structure determines important specific features of these effects. Calculation performed for two types of multilayer structures (Y3Fe5O12−Gd3Ga5O12 and Y3Fe5O12−SiO2) shows the possibility of their practical use, for example, in fiber optics.

Multilayer structures with magnetically controlled light transmission

Taking into account the gyromagnetic properties of multilayer two-component structures of which one or both components are magnetoactive materials shows that their optical properties can be controlled by an external magnetic field. In particular, when applied to multilayer structures with a phase shift (defect), the magnetic field changes (decreases or increases) the width of the spectral resonance curve of the transmission coefficient. The application of longitudinal and transverse (relative to the light propagation direction) magnetic fields gives different results. Analysis shows that the effects observed may find application, for example, in fiber optics.

A reversed gyromagnetic effect in chromium dioxide particles

The gyromagnetic properties of CrO 2 recording particles have been investigated and compared to those of γ-Fe 2O 3, which have previously been subject to similar studies. Rotational remanent magnetization (RRM) was determined as a function of rotation speed and of the strength of the magnetizing alternating field (AF). Gyromagnetic remanent magnetization (GRM) acquired by anisotropic samples in a static experiment was measured for various peak AF as a function of the angle between the AF and the axis of anisotropy. The asymmetry of GRM curves obtained with non-saturating fields may be related to the incoherent reversal mode of the particles. While GRM (RRM) of the γ-Fe 2O 3 particles had the sign expected theoretically, the gyromagnetic remanences obtained for CrO 2 in both types of experiments were of opposite signs. Possible reasons for the reversed gyromagnetic effect are discussed.

Millimeter-wave semiconductor two-port network at 77K

The gyromagnetic properties of magnetized ferrites are widely used in many novel rf and microwave devices. According to the Drude model, similar principles should also be applicable to magnetized semiconductors due to its gyroelectric properties. In this study, an axially magnetized semiconductor resonator is characterized in terms of bias field and signal frequency. The resonance and loss regions are identified at 77K. The affect of changing material and geometrical properties of the resonator on the splitting and tuning behavior of normal modes are illustrated. Green's Function approach is used to derive the S-parameters of a two port semiconductor network. The network response and the material properties can be used to calibrate the semiconductor material before measuring the millimeter-wave properties of the resonator. This theoretical analysis may prove to be vital in realizing miniaturized and broadband semiconductor junction circulators and filters for high-Tc superconductive circuits.

Reflection and transmission for gyroelectromagnetic biaxial layered media

A planar structure consisting of layers of different media is considered. The material of each layer is linear and homogeneous but anisotropic and, in general, exhibits biaxial, gyroelectric, and gyromagnetic properties. Thus most materials used in practice fall into the general category considered here. The structure has free space on one side and an isotropic medium (e.g., a dielectric or a metal) on the other side. A plane electromagnetic wave with arbitrary direction and polarization is incident upon the structure. The propagation constants and the components of the electric and magnetic fields are determined in each layer. A chain-matrix approach is implemented to obtain reflection and transmission coefficients for the structure.

The spin of the electron according to stochastic electrodynamics

By making use of the method of moments we study some aspects of the statistical behavior of the nonrelativistic harmonic oscillator according to stochastic electrodynamics. We show that the random rotations induced on the particle by the zero-point field account for the magnitude of the spin of the electron, the result differing from the correct one(3/4)h 2 by a factor of2. Assuming that the measurement of a spin projection may be effectively taken into account by considering the action of only the subensemble of the field with the corresponding circular polarization, the calculated value of the spin projection comes out to be the correct one within a factor of order unity. The radiative corrections give rise to both the Lamb shift and the anomalous magnetic moment of the electron, the latter being evaluated to within a factor of2. The magnetic and gyromagnetic properties of the electron come out to be in agreement with quantum mechanics. Interference effects are shown to occur when evaluating the average value of the square of the angular momentum.

Dynamic magnetic susceptibility of polycrystalline ferrites

The magnetic susceptibility of magnetized ferrites is described by the tensor of second rank\(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftrightarrow}$}} {\chi } \) at microwave frequencies. The tensor nature of the susceptibility is determined by the gyromagnetic properties of the electron spins and is associated with the phenomenon of ferromagnetic resonance (FMR). A considerably greater absorption line width than in corresponding single crystals is characteristic for FMR in polycrystals. As a rule, the resonance curve of a polycrystal turns out to be of more complex shape, it is usually nonsymmetric and can even have several absorption maximums. These singularities are related to the structure of the polycrystalline materials, consisting of sets of crystal grains, and can be understood in general features from the viewpoint of the modern theory of FMR. The magnetic anisotropy, inherent to crystals, and the random orientation of the crystallographic axes of the grains relative to the static magnetizing field H0 result in different FMR conditions in the individual crystallites. The main difficulty in a theoretical investigation of resonance absorption of microwave electromagnetic energy in polycrystals is in taking account of the interaction between the magnetic moments of the individual grains. This difficulty has still not been overcome up to now, and hence it is customary to analyze FMR in two limiting cases. In the “independent grains” approximation, when the relationship between the magnetic moments of the crystallites turns out to be so weak that it can be neglected, the field dependence of the absorbed microwave power is successfully computed [1,2,3]. A spin-wave analysis [4,5] permits computation of the Linewidth and resonance field in the other extreme case, in the strong binding approximation when the effect of can be considered a small perturbation.

Relaxation of rare earth and cobalt ions in polycrystalline yttrium iron garnet

Relaxation at room temperature of rare earths and cobalt ions in ferrimagnetic garnets has been studied by measuring the three linewidths : ΔH, resonance linewidth, Δ H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</inf> , effective linewidth, ΔH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</inf> , spinwave linewidth. These linewidths have been measured at 9 GHz Δ H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</inf> , far from resonance, Δ H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> in perpendicular and in parallel pumps. From experimental results, relations between ΔH, Δ H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</inf> and Δ H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> have been found which are in good agreement with the theory. The broadening δ (ΔH), due to the introduction of rare earths ions, allows the relaxation time τ (about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> sec) of some rare earths ions to be deduced from Kittel's theory. At room temperature, this theory explains the gyromagnetic properties of Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> , Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> , Dy <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> , Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. An adaptation of this theory allows us to explain also the behaviour of Gd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. Relation between δ (ΔH) and the saturation magnetization 4π M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> are explained for the Sm, Dy, Ho and Er ions by an extension of Kittel's theory, but this explanation is not unique.

Propagation of Guided Electromagnetic Waves in Semiconductors in a Longitudinal Magnetic Field

The propagation of electromagnetic waves in a circular waveguide, filled over a finite distance with a longitudinally magnetized semiconducting medium, is studied both theoretically and experimentally. The existing theory of the propagation of guided electromagnetic waves in gyromagnetic media is extended by consideration of the attenuation of the wave by the medium. It follows from the theory presented that analytical expressions for the dependence of the propagation on the magnetic field can only be derived if the gyromagnetic properties of the semiconductor are sufficiently weak. It is shown that values of the concentration N, the mobility μ and the scattering time τ (and hence the effective mass m*) of the charge carriers can be found by measuring the Faraday rotation, as well as by measuring the attenuation of a plane-polarized wave due to the charge carriers in the medium. Furthermore, these two measurements are shown to provide a convenient way of determining the dielectric constant of a semiconductor in the microwave region. In order to verify the theory experiments were carried out on n-type GaAs. Both the Faraday rotation and the attenuation of the wave were measured, taking into account the influence of interferometer effects due to the finite length of the semiconducting medium. The experimental results obtained for the Faraday rotation and the attenuation were consistent with each other and were in excellent agreement with the theory. The dielectric constant εl of GaAs was found to be 12.77±0.1.

Relaxational Behavior of Fine Magnetic Particles

Weil and others have used the temperature variation of remanence and a formula of Néel's to determine volume-distribution curves for a powder of single-domain particles. The basic principle is that the time constant for spontaneous reversal of the magnetization, through thermal agitation, is effectively infinite for particle volume v&amp;gt;vc and zero for v&amp;lt;vc, where vc varies with absolute temperature T. Néel's derivation is open to criticism, in that the gyromagnetic properties of the particles are taken into account only up to a certain point in the argument and are thereafter ignored. A new formula has been derived by adaptation of a method of Kramers to angular coordinates and to a gyroscopic equation of motion. Like Néel's theory, this gives for the mean rate of transition between orientations a formula of the form v = c exp(−W/kT); W is the same in both theories, but in the new theory c = (γ′/2)(vJsHc3/2πkT)12. Here Hc = critical field for static reversal, Js = spontaneous magnetization, γ′ = (2ηJs)[(ηJs)2+1/γ2]−1, γ = (magnetic moment)/(angular momentum), η = coefficient in the damping torque −ηM×(dM/dt) in Gilbert's equation of motion. The new values of v/T vs time constant do not differ seriously from Néel's.