Domain Wall Resonance Research Articles

Temperature and frequency characteristics of low-loss MnZn ferrite in a wide temperature range

A low-loss Mn0.7Zn0.24Fe2.06O4 ferrite has been prepared by a solid-state reaction method. The MnZn ferrite has a high initial permeability, μi (3097), a high saturation induction, Bs (526 mT), a high Curie temperature, Tc (220 °C), and a low core loss, PL (≤ 415 kW/m3) in a wide temperature (25–120 °C) and frequency (10–100 kHz) range. As the temperature increases, an initial decrease followed by a subsequent increase of hysteresis loss, Ph, and eddy current loss, Pe is observed. Both Ph and Pe increase with increasing frequency. When f ≥ 300 kHz, a residual loss, Pr, appears. Pe increases with increasing temperature and frequency. The temperature and frequency dependence of Ph can be explained by irreversible domain wall movements, Pe by the skin effect, and Pr by domain wall resonance, respectively.

Effect of nonadiabatic spin transfer torque on domain wall resonance frequency and mass

The dynamics of a magnetic domain wall in a semi circular nanowire loop is studied by an analytical model and micromagnetic simulations. We find a damped sinusoidal oscillation of the domain wall for small displacement angles around its equilibrium position under an external magnetic field in the absence of currents. By studying the effect of current induced nonadiabatic spin transfer torque on the magnetic domain wall resonance frequency and mass, a redshift is found in the resonance frequency and domain wall mass increases by increasing the ratio of nonadiabatic spin torque to adiabatic contribution above 1.

Design and characteristics of flexible radio-wave absorber consisted of functional NiCuZn ferrite–polymer composites

This investigation aims to present a structural design of a radio-wave absorber incorporating NiCuZn ferrite granules in a contiguous polyepoxide matrix. Electromagnetic properties of the composites in radio-wave frequency were characterized by a combined transmission/reflection method in a coaxial airline fixture. The response of the composites to radio-wave field was attributed to macroscopic magnetic loss and dielectric loss relating to domain wall resonance, spin relaxation, and dipole polarization. Return losses were evaluated using equations representing a structure with a single-layer absorber terminated by a layer of perfect conductor. The maximum return loss was −48 dB occurring at 4.6 GHz for 8 mm thick samples with a ferrite/polyepoxide (F/P) volume ratio = 0.55. The variations of return losses with absorber thickness and absorption bandwidth were also investigated. The macroscopic effective permeability of the composites was computed by a numerical finite elemental analysis (FEA) using a periodic elliptical structure. The FEA calculations are more accurate than values predicted by empirical mixture rules assuming uniform distribution, especially at higher ferrite fractions (F/P ≥ 0.73).

Complex Permeability of LiZn/MnZn/PVC Composite Materials

The effect of particle content, size, and the fraction ratio of the double LiZn/MnZn ferrite filler in hybrid LiZn/MnZn/PVC composites on the frequency dispersion of complex permeability has been studied in the 1 MHz–3 GHz frequency range. The obtained relaxation type of permeability dispersion is due to the domain wall resonance, the natural ferromagnetic resonance, and the relaxation of magnetization rotation. The permeability and resonance/relaxation frequency of composites seem to be strongly affected by the change of particle content and fraction ratio of the double ferrite filler rather than by particle size.

Tuning of current-induced domain wall resonance frequency using Gd doping

The current-induced resonance frequencies of domain walls in parabolic pinning potentials are measured in Gd doped NiFe as a function of doping level. The modification of magnetic properties due to Gd doping results in an order of magnitude increase in resonance frequencies for 10% Gd doping, due to the induced out-of-plane anisotropy, and the resonance frequencies are excited at lower current densities compared to undoped NiFe. These results are reproduced using a one-dimensional model of domain wall resonance, and found to be in good agreement in the small oscillation amplitude limit.

Dielectric and magnetic properties of 0.4PZT+0.6NiCuZn-ferrite composites modified with P2O5–Co2O3

P 2 O 5 and Co2O3 have been introduced to 0.4PZT+0.6NiCuZn-ferrite composites in order to improve their electromagnetic properties, particularly for the suppression of electromagnetic interference. The nonlinear fitting of the results of permeability dispersion has revealed the relationships between domain wall resonance, spin rotation relaxation mechanisms, microstructure, and local induced anisotropy. The P2O5 additive can enhance the bulk density and static permeability due to its instantaneous liquid phase at low temperature. The existence of local induced anisotropy caused by ordering of Co ions results in a decrease in static permeability and an increase in the Q-factor. Meanwhile, the addition of Co2O3 can improve the dielectric constant and the loss tangent (tan δe) by increasing the oxygen vacancy concentration. The further decrease in tan δe of the samples codoped with P2O5 and Co2O3 is mainly attributed to P5+ in the grain boundary which can increase cation vacancies in the grain boundary region.

Complex permeability spectra of permendur composite materials

Complex permeability μ* and permittivity ϵ* spectra of permendur (Co50Fe50) composite materials have been studied in the microwave frequency range considering the application to the left-handed meta-materials and EMC devices. High surface electrical resistance of the permendur particles was achieved by the heat-treatment in order to suppress the eddy current effect in the high particle content composites. For the 82.6 vol.% composite, the μ' is 11 and less than 1 at 100 MHz and 6 GHz, respectively; the μ′′ shows the two peaks around 700 MHz and 3GHz due to the domain wall and gyromagnetic spin resonance. On the other hand, the ϵ′ is almost constant value of 28 and the ϵ′′ is almost zero in the frequency range from 100 MHz to 6 GHz. The calculated reflection loss of a single-layer electromagnetic wave absorber (EM absorber) designed by using permendur composites indicates less than −20 dB around the matching frequency of 1 GHz.

Dielectric and Magnetic Properties of Co$_{2}$O$_{3}$ Modified 0.4PZT${+}$0.6NiCuZn-Ferrite Composites

In order to improve the electromagnetic properties of 0.4PZT+0.6NiCuZn-ferrite composites for suppressing electromagnetic interference (EMI), Co2O3 was introduced. The effects of Co2O3 content on the electromagnetic properties of the composite materials were investigated. It was confirmed the existence of local induced anisotropy caused by ordering of Co2+ ions. Permeability spectra of the composites with different Co2O3 content had been resolved into contributions of domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion revealed the relationships among domain wall resonance, spin rotation relaxation mechanisms, and local induced anisotropy. This increase in local inducted anisotropy results in a decrease of initial permeability and an increase of Q-factor. Meanwhile, Co2O3 additive can improve the dielectric constant and the loss tangent (tandeltae) by increasing the oxygen vacancy concentration.

Magnetization dynamics in interlayer exchange-coupled in-plane/out-of-plane anisotropy bilayers

The static and high-frequency properties of bilayer systems consisting in a single-crystal garnet film with a perpendicular anisotropy exchange coupled with a thin Permalloy film with a small in-plane anisotropy have been investigated both numerically and experimentally. The dynamic susceptibility spectra computed by means of two-dimensional micromagnetic simulations extended to stratified films reveal clearly the existence of multiple resonance lines resulting from the coupling between different magnetic area (domain walls, domains) inside the garnet film and the Permalloy film. In particular, exaltation of intensive domain wall resonances occurs within the frequency range including the uniform gyromagnetic mode of the Permalloy film. The effect of the garnet and Permalloy film thicknesses on the features of the dynamic susceptibility spectra is then studied. The experimental power absorption spectra recorded on a Permalloy/YIGBiLuAl-like bilayer exhibit well-defined resonance lines, most of them assigned to coupled modes of the bilayer nicely predicted by the micromagnetic simulations. The strong direct exchange coupling at the interface between the two layers appears as a predominant factor for this metal-oxide system.

Complex permeability and permittivity spectra of polycrystalline Ni–Zn ferrite samples with different microstructures

Polycrystalline Ni–Zn ferrite samples with different microstructures have been prepared by the conventional ceramic technique, and their complex permeability and permittivity spectra have been studied. The permeability spectra have been resolved into contributions of domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion have revealed the relationships between domain wall resonance, spin rotation relaxation mechanisms, and microstructures. With increasing average grain size, the permittivity also gradually increased. However, extremely big grain size led to an uneven permittivity–frequency curve. These results may be rationalized in terms of the modifications of the microstructures brought about by the different sintering temperatures.

Electromagnetic properties of ferroelectric/ferromagnetic composite materials base on low temperature cofired ceramic technology

The Ni–Cu–Zn ferrite(NCZF)/BaTiO3(BT) composite materials with mass ratio of BT/NCZF (x)=10%, 20%, 30%, and 40% were synthesized by usual ceramic technology and sintered at 900°C to adapt to the low temperature cofired ceramic technology. The sintered density of the composite with x=40% is 5.454g∕cm3 which is higher than that of the Ni–Cu–Zn ferrite (5.349g∕cm3). The composites with x=10% and 20% have stable values of ε′ and lower values of tanδ. The ε′ of the composite with x=40% decreased from 256 to 39 when the frequency increased from 1MHzto1GHz. The microstructures of the sintered ceramics were observed and analyzed by scanning electron microscopy. The permeability spectra of the composites with different BT contents had been resolved into contributions of domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion revealed the relationships among the above two mechanisms and microstructures. The influences of different composition on the electromagnetic properties of the composites were investigated.

Microwave absorbing properties of Fe powders milled in various media

Principal factors determining the microwave-absorption material parameters (shape, size, and chemical and phase compositions of the particles) and their dispersion relations in a range from 0.1 to 3 GHz were determined for composites containing milled Fe particles as the filling agent. The basic physical mechanisms of the effect of the aforementioned factors were assumed to be the domain-wall resonance and ferromagnetic resonance.

High frequency magnetic mechanism of Ni-substituted Co 2Z hexagonal ferrite

The magnetic properties, especially the high frequency magnetic mechanism, of Ni-substituted Co 2Z hexagonal ferrite were studied. The polycrystalline Z-type hexagonal ferrite of Ba 3Ni x Co 2− x Fe 24O 41 (0 ≤ x ≤ 2) were prepared by solid-state reaction. The results indicate that Ni-substituted Co 2Z samples all exhibit typical soft magnetic character. Substitution of Ni for Co will turn the planar magnetocrystalline anisotropy of Co 2Z to uniaxial anisotropy when x ≥ 1, so that the permeability drops dramatically and domain wall resonance appears in the frequency spectra. With the rise of Ni amount or sintering temperature, domain wall resonance strengthens gradually.

Influence of microstructure on permeability dispersion and power loss of NiZn ferrite

Permeability spectra of NiZn ferrite with different microstructures had been resolved into contributions of domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion revealed the relationships among domain wall resonance, spin rotation relaxation mechanisms, and microstructures. Pcv (power loss) was analyzed by dividing Pcv into Ph (hysteresis loss) and Pe+Pr (eddy current loss and residual loss) from the frequency dependence of the power loss. When excited under large flux density, sample with larger average grain size and closed pores could obtain lower Pcv. This could be attributed to the fact that closed pores were not easy to block domain wall movement and grain boundaries became the predominant domain wall pinning factor. However, for the low induction condition, sample with small grain size had better performance on Pcv due to the fact that influence of the closed pores was more significant. With increasing frequency, Pe+Pr gradually became the predominant factors in Pcv, so the sample with small grain size was more suitable for high-frequency use.

Characteristics of domain wall motion in CoFe films for GHz frequency application

AbstractDynamic magnetization process is studied in CoFe films for high frequency application by using a time‐resolved imaging technique. The domain wall resonance has been found at 130 kHz in a slit‐patterned Co35Fe65 film with high saturation magnetization. The domain wall mobility of 20 m/sOe was observed at the resonant frequency. The effective wall mass, the viscous damping constant, and the restoring force constant were evaluated in the Co35Fe65 film. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analyses on the dispersion spectra of permeability and permittivity for NiZn spinel ferrites doped with SiO2

The permeability spectra of NiZn spinel ferrites with different amounts of SiO2 (0,0.3,0.5wt%) aggregated at the grain boundaries have been resolved into two contribution components: domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion show that the spin rotation relaxation mechanism makes major contributions to the dispersion. With increasing the contents of SiO2, the fitting results of permittivity dispersion spectra show a wider distribution of relaxation time and a longer relaxation time.

Microwave-absorbing properties of NiCoZn spinel ferrites

In this paper, the microwave-absorbing properties of (Ni 1− x − y Co x Zn y )Fe 2O 4 spinel ferrites have been investigated within the frequency range of 0.5–14 GHz. There are two kinds of resonance peaks observed in the permeability spectra: domain-wall resonances at lower frequency and spin-rotation resonances at higher frequency. The reflection loss (RL) calculations show that the prepared NiCoZn spinel ferrites are good electromagnetic (EM) wave absorbers in microwave range. In terms of the absorbing frequency band (AFB) and the matching thickness ( t m), (Ni 0.407Co 0.207Zn 0.386)Fe 2O 4 shows the best performances: t m=3.15 mm and the AFB is 8.64–11.2 GHz. Decreasing the weight ratio of NiCoZn ferrites in ferrites/wax composites, the matching thickness decreases and the AFB shifts to higher frequencies. Compared with the absorbers with single-layer ferrites, the absorbers with double-layers ferrites have better absorbing performances, such as a thinner matching thickness and a wider EM wave AFB.

Three-dimensional micromagnetic simulations of magnetic excitations in cylindrical nanodots with perpendicular anisotropy

The zero-field dynamic susceptibility spectra of ferromagnetic cylindrical nanodots with a large perpendicular anisotropy are investigated using full three-dimensional dynamic micromagnetic simulations. For the studied size regime where the dot diameter is near to the zero-field stripe domain period of the unpatterned film and equals twice the dot thickness, two nonuniform micromagnetic configurations can be stabilized, namely, a two-stripe domain state and a bubble state. For both cases, the computed dynamic susceptibility spectra exhibit multiple domain-wall resonances situated mainly below $20\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ and a set of domain resonances located essentially within the frequency range $20--80\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. For the two-stripe domain state, the lateral spatial confinement induces a splitting of the domain-wall modes existing in the continuous films. These domain-wall modes are distinguished by the dynamic magnetization profile along the domain-wall length. The evolution of the domain wall and domain resonance frequencies with the strength of the perpendicular anisotropy is reported. For the bubble state, flexural-type domain-wall modes, mixed domain-wall and domain modes, and domain modes localized in either the inner or the outer domain are observed. These magnetic excitations could be detected by either Brillouin light scattering or ferromagnetic resonance.

Nonlinear Oscillation Analysis and Stabilization Control of Magnetic Domain Wall

A chaotic region and stabilization method of domain-wall motion were examined by computer simulation. As a result, the chaotic domain-wall motion was distributed outside of (high frequency)-(large amplitude), and (low frequency)-(small amplitude) excitation region, and the bottom of region supported domain-wall resonance. In addition, the extended delayed feedback control (EDFC) method and Half-period-EDFC method that improved delayed feedback method were shown to be effective as a control method.

Microwave spectroscopy on magnetization reversal dynamics of nanomagnets with electronic detection

We demonstrate a detection method for microwave spectroscopy on magnetization reversal dynamics of nanomagnets. Measurement of the nanomagnet anisotropic magnetoresistance was used for probing how magnetization reversal is resonantly enhanced by microwave magnetic fields. We used Co strips of 2μm×130nm×40nm, and microwave fields were applied via an on-chip coplanar waveguide. The method was applied for demonstrating single domain-wall resonance, and studying the role of resonant domain-wall dynamics in magnetization reversal.