Magnetoelectric Microwave Research Articles

Determining the preferable polarization loss for magnetoelectric microwave absorbers by strategy of controllably regulating defects

Regulating the inner defects could lead to transformation of the prominent dielectric loss for the microwave absorbers, which is a necessary foundation to explore the preference type of dielectric loss mechanism. Herein, in this work, selective molar ratios of melamine/cetyl trimethyl ammonium bromide (CTAB) precursors were designed to construct the Fe/C/N based hybrid materials. The results demonstrate that the dominated polarization loss can be obtained with the high molar ratio of melamine/CTAB due to the improved level of defects density such as point defects, heterointerface distortion, etc. Differently, it is easy to obtain the conductive carbon phase and high crystallinity degree of Fe3C with a low melamine/CTAB molar ratio, achieving significantly conductive loss. Finally, the Fe/C/N hybrid with dominant polarization loss harvests a broad bandwidth of 6.2 GHz at 1.7 mm, verifying the superiority of polarization loss for enhancing electromagnetic absorption performance. Furthermore, simulation results prove that this composite possesses the desirable radar cross section (RCS) reduction and electromagnetic protection for the human head, indicating the potential applications in both military and civilian fields.

Compact Dual Microwave/Millimeter-Wave Planar Shared-Aperture Antenna for Vehicle-to-Vehicle/5G Communications

This paper presents a compact dual-port dual-frequency planar shared-aperture antenna with large frequency ratio. It consists of a microwave magneto-electric (ME) dipole antenna and a millimeter-wave parallel-plate resonator antenna (PPRA). It has two vertical conducting walls that form an upper-band parallel-plate resonator and meanwhile provide a magnetic source to the lower-band ME dipole. The design is a shared-aperture structure and is therefore very compact. For demonstration, a dual-frequency antenna simultaneously covering the 5.9-GHz vehicle-to-vehicle (V2V) band (5.855-5.925 GHz) and the 28-GHz 5G band (27.5-28.35 GHz) was designed, fabricated, and measured. Good agreement between the measured and simulated results was found. The lower and upper bands have the measured 10-dB impedance bandwidths of 41.6% (5.30-8.08 GHz) and 6.66% (27.15-29.02 GHz), and measured peak antenna gains of 5.80 dBi and 8.46 dBi, respectively. The antenna can be used on vehicular platforms for providing V2V communications and 5G millimeter-wave connections simultaneously.

Shear-strain-mediated large nonvolatile tuning of ferromagnetic resonance by an electric field in multiferroic heterostructures

Controlling magnetism by an electric field is of critical importance for the future development of ultralow-power electronic and spintronic devices. Progress has been made in electrically driven nonvolatile tuning of magnetic states in multiferroic heterostructures for the information storage industry, which is exclusively attributed to the ferroelectric-polarization-switching-induced interfacial charge effect or nonlinear lattice strain effect. Here, we demonstrate that a hitherto unappreciated shear strain in the ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate triggered by an electric field can be adopted to obtain robust nonvolatile control of the ferromagnetic resonance in an elastically coupled epitaxial Fe70Rh30 thin film. The disappearance of the resonance peak in a low-field-sweeping mode and the large resonance field shift of 111 Oe upon polarization switching demonstrate a strong shear-strain-mediated magnetoelectric coupling effect. In particular, in situ Kerr measurement identifies that the nonvolatile magnetic switching purely originates from electric-field-induced 109° ferroelastic domain switching rather than from 71°/180° ferroelectric domain switching even without the assistance of a magnetic field. This discovery illustrates the role of shear strain in achieving electrically tunable nonvolatile modulation of dynamic magnetic properties, and favors the design of future energy-efficient magnetoelectric microwave devices.

Modelling of microwave magnetoelectric effect in a laminate of ferrite and piezoelectric bimorphs

The article discusses the magnetoelectric (ME) effect in a layered structure of ferrite and two piezoelectric bimorphs. Proposed theoretical model predicts a giant microwave ME coupling at the coincidence of high-order harmonics of electromechanical resonance and ferromagnetic resonance for the ferrite. In such structures, ME interaction is known to be a result of mechanical strains. Using two piezoelectric bimorphs results in the excitation of high-order harmonic modes that are suppressed in ferrite-piezoelectric bilayers. ME coefficient of 300 V/(cm·Oe) at 5 GHz is predicted for the fifth resonance mode in the laminate of yttrium-iron garnet and two langatate bimorphs. The phenomenon can be used for the realization of ME interaction based microwave devices.

Studies on mechanical loss in converse magnetoelectric effect under multi-physical field

By means of the technic for measuring resonant converse magnetoelectric (CME) effect, the mechanical loss of PZT/Terfenol-D/PZT tri-layer symmetric magnetoelectric laminated composites under multi-physical field loads such as bias magnetic field, driven voltage and ambient temperature is systematically measured in this paper. The experimental results show that the mechanical loss in CME effect increases initially with the increase of the bias magnetic field, and approaches to a broad maximum value at 250–500 Oe. Further increasing bias magnetic field leads to the decrease of mechanical loss. The mechanical loss increases rapidly with the increase of driven voltage amplitude, especially in the medium magnitude of the bias magnetic field. While, there is little influence of voltage on the mechanical loss under the higher bias magnetic fields. Importantly, the mechanical loss increases monotonically as the increase of ambient temperature. The research results of the mechanical loss under multi-physics fields in this paper can provide a basic principle of CME improvement by reducing the mechanical loss. Therefore, this research is quite significant to the CME based applications, such as, magnetoelectric transducers, magnetoelectric microwave devices, multiferroic antennas and so on.

Modeling of magnetoelectric microwave devices

The possibility of computer modeling implementation of electrically controlled magnetoelectric (ME) microwave devices is considered. The computer modeling results of different structures of ME microwave devices based on layered ferrite-piezoelectric structure formed on the slot line, microstrip line and coplanar waveguide are offered. Results are reported as frequency dependencies of insertion losses of ME devices.

In-plane anisotropic effect of magnetoelectric coupled PMN-PT/FePt multiferroic heterostructure: Static and microwave properties

The effects of the electric and magnetic field variation on multiferroic heterostructure were studied in this work. Thin films of polycrystalline Fe50Pt50 (FePt) were grown by dc-sputtering on top of the commercial slabs of lead magnesium niobate-lead titanate (PMN-PT). The sample was a (011)-cut single crystal and had one side polished. In this condition, the PMN-PT/FePt operates in the L-T (longitudinal magnetized-transverse polarized) mode. A FePt thin film of 20 nm was used in this study to avoid the characteristic broad microwave absorption line associated with these films above thicknesses of 40 nm. For the in-plane easy magnetization axis (01-1), a microwave magnetoelectric (ME) coupling of 28 Oe cm kV −1 was estimated, whereas a value of 42 Oe cm kV −1 was obtained through the hard magnetization axis (100). Insight into the effects of the in-plane strain anisotropy on the ME coupling is obtained from the dc-magnetization loops. It was observed that the trend was opposite along the easy and hard magnetic directions. In particular, along the easy-magnetic axis (01-1), a square and narrow loop with a factor of Mr/MS of 0.96 was measured at 10 kV/cm. Along the hard-magnetic axis, a factor of 0.16 at 10 kV/cm was obtained. Using electric tuning via microwave absorption at X-band (9.78 GHz), we observe completely different trends along the easy and hard magnetic directions; Multiple absorption lines along the latter axis compared to a single and narrower absorption line along the former. In spite of its intrinsic complexity, we propose a model which gives good agreement both for static and microwave properties. These observations are of fundamental interest for future ME microwave components, such as filters, phase-shifters, and resonators.

Electric field modulation of ultra-high resonance frequency in obliquely deposited [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011)/FeCoZr heterostructure for reconfigurable magnetoelectric microwave devices

The multiferroic heterostructure of FeCoZr/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) (PMN-PT) prepared by oblique sputtering deposition technique shows a large electrical tunability of ultra-high ferromagnetic resonance frequency from 7.4 GHz to 12.3 GHz. Moreover, we experimentally demonstrate the possibility of realizing electrically reconfigurable magnetoelectric microwave devices with ultra-low power consumption by employing the heterostructure under different resetting electric fields through a reconfiguration process. In particular, the tunability of the FeCoZr/PMN-PT heterostructure from 8.2 GHz to 11.6 GHz can retain in a remanent state after releasing the resetting electric field. This suggests that the tunable microwave devices based on such heterostructures are permanently reconfigurable by simply using a trigger electric field double-pulse which requires much less energy than that of the conventional ones wherein an electric field needs to be constantly applied during operation.

A generalized lumped-element equivalent circuit for tunable magnetoelectric microwave devices with multi-magnetoelectric laminates

According to the microwave transmission principle and the mechanism of ferromagnetic resonance, a generalized lumped element model for electrically and magnetically magnetoelectric tunable microwave devices with multi-magnetoelectric laminates is established. This model is introduced the RLC series resonant circuit and an ideal transformer model to characterize the ferromagnetic resonance effect and the coupling between microstrip line and the magnetoelectric laminates. Then, the model is degenerated to an existing microwave resonator, which contains only a single block magnetoelectric laminate, and transmission characteristics results predicted by the lumped element model are compared with the experimental results and the electromagnetic simulated results. It is found that the lumped circuit model can effectively predict the center frequency and bandwidth of the resonator. After that, the lumped element model is used to predict the band characteristics and the magnetic and electric tunability of the filter with multi-magnetoelectric laminates. The results show that the application of multi-magnetoelectric laminates in filters can not only broaden bandwidth, but also control the work frequency band by tuning the external electrostatic and magnetostatic field on the magnetoelectric laminates. Therefore, considering the practicality and versatility of microwave devices with multi-magnetoelectric laminates, the effective lumped element model can provide the theoretical basis for the design of novel magnetoelectric devices.

Topological properties of microwave magnetoelectric fields.

Collective excitations of electron spins in a ferromagnetic sample dominated by the magnetic dipole-dipole interaction strongly influence the field structure of microwave radiation. A small quasi-two-dimensional ferrite disk with magnetic-dipolar-mode (MDM) oscillation spectra can behave as a source of specific fields in vacuum, termed magnetoelectric (ME) fields. A coupling between the time-varying electric and magnetic fields in the ME-field structures is different from such a coupling in regular electromagnetic fields. The ME fields are characterized by strong energy confinement at a subwavelength region of microwave radiation, topologically distinctive power-flow vortices, and helicity parameters [E. O. Kamenetskii, R. Joffe, and R. Shavit, Phys. Rev. E 87, 023201 (2013)]. We study topological properties of microwave ME fields by loading a MDM ferrite particle with different dielectric samples. We establish a close connection between the permittivity parameters of dielectric environment and the topology of ME fields. We show that the topology of ME fields is strongly correlated with the Fano-resonance spectra observed at terminals of a microwave structure. We reveal specific thresholds in the Fano-resonance spectra appearing at certain permittivity parameters of dielectric samples. We show that ME fields originated from MDM ferrite disks can be distinguished by topological portraits of the helicity parameters and can have a torsion degree of freedom. Importantly, the ME-field phenomena can be viewed as implementations of space-time coordinate transformations on waves.

Voltage‐Impulse‐Induced Non‐Volatile Ferroelastic Switching of Ferromagnetic Resonance for Reconfigurable Magnetoelectric Microwave Devices

A critical challenge in realizing magnetoelectrics based on reconfigurable microwave devices, which is the ability to switch between distinct ferromagnetic resonances (FMR) in a stable, reversible and energy efficient manner, has been addressed. In particular, a voltage-impulse-induced two-step ferroelastic switching pathway can be used to in situ manipulate the magnetic anisotropy and enable non-volatile FMR tuning in FeCoB/PMN-PT (011) multiferroic heterostructures.

Novel NiZnAl-ferrites and strong magnetoelectric coupling in NiZnAl-ferrite/PZT multiferroic heterostructures

Magnetic/piezoelectric multiferroic heterostructures with strong magnetoelectric (ME) coupling have recently attracted considerable interest. Since the ratio of magnetostriction λs over saturation magnetization Ms is a key factor to achieve strong magnetoelectric coupling in ferrite/piezoelectric multiferroic heterostructures, here we find a solution to tune λs/Ms by aluminum doping. We report aluminum-substituted NiZn-ferrites with different compositions (Ni0.65Zn0.35Fe2−xAlxO4, x = 0, 0.1, 0.3, 0.4, 0.6, 0.8 and 1) fabricated by a solid-state sintering process. The saturation magnetization of these NiZnAl-ferrites was reduced from 6000 to 900 G with increased Al doping, which was accompanied by a significantly narrowed ferromagnetic resonance linewidth from 1870 to 340 Oe. Meanwhile, saturation magnetostriction of these NiZnAl-ferrites was reduced from 6.67 to 1.40 ppm with increased amount of Al doping. Strong ME coupling was demonstrated in the NiZnAl-ferrites/PZT multiferroic heterostructures. A large piezoelectric deformation induced ferromagnetic resonance field change up to 42 Oe was observed in Ni0.65Zn0.35Fe1.2Al0.8O4/PZT heterostructures, corresponding to a large microwave ME coefficient of 4.2 Oe cm kV−1. These AlNiZn-ferrites and NiZnAl-ferrites/PZT heterostructures with large ME coupling provide a great opportunity for electrical tuning microwave devices.

Ferromagnetic resonance properties of Fe81−xNixGa19/Si(1 0 0) and Fe81−yNiyGa19/glass films

Two series of Fe81−xNixGa19/Si(100) and Fe81−yNiyGa19/glass films, where x or y=0–26, were made by the magnetron sputtering method. The film thickness (tf) was fixed at 100nm. We have performed three kinds of experiments on these films: (i) the saturation magnetostriction (λS) measurement; (ii) the easy-axis and hard-axis magnetic hysteresis loop measurements; and (iii) the ferromagnetic resonance (FMR) experiment to find the resonance field (HR) with an X-band cavity tuned at fR=9.6GHz. The natural resonance frequency, fFMR, of the Kittel mode at zero external field (H=0) is defined as fFMR≒ν[HK4πMS]1/2, where γ=2πν is the gyromagnetic ratio, HK and 4πMS are the uniaxial anisotropy field and saturation magnetization, and HK<<4πMS. The Gilbert damping constant, α, is calculated from the formula, α=[ν(ΔH)S]/(2fR), where (ΔH)exp=(ΔH)S+(ΔH)A, (ΔH)exp is the half-width of the absorption peak around the resonance field HR, (ΔH)S is the symmetric part of (ΔH)exp, and (ΔH)A is the asymmetric part. The degree of asymmetry, (ΔH)A/(ΔH)exp, is associated with the structural and/or magnetic inhomogeneities in the film. The main findings of this study are as follows: (A) fFMR tends to decrease, as x or y increases; (B) α decreases from 0.052 to 0.020 and then increases from 0.020 to 0.050, as x increases, and α decreases from 0.060 to 0.013 in general, as y increases; and (C) λS reaches a local maximum when x=22. We conclude that the Fe59Ni22Ga19/glass film should be the most suitable for application in magneto-electric microwave devices.

Microwave magnetoelectric fields and their role in the matter-field interaction

We show that in a source-free subwavelength region of microwave fields, there can exist field structures with a local coupling between the time-varying electric and magnetic fields differing from the electric-magnetic coupling in regular-propagating free-space electromagnetic waves. To distinguish such field structures from regular electromagnetic (EM) field structures, we term them as magnetoelectric (ME) fields. We study a structure and conservation laws of microwave ME near fields. We show that there exist sources of microwave ME near fields-the ME particles. These particles are represented by small quasi-two-dimensional ferrite disks with magnetic-dipolar-oscillation spectra. The near fields originating from such particles are characterized by topologically distinctive power-flow vortices, nonzero helicity, and a torsion degree of freedom. The paper consists of two main parts. In the first one, we give a theoretical background of properties of the electric and magnetic fields inside and outside of a ferrite particle with magnetic-dipolar-oscillation spectra resulting in the appearance of microwave ME near fields. In the second main part, we represent numerical and experimental studies of the microwave ME near fields and their interactions with matter. Based on the obtained properties of the ME near fields, we discuss possibilities for effective microwave sensing of natural and artificial chiral structures.

Theoretical Model of Electric Field Tunable FMR Frequency of Magnetoelectric Tri-Layered Structure

To study the magnetic-electrical-mechanical coupling mechanism of microwave ME (magnetoelectric) tri-layered structures, we proposed a theoretical model of electric tunable FMR (Ferromagnetic Resonance) frequency shift for bias magnetic field in different directions through the theory of Smith-Beljers and free energy density of ferrite. A deformation produced by the applied electric field called strain could be obtained through the theory of classical laminated plate. This model effectively predicts the stress of laminated structure increases when the piezoelectric coefficient increases, the shift of electric field tunable FMR frequency is more obvious when saturation magnetization and magnetostriction coefficient of ferrite increase. Moreover, it qualitatively explains the experimental phenomena that the directions of FMR frequency shift are opposite when apply the in-plane and out-of-plane magnetic field respectively, and provides a theoretical basis for electric field and magnetic field dual tunable microwave devices.

Ultra-low power electrically reconfigurable magnetoelectric microwave devices

We present an electrical tunable spiral inductor design and simulation results. By integrating (011) oriented single crystal ferroelectric substrate [Pb(Mg1/3Nb2/3)O3](1−x)-[PbTiO3]x (PMN-PT, x ≈ 0.32) with tunable and switchable remanent strain property, the tunability of such magnetoelectric microwave inductor can retain after releasing the electric actuation, i.e., electrically reconfigurable. A series of reconfigurable passive magnetoelectric microwave devices based on this concept are proposed and discussed. Those electrically reconfigurable magnetoelectric microwave devices have the advantage of low power consumption and fast and wide tunability, which can be potentially used for many applications.

The Electric Field Tuning Characteristics in the Strain-Mediated Ferrite-Piezoelectric Laminated Magnetoelectric Microwave Devices

This research focused on the numerical simulation of electric field tuning characteristics of the magnetoelectric microwave devices with the core of the laminated ferrite-piezoelectric magnetoelectric materials. Firstly, we proposed an expression for the shift of ferromagnetic resonance (FMR) frequency tuning by external electric field in piezoelectric layer, then substituted the expression of magnetoelectic (ME) constant into this expression, which can convert the electric field tuning on the laminated magnetoelectric materials into the equivalent magnetic field tuning on the ferrite layer. Secondly, we built a numerical analysis model for tunable magnetoelectric microwave device which is formed by the laminated magnetoelectric material and microstrip line, and put the equivalent magnetic field into this numerical model, then the numerical analysis model of novel tunable magentoelectric microwave device is completed. Taking a tunable ME microwave resonator for example, the S parameters calculated by the numerical model in this paper are in good agreement with experimental results both qualitatively and quantitatively. Considering the demand for the designing and applying of the microwave devices, we studied the effect of geometrical dimensions of the ferrite layer (YIG/GGG) on the return loss and the resonance frequency.

Soft magnetism, magnetostriction, and microwave properties of FeGaB thin films

A series of (Fe100−yGay)1−xBx (x=0–21 and y=9–17) films were deposited; their microstructure, soft magnetism, magnetostrictive behavior, and microwave properties were investigated. The addition of B changes the FeGaB films from polycrystalline to amorphous phase and leads to excellent magnetic softness with coercivity &amp;lt;1Oe, high 4πMs, self-biased ferromagnetic resonance (FMR) frequency of 1.85GHz, narrow FMR linewidth (X band) of 16–20Oe, and a high saturation magnetostriction constant of 70ppm. The combination of these properties makes the FeGaB films potential candidates for tunable magnetoelectric microwave devices and other rf/microwave magnetic device applications.

Magnetoelectric interactions in ferromagnetic-piezoelectric layered structures: Phenomena and devices

Layered magnetostrictive-piezoelectric structures are multifunctional due to their dual-responsiveness to mechanical and electromagnetic forces. Here, we discuss studies of magnetoelectric (ME) interactions in ferrite-lead zirconate titanate (PZT) and terfenol-PZT material couples. Key findings include: (1) the observation of a giant low-frequency ME effect in the layered systems; (2) data analysis based on our model for low frequency ME effects; (3) observation and theory of enhanced ME coupling at the electromechanical resonance (EMR); and (4) theory and measurements of microwave ME effects, at the ferromagnetic resonance of ferrites. The layered structures are potential candidates for sensors, gyrators and microwave devices. Low frequency sensors are feasible with excellent sensitivity to minute magnetic field variations. One could also realize composite based ferromagnetic resonance devices, such as resonators, filters and phase shifters with electric field tunability for use at 1–70 GHz.

Ferrite-Piezoelectric Layered Structures: Microwave Magnetoelectric Effects and Electric Field Tunable Devices

Studies on (i) microwave magnetoelectric (ME) interactions in ferrite-piezoelectric bilayers and (ii) electric field tunable ME signal processing devices are discussed. An electric field E applied to the bilayer produces a mechanical deformation in the piezoelectric, resulting in a frequency (δ f) or magnetic field shift (δ H) in the ferromagnetic resonance (FMR) absorption spectra for the ferrite. Bilayers of single crystal yttrium iron garnet (YIG) and lead zirconium niobate-lead titanate (PMN-PT) were studied. The strength of ME coupling A = δ H/E has been measured from FMR absorption profiles at 1–10 GHz for E = 0–10 kV/cm. Variation in δ f or δ H with E is found to be linear. A decrease in the ME coefficient is measured as the thickness of YIG film is increased. The fabrication and characterization of electric field tunable YIG/PMN-PT resonators are discussed.