Magnetic Microwave Devices Research Articles

La3+ ion doped Cd0.5C0.5LaxFe2-xO4 nanomagnetic materials for high-frequency device applications

The sol-gel self-combustion technique was applied to form Cd–Co-based La-doped (Cd0.5Co0.5LaxFe2-xO4) spinel ferrite nanoparticles. A series of six samples was synthesized by varying lanthanum content from x = 0.00 to 0.20. The structural characteristics of the prepared nanoparticles were carried out using X-ray diffraction (XRD) analysis. The (311) plane verified that the prepared nanomaterials are in the spinel phase in all observed XRD patterns. The crystallite size for each sample was determined using the Scherrer formula found in the 8.7–17.8 nm range, which is well correlated with the SSP model. The crystallite size decreased while the lattice constant increased from 8.38 to 8.45 Å with increasing La-content. The increasing trend in the bulk density and X-ray density has been analyzed with the effects of La3+ contents. In Fourier-transform infrared spectroscopy (FTIR), the high-frequency absorption band (υ1) was found from 522.15 to 541.06 cm−1, whereas the low-frequency band (υ2) varied from 419.80 to 414.31 cm−1. The surface morphology was carried out by scanning electron microscope (SEM), which positively correlated with XRD analysis. Impedance analyzer (IA) assisted in observing the variations in complex dielectric properties of the compound in the frequency range from 1 MHz to 3 GHz. The dielectric constant and impedance plots depicted that the nano ferrites have good dielectric properties in low-frequency regions due contribution of polarization. While conduction can be made possible in the high-frequency areas as observed through AC conductivity. The electric modulus revealed the relaxation phenomenon at high frequency due to the hopping of electrons at the octa and tetrahedral sites. The magnetic properties were investigated to study the impact of La3+ ion under the applied magnetic field from −15 to 15 kOe. The saturation magnetization, and magnetic remanence were found from 40.6 to 27.7 emu/g and 19.6 to 2.7 emu/g, respectively. The synthesized nanoparticles can be utilized for microwave applications and magnetic storage devices.

Tuning the Ferromagnetic Resonance Frequency of Microstructured Permalloy Film on Flexible Substrate

The importance of flexible ferromagnetic films in the application of flexible spintronic devices and microwave magnetic devices underscores the necessity for an in‐depth understanding of the dynamic magnetic properties of these films. In particular, it is crucial to comprehend the regulation of the ferromagnetic resonance (FMR) frequency of flexible ferromagnetic films. This work outlines the preparation of periodic permalloy microstrip arrays with stripe domain on flexible PET films and applies them to linearly tune the FMR. The high‐frequency optical branch (5.17 GHz) and low‐frequency acoustic branch (2.89 GHz) are observed in the direction perpendicular (x‐direction) and parallel (y‐direction) to the microstrip, respectively. The Young's modulus mismatch between the PET film and permalloy layer leads to the directional distribution of local tension. This results in the enhancement of the Ht (219.4 Oe) required for the in‐plane uniform precession on the PET film, compared to that on the Si substrate (181.6 Oe). By adjusting the width and thickness of the permalloy microstrip, Ht can be adjusted linearly on the PET film. This flexible ferromagnetic film with linear regulation of FMR frequency presents a new option for the future development of flexible microwave detectors and filters.

Sol-Gel synthesis of Ni-doped Zn-based spinel nanoferrites with structural and dielectric characterizations along with magnetic analysis

Ni-doped zinc ferrites (NixZn1−xFe2O4, 0.00 ≤ x ≤ 0.20 in steps of 0.05) were successfully synthesized using a sol-gel self-combustion method. The addition of nickel was aimed at modifying the high-frequency dielectric and magnetic properties of zinc ferrites. Various characterizations, including XRD, FTIR, LCR, and VSM analyses, were conducted to examine the crystal structure, absorption bands, dielectric properties, and magnetic properties of the compounds. XRD patterns revealed a monophasic cubic spinel structure with a preferred (311) plane orientation. The incorporation of Ni resulted in an increased crystallite size as determined by the Scherrer equation and Williamson-Hall method. The lattice parameters and unit cell volume decreased, while X-ray density increased. FTIR transmittance spectra confirmed absorption bands associated with tetrahedral and octahedral bonding. Dielectric parameters were studied across a frequency range of 1 MHz to 3 GHz, with the Maxwell-Wagner model used to explain the observations. Both components of the complex dielectric constant decreased with increasing frequency, indicating normal dispersion behavior of spinel ferrites. The electric modulus revealed relaxation mechanisms, while AC conductivity demonstrated conduction mechanisms. Magnetic properties were characterized using M-H loops measured via VSM. Increasing the Ni concentration led to higher saturation magnetization (Ms), magnetic remanence (Mr), and coercivity (Hc). Magnetic moments and anisotropy constants were calculated based on observed values of Ms and Hc. In summary, the nickel-doped zinc ferrites exhibited notable structural, magnetic, and dielectric properties, suggesting their potential utility in microwave and high-storage magnetic devices.

Micromorphology and uniaxial magnetic anisotropy of oblique-sputtered Ni80Fe20 films on periodically rippled Al2O3 substrates

Ni80Fe20 (NiFe) films were deposited on periodically rippled Al2O3 substrates by two different template oblique angle deposition (OAD) processes at various oblique deposition angles α (0° ≤ α ≤ 60°). The disparate in-plane uniaxial magnetic anisotropy (UMA) caused by the two template deposition processes of films was revealed by magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) measurements. The analysis of Transmission electron microscopy images indicated that this was related to the different micromorphology of the films due to the two template deposition processes. The angle between substrates’ ripple direction and the material flow incident direction would strongly influence the micromorphology and the induced in-plane UMA field of films. The values of the UMA field of these films can be much larger than those of the films oblique deposited on the plane Al2O3 substrates at the same α by choosing the template deposition direction. The results would help further modulate the UMA of magnetic films deposited on rippled substrates, which would be beneficial for the applications of these films in spintronic, magnetic memory and magnetic microwave devices.

Influence of the deposition conditions on the magnetic properties of Fe–Co–N thin films

(Fe0.65Co0.35)1-xNx thin films were prepared by magnetron sputtering under various deposition conditions. Their structure and magnetic properties were studied systematically. A coercivity as low as 1.5 Oe was obtained with an optimal N content by adjusting the nitrogen partial pressure fN. Furthermore, the films exhibited resonance frequencies higher than 1 GHz and adjustable dynamic magnetic properties. The damping coefficient α was maintained at a low level of approximately 0.01 under an appropriate fN (4–10%). These effects were attributed to the composition and microstructure of the films, which directly determined the static magnetic properties and dynamic parameters of the films. Furthermore, under different deposition conditions with the same fN, the deposition rate, film thickness, and deposition gas pressure played significant roles in improving the magnetic properties of the films. Therefore, Fe–Co–N films with adjustable anisotropy are expected to be a potential material for microwave magnetic devices. Moreover, systematic studies of Fe–Co–N films can help optimize the magnetic properties of Fe–Co-based films.

Functional nanostructures for bias-magnet-free and reconfigurable microwave magnetic devices

Recent demonstrations of the reconfigurable microwave properties based on patterned magnetic nanostructures without any external bias magnetic field have been reviewed. Two main design strategies for the nanostructures have been discussed. Firstly, self-biased nanomagnetic networks and multilayer structures that possess two different remanent magnetic states are exploited. Different remanent states are associated with distinct microwave properties and they are within a nanosecond time scale by using a simple field initialization scheme. The dipolar coupling field and the demagnetization field variations have been attributed to the origin of the tunable microwave responses. Secondly, magnetic skyrmions have been explored for tunable microwave properties. In this regard, skyrmion size which is directly related to its resonant modes has been controlled by placing it at different positions in an engineered nanostructure with varying edge repulsions. Finally, an outlook on the future directions and scopes of bias-free microwave devices have been discussed. It is also outlined that such devices have potential implications for the logic and magnonic technologies beyond their applications for microwave magnetic devices.

Effects of underlayer on structures and magnetic properties of Fe<sub>65</sub>Co<sub>35</sub> alloy films

Fe<sub>100-<i>x</i></sub>Co<sub><i>x</i></sub> (<i>x</i> = 30–40) alloys have the highest saturation magnetizations, 4π<i>M</i><sub>s</sub> ≥ 24 kG (1 G = 10<sup>–4</sup> T). Therefore, FeCo thin flms have been widely used in microwave magnetic devices. However, the as-deposited FeCo film has a large coercivity, which is attributed to the large saturation magnetostriction and high magneto-crystalline anisotropy<i>.</i> On the basis of maintaining high saturation magnetization, adding an appropriate underlayer is a simple and effective method to reduce the coercivity of the film and facilitate the magnetic field-induced in-plane uniaxial magnetic anisotropy. Since these kinds of films are used in a high-frequency environment, the eddy current loss in GHz band must be considered. For a certain film material, the thinner the film, the lower the eddy current loss is. However, at present, the thickness of ferromagnetic layer is generally tens of nanometers or even hundreds of nanometers, which will not help to suppress the eddy current loss at high frequency. In the present study, to obtain FeCo films with good soft magnetic properties and excellent high-frequency characteristics, Fe<sub>65</sub>Co<sub>35</sub> alloy films with a thickness of 13 nm and different underlayers (Cu, Co and Ni<sub>80</sub>Fe<sub>20</sub>) are prepared by magnetron sputtering. The effects of different underlayer materials and different NiFe underlayer thickness values on the structures and magnetic properties of FeCo films are studied. The results show that the introduction of underlayers can increase the in-plane uniaxial magnetic anisotropies of films, and the soft magnetic properties of films are significantly improved. The reason why the good soft magnetic properties can be achieved is attributed to the grain refinement, the dipolar interaction between layers, and the reduction of surface roughness. For different underlayer materials with the same thickness, NiFe underlayer can obviously improve the soft magnetic properties of FeCo films: the covercivity of easy axis is 23 Oe. By changing the thickness of NiFe underlayer, the dynamic magnetic properties of films can be adjusted. The resonance frequency changes from 3.13 GHz for NiFe(1 nm)/FeCo(13 nm) film to 2.78 GHz for NiFe(9.3 nm)/ FeCo(13 nm) film. For all NiFe/FeCo bilayer films, the real part of the permeability <i>μ′</i> at low frequency has a large value of 350–450, and the damping coefficient <i>α</i> shows a small value of 0.01–0.02. In addition, the smaller film thickness can reduce eddy current loss, which contributes to its application in high-frequency microwave magnetic devices.

Screen-Printable, Self-Biased SrM/PDMS Composites for Integrated Magnetic Microwave Devices

This work introduces a material and method for high-volume, low-temperature, screen printing of self-biased magnetic films made from a composite of M-type strontium ferrite SrFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> (SrM) particles and polydimethylsiloxane (PDMS). The magnetic particles are aligned under a dc magnetic field, while the PDMS is cured at 75 °C, making this fabrication process compatible with semiconductor and printed-circuit-board substrates. Aligned composites with estimated SrM particle volume percentages of 14 vol.%, 20 vol.%, and 27 vol.% are fabricated, as well as an unaligned 14 vol.% composite for comparison. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to examine the structure and composition of the composites. Furthermore, vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are performed to determine their dc and ac magnetic properties. Results show that the aligned composites have magnetic textures between 1.47 and 1.95, crystalline anisotropies between 1860 and 1960 kA/m, FMR frequencies of 45.5–45.9 GHz, and FMR linewidths between 3400 and 3500 Oe, indicating the potential for these materials in self-biased, non-reciprocal device applications. The analysis identifies that increased particle loading and better particle alignment may further improve these films by decreasing the linewidth.

Effects of substrate annealing on uniaxial magnetic anisotropy and ferromagnetic resonance frequency of Ni80Fe20 films deposited on self-organized periodically rippled sapphire substrates

Ni80Fe20 (NiFe) films have been deposited on self-organized sapphire substrates with periodical surface ripples formed by 2–10 h thermal annealing at 1400°C. By extracting static and dynamic magnetic parameters from magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) spectra, we quantified and analyzed the substrate annealing effects on the induced in-plane uniaxial magnetic anisotropy and ferromagnetic resonance frequency in these films. The study demonstrates that the uniaxial anisotropy of these NiFe films is strongly related to the annealing-time dependent substrate faceting and coarsening mechanisms. The uniaxial anisotropy field Hu changes from ~170 Oe to ~250Oe, and the maximum value of it is obtained in film on 8-h annealed substrate. The ferromagnetic resonance response and high frequency characteristics of films can be modulated by self-organized substrate is also confirmed. When external magnetic field is parallel to the direction of ripple, the ferromagnetic resonance frequency of films grown on the self-organized substrates is increased by ~0.3−1 GHz compared with that of reference film on plane substrate. This work would be helpful to design the high frequency properties of spintronic devices and micro-wave magnetic devices by utilizing self-organized substrates.

Influences of sintering atmosphere on the magnetic and electrical properties of barium hexaferrites

BaFe12O19 (BaM) hexaferrite has drawn increasing attention due to the high magneto-crystalline anisotropy and chemical stability, being a promising candidate in the field of magnetic microwave devices and magnetoelectric multiferroics. In this work, we studied the differences in microstructure and physical properties of BaM ceramics sintered in different atmospheres of nitrogen and air. It is found that N2 atmosphere does not significantly affect the morphology and magnetic properties of BaM, but dramatically reduces the resistivity from ∼ 1010 to ∼ 105 Ω·cm. By virtue of X-ray photoelectron and impedance analysis, the reduced resistance and increased permittivity value of the N2-sintered BaM were ascribed to the electron hopping mechanism caused by the formation of Fe2+ from Fe3+ ions.

Microwave Monolithic Devices Using Magnetic Hard-Soft Nanocomposite

Microwave magnetic devices have a major impact on the development of microwave technology. Ferromagnetic soft and hard ferrites are of special interest in order to make these devices. We have synthesized hard–soft nanocomposites of ferrites using barium hexaferrite (BaM)/yttrium iron garnets (YIG) at different ratios using the hydrothermal technique. The composites are deposited on a coplanar waveguide (CPW) by a medium-voltage electrophoresis method. The CPW devices are then tested for their notch-filter and phase shifter characteristics. The band-reject filter’s response over a wide frequency range and with applied magnetic fields (H) from 0 to 12 kOe was investigated. The attenuation increases with the increase in operating frequency having a tuning range: 1–30 GHz, bandwidth at 15 dB: 3.2 GHz and frequency tunability: 2.37 GHz/kOe. For phase shifter, the influence of magnetic material was studied for two frequency regions (at 9 and 30 GHz) one below and another above ferromagnetic resonance. In the high-frequency region (at 30 GHz), the optimal differential phase shift increased to 40°/cm for 0.5BaM/0.5YIG-based phase shifter at the highest field value.

Ferrites: magnetic materials as an alternate source of green electrical energy

Ferrites samples Mg1-xLixFe2O4 for x = 0.0, 0.1, 0.2, 0.3, were synthesized by solid-state sintering method. Detailed investigations were made on the structural, morphological, magnetic and electrical proprieties of these samples. A detailed investigation was performed on power generation of these samples and role of Li-doping has been discussed. The X-ray Diffraction (XRD) pattern confirms the spinel phase formation in samples without any impurity. It is observed from Scanning Electron Microscopy that average grain size of samples decreases with lithium doping in MgFe2O4. The saturation magnetization of MgFe2O4 (15.4 emu/g) is found to increase with Lithium percentage and maximum 39.3 emu/g for Mg0.7Li0.3Fe2O4 sample. Ferrites play a crucial role in magnetic recording, microwave magnetic devices and many applications in medical sciences. Recently, it was observed that ferrites can be an alternate source of green energy by inventing hydroelectric cell (HEC). The processes of water adsorption and dissociation on the metal-oxide surface, plays an important role in production of electricity in ferrites. When, water is sprayed on hydroelectric cell the thermodynamic driving force is responsible for the formation of stable metal-oxygen or metal-hydroxyl bonds. The reactivity of ferrite surface towards water is based on the interaction of these ions and the d orbital of the Fe atom. Due to this interaction, water dissociated in H3O+ and OH− ions and migrates toward silver and zinc electrodes respectively. A typical hydroelectric cell of 2 inch diameter produces 17.1 mA of peak current and 949 mV voltage with a maximum output power of 15.85 mW for Li = 0.2 doped MgFe2O4 sample.

A Strategy to Modulate the Bending Coupled Microwave Magnetism in Nanoscale Epitaxial Lithium Ferrite for Flexible Spintronic Devices.

With the development of flexible electronics, the mechanical flexibility of functional materials is becoming one of the most important factors that needs to be considered in materials selection. Recently, flexible epitaxial nanoscale magnetic materials have attracted increasing attention for flexible spintronics. However, the knowledge of the bending coupled dynamic magnetic properties is poor when integrating the materials in flexible devices, which calls for further quantitative analysis. Herein, a series of epitaxial LiFe5O8 (LFO) nanostructures are produced as research models, whose dynamic magnetic properties are characterized by ferromagnetic resonance (FMR) measurements. LFO films with different crystalline orientations are discussed to determine the influence from magnetocrystalline anisotropy. Moreover, LFO nanopillar arrays are grown on flexible substrates to reveal the contribution from the nanoscale morphology. It reveals that the bending tunability of the FMR spectra highly depends on the demagnetization field energy of the sample, which is decided by the magnetism and the shape factor in the nanostructure. Following this result, LFO film with high bending tunability of microwave magnetic properties, and LFO nanopillar arrays with stable properties under bending are obtained. This work shows guiding significances for the design of future flexible tunable/stable microwave magnetic devices.

Highly Stable In-Plane Microwave Magnetism in Flexible Li0.35Zn0.3Fe2.35O4(111) Epitaxial Thin Films for Wearable Devices.

With the advances in artificial intelligence and communication technologies, flexible microwave magnetic materials have become essential for flexible microwave detectors, wearable microwave sensors, and flexible spintronics. Here, a highly stable in-plane (IP) ferromagnetic resonance (FMR) and a tunable out-of-plane (OOP) FMR character are demonstrated in the flexible microwave magnetic Li0.35Zn0.3Fe2.35O4 (LZFO) (111) epitaxial thin films under external mechanical bending. Both the IP FMR line width and resonance field ( Hr) are basically unchanged when the sample was bent under an external tensile or compressive bending strain and deformation. However, the OOP FMR spectra (including Hr and absorption peak) could be tuned by mechanical bending, i.e., the LZFO sample possesses two OOP FMR absorption peaks at an external bending curvature. Meanwhile, excellent mechanical antifatigue and mechanical retention characteristics have also been obtained in the LZFO sample. The highly stable IP and the tunable OOP FMR spectra in the same LZFO sample with excellent mechanical antifatigue character have a promising prospect in microwave magnetic devices and flexible spintronics.

Optically-induced changes in magnetic properties of Fe2B/BiFeO3 heterostructure

Optical control of magnetic properties in exchange coupled photostrictive/ferromagnetic heterostructures is of great fundamental and technical interest for application in information storage, spintronic and microwave magnetic devices. In the present research, an optical modification of exchange bias field and magnetic properties of Fe2B/BiFeO3 heterostructure has been reported. A Fe2B/BiFeO3 bilayer and a BiFeO3 single-layer were deposited on (001)-SrTiO3 substrate by pulsed laser deposition technique. Magneto-optical hysteresis loops and x-ray diffraction pattern of the samples were recorded under light illumination with a wavelength of 405 nm at different intensities. Recorded hysteresis loops showed exchange bias coupling between ferromagnetic Fe2B and antiferromagnetic BiFeO3 layers. In addition, the results showed optically-induced changes in exchange bias and coercive fields. A critical point, in the variation of the exchange bias field with light intensity, was observed at 330 ± 10 mW/cm2. The behaviour of the exchange bias field was changed at this critical point with enhancement of the light intensity. Furthermore, the X-ray diffraction results indicated that light illumination led to an out of plane tensile strain in the BiFeO3 layer and this strain led to manipulation of the BiFeO3 magnetization. Therefore, the observed optically-induced changes can be related to the photo-induced strain in the BiFeO3 layer.

Reconfigurable magnetic and microwave properties of a ferrimagnetic-type artificial crystal

We have demonstrated a ferrimagnetic-type anti-parallel remanent state of rhomboid shaped nanomagnets of two different widths alternated in a dipolar coupled nanomagnetic array. The anti-parallel state is reconfigured to a parallel remanent state by using a simple field initialization process. Magnetic states were directly visualized using the magnetic force microscopy technique. Due to a variation of the stray field distributions for the two different remanent states, distinct dynamic responses are found using the broadband ferromagnetic resonance spectroscopy technique without applying any external bias magnetic field. Experimental observations were supported by the micromagnetic simulations. The results are important in the context of bias-field-free and reprogrammable microwave magnetic devices and creation of artificial ferrimagnetic crystals.

Thermomagnetization characteristics and ferromagnetic resonance linewidth broadening mechanism for Ca-Sn Co-substituted YIG ferrites

Yttrium iron garnet (YIG) ferrites own significant applications in microwave magnetic devices, such as circulators, isolators and filters. The excellent performance and reliability of these devices are strongly dependent on the saturation magnetization (Ms), ferromagnetic resonance (FMR) linewidth (ΔH), dielectric loss tangent (tan δε) and Curie temperature (Tc) of the garnet ferrites. Here, we fabricate Ca-Sn co-substituted Y3-xCaxFe5-xSnxO12 (x = 0.0, 0.1, 0.2, 0.3 and 0.4) ferrites using solid-state reaction method, and investigate the thermomagnetization characteristics of Brillouin function and FMR linewidth based on Néel model of ferrimagnetism and spin wave approach, respectively. This study clarifies the intrasublattice molecular-field coefficients ωaa, ωdd and intersublattice coefficients ωad = ωda. More importantly, we propose an accurate formula of Curie temperature Tc for garnet ferrites. Furthermore, Ca-Sn co-substitution can tailor the FMR linewidth based on the adjustment of anisotropy and the realization of densification. Finally, Y2.7Ca0.3Fe4.7Sn0.3O12 ferrite exhibits optimized magnetic property: 4πMs = 2073 Gs, ΔH = 42 Oe, Tc = 491 K.

Synthesis and microwave magnetic properties of magnetite nanowire arrays in polycarbonate templates

Abstract Magnetic nanowire arrays have potential applications in magnetic memory, microwave magnetic devices and many other fields. Spinel ferrite nanowire arrays exhibit a higher resistivity compared with metal counterparts; they also possess a strong shape anisotropy, such that they have high feasibility in microwave magnetic devices. Herein crystalline Fe 3 O 4 nanowire arrays were synthesized in polycarbonate porous membranes with pore sizes of 100 nm in diameter by one-step electrochemical deposition without heating. The phase structures, morphologies and magnetic properties were studied by XRD analysis, SEM and TEM observations and microwave magnetic measurements. The results showed that the as-prepared nanowires, characterized by polycrystalline phase structures, were uniform in size, with about 200 nm in diameter and 6–10 µm in length. Microwave magnetic properties of the arrays were characterized from microwave absorption parameters of the flip-chip on a microstrip line using a vector network analyzer (VNA). The ferromagnetic resonance (FMR) frequencies of ferrite arrays reached up to 25 GHz under a magnetic field of 9 kG, and more importantly it could be tuned in a wide frequency range by an external magnetic field. The results indicated that the Fe 3 O 4 nanowire arrays are promising absorbing microwave materials for flexible high-performance microwave devices.

Epitaxially grown BaM hexaferrite films having uniaxial axis in the film plane for self-biased devices

Barium hexaferrite (BaM) films with in-plane c-axis orientation are promising and technically important materials for self-biased magnetic microwave devices. In this work, highly oriented BaM films with different thickness and an in-plane easy axis (c-axis) of magnetization were grown on a-plane single-crystal sapphire substrates by direct current magnetron sputtering. A procedure involving seed layers, layer-by-layer annealing was adopted to reduce the substrate-induced strains and allow for the growth of thick (~3.44 μm) films. The epitaxial growth of the BaM film on sapphire was revealed by high-resolution transmission electron microscopy with dislocations being observed at the film-substrate interface. The orientation was also verified by X-ray diffraction and more notably, polarized Raman scattering. The magnetic properties and ferromagnetic resonant frequencies were experimentally characterized by a vibrating sample magnetometry and a frequency-swept ferromagnetic resonant flip-chip technique, respectively. The micron-thick BaM films exhibited a large remanence ratio of 0.92 along in-plane easy axis and a small one of 0.09 for the in-plane hard axis loop measurement. The FMR frequency was 50.3 GHz at zero field and reached 57.9 GHz under a magnetic field of 3 kOe, indicating that the epitaxial BaM films with strong self-biased behaviors have good electromagnetic properties in millimeter-wave range.

Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching

Electric-field modulation of magnetism in strain-mediated multiferroic heterostructures is considered a promising scheme for enabling memory and magnetic microwave devices with ultralow power consumption. However, it is not well understood how electric-field-induced strain influences magnetic relaxation, an important physical process for device applications. Here, we investigate resonant magnetization dynamics in ferromagnet/ferroelectric multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct strain states provided by electric-field-induced ferroelectric phase transition. The strain not only modifies magnetic anisotropy but also magnetic relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic Gilbert damping by electric field, which is attributed to strain-induced tuning of spin-orbit coupling. By contrast, a small but measurable change in extrinsic linewidth broadening is attributed to inhomogeneous ferroelastic domain switching during the phase transition of the PMN-PT substrate.