Microwave Magnetic Properties Research Articles

Strain engineering to tune the damping and magnetism in epitaxial spinel ferrite thin films by miscut substrate

Low-damping magnetic insulators like LiFe5O8 have gained considerable attention in recent years for their exceptional properties such as low energy loss and high gyromagnetic ratio, making them suitable in microwave and spintronic fields. However, due to factors such as crystalline quality and stress, the damping behavior of LiFe5O8 thin films falls below expectations. In this work, we utilize miscut substrate to modulate the structure and magnetic properties of LiFe5O8 films. We found that miscut angles can improve the crystalline quality of the film. However, a miscut angle of 6° resulted in a phase transition from tetragonal to orthorhombic in the LiFe5O8 phase. In particular, the out-of-plane ferromagnetic resonance linewidth of the orthorhombic LiFe5O8 (LFO) film was significantly reduced compared to that of the tetragonal LFO film on a non-miscut substrate, which could be attributed to the structural change. The orthorhombic LFO film also exhibited lower damping and a higher in-plane remanence ratio, indicating superior microwave magnetic properties. These findings suggest that miscut strain could be a viable method for improving the microwave magnetism of LFO films.

Strain engineering to tune the damping and magnetism in epitaxial spinel ferrite thin films by miscut substrate

Low-damping magnetic insulators like LiFe5O8 have gained considerable attention in recent years for their exceptional properties such as low energy loss and high gyromagnetic ratio, making them suitable in microwave and spintronic fields. However, due to factors such as crystalline quality and stress, the damping behavior of LiFe5O8 thin films falls below expectations. In this work, we utilize miscut substrate to modulate the structure and magnetic properties of LiFe5O8 films. We found that miscut angles can improve the crystalline quality of the film. However, a miscut angle of 6° resulted in a phase transition from tetragonal to orthorhombic in the LiFe5O8 phase. In particular, the out-of-plane ferromagnetic resonance linewidth of the orthorhombic LiFe5O8 (LFO) film was significantly reduced compared to that of the tetragonal LFO film on a non-miscut substrate, which could be attributed to the structural change. The orthorhombic LFO film also exhibited lower damping and a higher in-plane remanence ratio, indicating superior microwave magnetic properties. These findings suggest that miscut strain could be a viable method for improving the microwave magnetism of LFO films.

FeZrN Films: Static and Microwave Magnetic Properties

FeZrN Films: Static and Microwave Magnetic Properties

Microwave magnetic properties of twisting structure in artificial ferrimagnet Py/Gd multilayers

The noncollinear magnetic structure is attracting significant attention owing to its abundant characteristics as well as its potential applications in spintronic devices. In this work, the magnetic characteristics for an artificial ferrimagnetic Py/Gd multilayer system having the magnetic twisted state were investigated. With an increasing thickness (1.4 to 4 nm) of the Gd layer (tGd), the effective magnetization decreased initially until tGd = 2.5 nm and then increased, which was found to be induced by the change of magnetic twisted state due to antiferromagnetic coupling between Py and Gd. Moreover, the effective Gilbert damping factor was found to be completely opposite to the effective magnetization with increasing tGd. Our results provided detailed insights into the microwave magnetic properties of an artificial ferrimagnet with a noncollinear magnetic structure that provides alternative material in the application of spintronic devices

Broadband microwave magnetic and dielectric properties of (Mg0·6Cd0·4Co0·05Fe1·95O4)1-x+(MgTi2O4)x with x contents of 0.00, 0.06, 0.12, and 0.18 composites with low loss for high-frequency antennae

Two phase-based composites consisting of magnetic Mg0·6Cd0·4Co0·05Fe1·95O4 ferrite and dielectric magnesium titanate (MgTi2O4) were synthesized through a solid-state route. The structural and high-frequency magneto-dielectric properties of a series of (Mg0·6Cd0·4Co0·05Fe1·95O4)1-x+(MgTi2O4)x with x contents of 0.00, 0.06, 0.12, and 0.18 were studied. The phase structure was examined via X-ray diffraction (XRD), the results indicated the occurrence of both spinel MgTi2O4 and MgFe2O4 phases in various composites. Meanwhile, grain size and bulk density were lowered with the introduction of MgTi2O4, which also significantly weakened magnetic properties with decreased saturation magnetization (Ms) from 43.05 emu/g to 20 emu/g and coercivity (Hc) from 67.02 Oe to 3.35 Oe. In addition, the real permeability (μʹ) decreased and permittivity (ε′) increased with increasing MgTi2O4 content over the wide frequency range of 0.5–5 GHz. Finally, a low order of magnitude (tan δμ ≈ 10−1 to 10−2 and tan δε ≈ 10−2 to 10−3) was obtained for all composites. These results demonstrated that the synthesized composites were expected to be an ideal candidate for high-frequency antenna loading materials.

Плёнки FeZrN: статические и СВЧ магнитные свойства

The phase-structural state, magnetic structure parameters, static and microwave magnetic properties of Fe81 – 74Zr2 – 5N17 – 21 films prepared by reactive magnetron deposition were studied. As the Zr and N contents increase, the film structure changes from, so-called, mixed structure (grain size 3 – 6 nm of nanocrystalline α-Fe(Zr,N) + fcc nitride) to amorphous one. The film magnetic structure parameters (effective anisotropy field of stochastic domains D1/2〈Ha〉 = 11.8 ± 8 Oe and effective local anisotropy field D1/2Ha = 880 ± 700 Oe), saturation magnetization Ms (1.8 ± 0.3 T), coercive field Hc (11 ± 2 Oe), and the real permeability µ′ (80 ± 30), retaining its value at frequencies up to 3 GHz, were determined. The values of the initial permeability µ0 (70 ± 21) obtained from the hysteresis and the real permeability µ′ (80 ± 30) obtained from microwave measurements are in good agreement. The correlation between the static magnetic properties, the stochastic magnetic structure parameters and the real permeability µ′ was considered. There is no any sign on ferromagnetic resonance in the studied frequency range. However the Acher’s coefficient value (less than 0.38) for this frequency range indicates the possibility of ferromagnetic resonance at higher frequencies.

Mechanistic study of the effect of Ca–Sn co-doping on the microwave dielectric properties and magnetic properties of YIG

To investigate the crystal structure, electrical properties, and magnetic properties of Ca–Sn co-doped Y3-xCaxFe5-xSnxO12 (x = 0.00–0.25 in steps of 0.05), solid-state reaction experiments, first principles calculations, and complex crystal bonding theoretical calculations were performed. The relative permittivity (εr) is strongly correlated with the average bond ionicity when Ca2+ is added. Furthermore, appropriate Sn4+ substitution significantly lowers the dielectric loss (tanδε) associated with the lattice energy. The right amount of Ca–Sn co-doping can change the saturation magnetization (4πMS) and improve the microscopic morphology of YIG, lowering the ferromagnetic resonance linewidth (ΔH) of YIG. The optimized microwave dielectric and magnetic properties are as follows: εr = 14.7, tanδε = 4.15 × 10−4, 4πMS = 1680 G, and ΔH = 53 Oe for Y2.8Ca0.2Fe4.8Sn0.2O12 sintered for 6 h at 1425 °C. Based on this material, a simple 3D model of a strip-line circulator with an insertion loss of less than 0.3 dB at each port and isolation greater than 20 dB in the 10–12 GHz range was developed, indicating the potential of the material for microwave high-frequency components such as circulators.

Magnetic and microwave absorption properties of Ni0.6Zn0.4Fe2O4 /SrFe12O19 composites

In this work, pure Ni0.6Zn0.4Fe2O4 (NZFO) and Ni0.6Zn0.4Fe2O4/SrFe12O19 (NZFO/SFO) composites have been prepared by solid-state reaction method, their microwave absorbing and magnetic properties have been systematically investigated. The samples were characterized by XRD, FTIR, SEM, SQUID and VNA. The results show that the maximum reflection loss and bandwidth (RL < −10dB) of Ni0.6Zn0.4Fe2O4 ferrite are −36.25 dB and 5.5 GHz, but the bandwidth below −10dB is divided into two parts. In order to obtain a continuous bandwidth below −10dB for Ni0.6Zn0.4Fe2O4 ferrite, strontium ferrite is added to adjust the microwave absorption performance. When the mass ratio of Ni0.6Zn0.4Fe2O4 ferrite and SrFe12O19 ferrite is 1:2 and the thickness is only 1.8 mm, NZFO/SFO composite exhibits excellent microwave absorbing properties. The maximum reflection loss is −25.9 dB, and the absorption bandwidth for RL < −10dB was 6.4 GHz in the frequency range from 11.6 GHz to 18 GHz, covering the entire x-band. The results show that the improvement of the microwave absorption performance of NZFO/SFO composites is related to the parameters such as interface polarization, dipole polarization, natural resonance, eddy current loss, conduction loss and impedance matching. The ideal experimental results show that the NZFO/SFO absorbent has the characteristics of strong absorption, wide bandwidth, and thin layer, and has broad application prospects in civilian and military fields.

Detailed microwave absorption performance of BaFe12O19 nano-hexaplates with a large variety of thicknesses

We successfully prepared BaFe12O19 (BaM) nano-hexaplates using the co-precipitation method followed by heat treatment. The hexaplate-like grain size varied in the range of 50–200 nm, while its crystalline size was ∼46 nm. Before investigating microwave absorption, structural and magnetic properties were studied by x-ray diffraction, Raman scattering, and a vibrating sample magnetometer. The structural studies showed a pure phase of BaM, while the magnetic studies revealed a ferro/ferrimagnetic behaviour with M s = 59.93 emu g−1, M r = 32.49 emu g−1, and H c = 5.16 kOe. Microwave dissipation features were systemically investigated for device thickness of 0.25–10 mm with a measured frequency range of 2–16 GHz. The study showed that the BaFe12O19 sample could absorb more than 99.9% of the incident microwave in the 12–14 GHz frequency range for 6.5 mm thickness. The effective absorption bandwidth was also fairly large, as ∼3 GHz in this frequency range. The microwave dissipation features of BaM in this work were better than pure BaM ones in other studies and relatively comparable with BaM-based microwave absorbers. The magnetic loss originated from natural resonance, while the dielectric loss resulted from multi-interface, interface, and dipolar polarization. Overall, the BaFe12O19 sample in this study could be used as a promising microwave absorber in the Ku waveband.

Investigation of nickel and manganese substitutions on the microwave absorption and magnetic properties of hexaferrite strontium nanoparticles prepared by sol–gel auto-combustion method

Investigation of nickel and manganese substitutions on the microwave absorption and magnetic properties of hexaferrite strontium nanoparticles prepared by sol–gel auto-combustion method

Investigating the effect of Pr doping BiFeO3 on the microwave absorption and magnetic properties

Bi1-xPrxFeO3 material with perovskite structure was prepared using organic tartaric acid-assisted sol–gel self-propagating combustion method to obtain high-efficiency microwave absorption materials. The influence of the introduction of Pr on dielectric properties and permeability was further studied. After 15% Pr introduced, the lowest reflection absorption loss reaches –32.34 dB, but the absorption bandwidth is only 2.25 GHz. When Pr is 5%, the lowest reflection absorption loss value of −27.31 dB is obtained, and the effective bandwidth which below −10 dB is 3.41 GHz. The structural changes in the process of Pr replacing Bi were analyzed to explore the properties of BPFO perovskite. The influence of strong interaction force, residual magnetization, and natural resonance of ceramic nanoparticles on microwave absorption performance was explored. This work supplies a reliable candidate material for making up electromagnetic attenuation ceramic materials with excellent properties.

Cylindrical nanowire arrays: From advanced fabrication to static and microwave magnetic properties

This article reviews information on arrays of cylindrical magnetic nanowires grown electrochemically inside ordered nanoporous alumina membranes, summarizing some of the most relevant aspects about the advanced synthesis of nanowires and their overall static and microwave magnetic properties. The electrochemical details for the preparation of templates with well-defined hexagonal ordering are addressed focusing on the different anodization methods including mild, hard, pulsed or anodization of aluminum rods. A section follows on the growth of metallic nanowires, either as single element (i.e., Fe, Ni, Co), alloys (i.e., CoFe, CoNi, FeNi) or modulated in composition (i.e., Ferromagnetic/Metal). The static magnetic properties as anisotropy, coercivity and magnetostatic interactions are overviewed with particular emphasis on the influence of magnetocrystalline anisotropy and on the temperature dependence of those properties. The last section is devoted to the ferromagnetic resonance of nanowire arrays of different composition. The dependence of microwave absorption on the orientation of applied field is also a useful tool to determine the magnetic anisotropy parameters and the significance of magnetostatic interactions. The magnetization easy axis can be switched from the nanowire direction to the plane of the membrane as the nanowire filling factor increases or at a compensation temperature, in both cases it derives from the energetic balance of anisotropy and magnetostatic interactions among nanowires. A final subsection is devoted to the spin waves resonance spectra, and the perspectives of applications making use of microwave properties. We expect the article can be useful for researchers interested on the topic and provide a wide overview on the matter to those starting a new research line.

Synthesis of a hollow-structured flower-like Fe3O4@MoS2 composite and its microwave-absorption properties.

In order to realize the characteristics of new types of wave-absorbing materials, such as strong absorption, broad bandwidth, low weight and small thickness, a hollow-structured flower-like Fe3O4@MoS2 composite was successfully prepared by simple solvothermal and hydrothermal methods in this paper. The structural properties were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Besides, the microwave properties and magnetic properties were measured using a vector network analyzer and via a hysteresis loop. SEM and TEM images revealed that MoS2 nanosheets grew on the surface of hollow nanospheres. The results showed that the composite exhibited excellent absorbing property. When the molar ratio of Fe3O4 and MoS2 was 1 : 18, the minimum reflection loss value reached −49.6 dB at 13.2 GHz with a thickness of 2.0 mm and the effective absorption bandwidth was 4.24 GHz (11.68–15.92 GHz). Meanwhile, the effective absorption in the entire X-band (8–12 GHz) and part of the C-band (4–8 GHz) and Ku-band (12–18 GHz) could be achieved by designing the sample thickness. In addition, the hollow structure effectively reduced the density of the material, which was in line with the current development trend of absorption materials. It could be predicted that the hollow core–shell structure composite has a potential application prospect in the field of microwave absorption.

Study of the Static and Microwave Magnetic Properties of Nanostructured BaFe12−xTixO19

The effect of Ti substitution on the microwave and magnetostatic properties of nanostructured hexagonal BaFe12−xTixO19 ferrite composites is studied. The microwave permeability is measured in the frequency range of 0.1–22 GHz by a coaxial technique. An analysis of the magnetostatic data is made by the law of approach to saturation. The ferrimagnetic resonance frequencies calculated from the magnetostatic data are consistent with those obtained from the microwave measurements. The natural ferrimagnetic resonance frequencies are located in the frequency range of 15 to 22 GHz, depending on the substitution level x. An increase in the amount of substitution elements results in a low-frequency shift of the ferrimagnetic resonance frequency for samples with x &lt; 1. With x rising from 1 to 2.5, the resonance frequency increases. The results of the study demonstrate that the tailored optimization of the nano-structure of a functional material is a robust tool to fine-tune its microwave magnetic properties. The ferrites under study are promising materials to be applied as functional coatings intended to control electromagnetic interference in microwave devices.

Evaluation of the size and medium effects on the microwave absorbing, magnetic, electromagnetic shielding, and optical properties using CuCo2S4 nanoparticles

The aim of this study was preparation of CuCo2S4 nanostructure using a hydrothermal method and investigation of the temperature and pressure effect on the morphology, optical, magnetic, and microwave characteristics. Furthermore, urea was applied as a precursor and its influence on the CuCo2S4 properties were scrupulously dissected. On the other hand, polystyrene (PS) and polyvinylidene fluoride (PVDF) were used to evaluate the medium effect on microwave attenuation. The prepared nanoparticles were assessed by the X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), diffuse reflection spectroscopy (DRS) analyses. The analyses confirmed the effect of temperature, pressure, and urea on morphological, optical, and magnetic features as well as illustrated that pure CuCo2S4 nanoparticles (NPs) have been synthesized. Eventually, a vector network analyzer (VNA) demonstrated the significant microwave absorbing characteristics of the samples and confirmed that shape and medium play a vital role, paving the way for microwave attenuation. The maximum reflection loss (RL) of NPs prepared at 180 °C/PS composite was 79.37 dB at 15.42 GHz, while NPs prepared at 200 °C/PVDF achieved an efficient bandwidth as wide as 7.32 GHz (RL < −10 dB) and 2.66 GH (RL < −20). Interestingly, NPs prepared at 200 °C and treated NPs/PS illustrated total shielding effectiveness (SET) > 15 dB in entire x and ku-band frequency.

Microwave synthesis and magnetic properties of bismuth ferrite nanopowder doped with cobalt

A technique for the synthesis of bismuth orthoferrite nanopowder doped with cobalt ions activated using microwave radiation is proposed. Exposure to microwave radiation followed by ultrasonic treatment of the synthesized BiFeO3 samples using sodium hydroxide as a precipitant makes it possible to obtain spherical BiCoxFe1-xO3 particles with a narrow particle-size distribution in the range of 35–60 nm. Bismuth ferrite doped with cobalt ions has a considerably higher magnetization and magnetic susceptibility than an undoped BiFeO3.

Enhanced structure and microwave magnetic properties of MgZn ferrite by Cd2+ ion substitution for LTCC applications

Due to its excellent magnetic properties, MgZn ferrite is a nearly optimal material for low temperature co-fired ceramic (LTCC) phase shifter applications. In this study, low temperature co-fired Mg0.8Zn0.2-xCdxFe2O4 ferrites (x = 0.00–0.10, with increments of 0.02) were synthesized using a solid-state method with the aid of 2.5 wt% BBSZ (33%mol Bi2O3-21%mol B2O3-11%mol ZnO-35%mol SiO2) glass sintering. The effects of the Cd2+ ions on phase formation, microstructure, magnetic permeability, and gyromagnetic properties were investigated. The results indicated that a suitable amount of Cd2+ ion substitution did not change the phase formation of MgZn ferrite. However, with further increases of the Cd2+ ion content, the superfluous Cd2+ ions and Fe3+ ions formed CdFe2O4, which affected the microstructure, density and magnetic properties of the samples. More specifically, when x = 0.04, Mg0.8Zn0.16Cd0.04Fe2O4 ferrite, sintered at 920 °C, showed excellent magnetic permeability (μ'~56.6 @1 MHz–20 MHz) and had a high cut-off frequency (~100 MHz). Furthermore, the ferromagnetic resonance line widths (ΔH) were measured as a function of the Cd2+ substitution at 9.56 GHz, and the relationships between ion occupancy and microstructure were also discussed. A narrow ΔH (~228.2 Oe) can be obtained by adding an optimal amount of Cd2+ ions. These observations indicate that MgZn ferrites with a suitable amount of Cd2+ ions are promising candidate materials for LTCC electronic device applications.

Study of the microstructure and microwave magnetic characteristics of Ti-doped Li–Zn ferrite

The effects of sintering temperature and Ti substitution on the microstructure and microwave magnetic properties of Li–Zn ferrites prepared by a ceramic process were investigated. The pure spinel phase of the specimens was observed from X-ray diffraction patterns. The densification and grain growth were enhanced due to the increase of sintering temperature. The grain growth had negative effects on the squareness ratio of high-porosity specimens. Moreover, the magnetic anisotropy constant (K1) was estimated and discussed. The ferromagnetic resonance linewidth (ΔH) values measured at the Ku-band decreased by 18% owing to improved microstructure. The contributions of other linewidths to ∆H were estimated.

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.

Flexible Lithium Ferrite Nanopillar Arrays for Bending Stable Microwave Magnetism.

Recent development in magnetic nanostructures has promoted flexible electronics into the application of integrated devices. However, the magnetic properties of flexible devices strongly depend on the bending states. In order to realize the design of new flexible devices driven by an external field, the first step is to make the magnetic properties insensitive to the bending. Herein, a series of LiFe5O8 nanopillar arrays were fabricated, whose microwave magnetic properties can be modulated by tuning the nanostructure. This work demonstrates that nanostructure engineering is useful to control the bending sensitivity of microwave magnetism and further design stable flexible devices.