Narrow Ferromagnetic Resonance Linewidth Research Articles

Magneto-optical epitaxial bismuth-substituted yttrium iron garnet thin films on a diamagnetic substrate for low temperature applications

The uprising interest in the integration of the magneto-optical iron garnets into the field of quantum information processing imposes requirements for the damping parameter and optical properties at low temperatures. Typically, high quality iron garnet films are mostly grown epitaxially on the paramagnetic substrates that have rare-earth elements in its composition, which leads to an increase of their magnetic damping at temperatures below 100 K. Here, we epitaxially grew magneto-optical ferromagnetic garnet films on a diamagnetic yttrium scandium gallium garnet substrate to demonstrate narrow ferromagnetic resonance (FMR) linewidth at temperature range from 300 K to 4 K. The maximum Faraday angle measured at wavelength of 660 nm is ΘF = 0.34 ⋅103 deg/cm at 65 K. The FMR linewidth of the iron garnet film gets slightly larger as temperature decreases, but still remains at a level of 35 Oe at 4 GHz even at 4 K. The investigated iron garnet thin films grown on diamagnetic substrates can be successfully implemented in low-temperature technological applications that require low damping and high magneto-optical response.

Investigation of crystal structure, Raman spectroscopy and magnetic properties of La-Zn substituted oriented M-type hexagonal barium ferrites

M-type hexagonal barium ferrite (BaM) has received much attention in the application of self-biased microwave devices because of its large anisotropic field (Ha) and high saturation magnetization (Ms), but the increased Ha inevitably increases the microwave magnetic loss of the device. In addition, the devices need to have a high Ms for high frequency applications. To address these issues, we used La3+ and Zn2+ instead of Ba2+ and Fe3+ ions to modulate the Ha and Ms of BaM, respectively. Ba1-yLayFe12-xZnxO19 (x=y=0.1–0.5) M-type hexagonal ferrite was synthesised by conventional solid-phase methods. The La-Zn co-substituted BaM samples were shown to be purely single phase by X-ray diffraction (XRD) analysis. The lattice parameters, specific surface area, crystallite size, dislocation density and microstrain of the samples were also calculated using the XRD data. Furthermore, La3+ and Zn2+ can not only modulate the sample Ha and Ms between 10,214–12,102 Oe and 62.94–78.23 emu/g, respectively, while making the sample more denser. At x=0.3 BaM detects relatively satisfactory properties: large Ms=63.12 emu/g, suitable Ha=10,214 Oe and Hc=2248.87 Oe, high Mr/Ms=0.832 and narrow ferromagnetic resonance linewidth (= 903 Oe), which provide good candidates for next-generation self-biased and low-loss microwave wave devices.

Ca-Sn co-substituted BiIn-YIG ferrite with narrow FMR linewidth for microwave device application

The requirements for improving the performance and miniaturizing microwave devices have led to higher demands for the yttrium iron garnet (YIG) ferrite materials. To achieve YIG ferrite materials with narrow ferromagnetic resonance (FMR) linewidths, and stable magnetic and dielectric properties, Ca-Sn co-substituted YIG samples with the composition Bi0.4Y2.6-xCaxFe4.65-xIn0.35SnxO12 were synthesized via solid-state sintering at 1230 °C. The microstructural, magnetic, and dielectric properties of the samples were systematically tested and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance analyzer, vibrating sample magnetometry (VSM), and ferromagnetic resonance (FMR). The results indicate that the co-substitution of Ca2+ and Sn4+ ions did not alter the crystal structure of YIG ferrites, and effectively improved the microstructure and performance of the material. When the doping concentration (x) was 0.40, the obtained sample exhibited the narrowest FMR linewidth (ΔH = 43.46 Oe) and excellent magnetic and dielectric properties (4πMs = 1555.68 G, ε′ = 14.12 @ 100 MHz). The material proposed in this study demonstrates significant potential for applications in microwave devices.

The epitaxial iron-yttrium garnet films with homogeneous properties and narrow FMR line width

The growth of iron-yttrium garnet Y3Fe5O12 (YIG) films with of 1...15 μm thicknesses on single-crystal substrates of gallium-gadolinium garnet Gd3Ga5O12 (GGG) was carried out using the method of liquid phase epitaxy (LPE). The influence of the composition and mass of the charge, the temperature regimes, the rates of movement and the substrate rotation on the films parameters were studied. The layered structure caused by the heterogeneity of the chemical composition in the film thickness was determined and studied The dependence of the degree impurity of Pb2+ and Pt4+ ions in YIG films and their influence on the ferromagnetic resonance (FMR) line width ∆H on the films growth conditions was investigated. It’s shown that in order to obtain by the LPE method the series of defect-free films with low magnetic losses and reproducible parameters, it’s necessary to use melt-solutions of large mass (6...12 kg) and apply their additional mixing during the growth process.

Effect of annealing temperature on the properties of BaFe12O19 thin films deposited on GGG (1 1 1) substrates by pulsed laser deposition

In this work, BaFe12O19 thin films with perpendicular magnetic anisotropy have been deposited on GGG (111) substrates by pulsed laser deposition in an oxygen atmosphere using a KrF excimer laser. The effects of annealing temperature on the microstructural, magnetic, and microwave properties of BaFe12O19 thin films were investigated. It is found that the properties of BaFe12O19 films are very sensitive to the annealing temperature, and excellent films are obtained when the annealing temperature is above 900 °C. X-ray diffraction diagrams show that films annealed at higher temperatures (≥950 °C) have better crystallization and higher perpendicular orientation. Atomic force images show the surface morphology of annealed films above 900 °C to be very smooth, with a minimum roughness of 0.754 nm. Hysteresis loops reveal that the saturation magnetization of the films annealed above 1000 °C is similar to that of bulk barium ferrite, and the maximum value of 4676 Gs is obtained at 1100 ℃. The anisotropy field increases with the increase in annealing temperature, reaching a maximum of 18.0 kOe at 1050 °C. The remanence ratio and saturation magnetization also show an upward trend as the annealing temperature rises. The film annealed at 1100 °C shows a very narrow ferromagnetic resonance linewidth with a width of about 256 Oe at 39 GHz. And the ferromagnetic resonance linewidth of the films decreases as the temperature rises, which means that films annealed at higher temperatures have less microwave loss.

Microstructure and gyromagnetic properties of low-sintered LiZnTi ferrite doped with nano-LiZn and V2O5 additives

In this study, nanoparticles of LiZn ferrite (nano-LiZn, 0.0–10.0 wt. %) fabricated via the sol-gel method and V2O5 particles were added into a Li0.43Zn0.27Ti0.13Fe2.17O4 (LiZnTi) ferrite to realize low temperature sintering. The effects of the nano-LiZn ferrite addition on the crystalline phase formation, microstructure, and magnetic properties of LiZnTi ferrite were systematically investigated. X-ray diffraction results reveal that the LiZnTi ferrite doped with nano-LiZn and V2O5 additives present a pure spinel structure, which can be explained by liquid phase of V2O5 and spinel structure of nano-LiZn, as revealed by high-resolution transmission electron microscopy and selected area electron diffraction data. Scanning electron microscopy images show that the addition of nano-LiZn leads to a change in the microstructure, with the grains becoming uniform and dense. Additionally, the variation in the saturation magnetization (Ms) depends on the LiZn content. In particular, Ms increases with increasing LiZn content from 2.0 to 10.0 wt. %. Finally, the LiZnTi ferrite doped 4.0 wt. % nano-LiZn and 0.60 wt. % V2O5 possesses a narrow ferromagnetic resonance linewidth of 197 Oe, a reduced coercivity of 192.6 A/m, and an improved bulk density of 4.73 g/cm3.

Structural and magnetic properties of Y3(GaAlFe)5O12 liquid-phase epitaxy films with low ferromagnetic resonance losses.

Ultra-thin rare earth iron garnet (RIG) films with a narrow ferromagnetic resonance (FMR) line width and a low damping factor have attracted a great deal of attention for microwave and spintronic applications. In this work, 200 nm Y3(GaAlFe)5O12 garnet (GaAl-YIG) films were prepared on gadolinium gallium garnet (GGG) substrates by liquid-phase epitaxy (LPE) with low saturation magnetization. The microstructural properties, chemical composition, and magnetostatic and dynamic magnetization characteristics of the films are discussed in detail. According to the structural analysis, these films exhibit a low surface roughness of less than 0.5 nm. The GaAl-YIG films show an obvious temperature dependence of lattice parameter and strain state, and the film's parameter is perfectly matched with that of the GGG substrate at 810°C. There is a clear variation in the Pb level, which brings about a gradual enhancement of the coercivity and a diminution of the squareness ratio of magnetic hysteresis loops as the growth temperature is reduced. Slight changes in surface roughness, strain condition and content of Pb induce the FMR line width and damping factor to vary on a small scale. The line width is less than 10.17 Oe at 12 GHz and the damping factor is of the order of 10-4. All these properties demonstrate that these ultra-thin GaAl-YIG films are of benefit for the development of devices operated at lower frequencies and in lower fields.

Emerging magnetodielectric materials for 5G communications: 18H hexaferrites

With the rapid development of 5G technologies, it is crucial to seek magnetodielectric materials with high permeability and permittivity, low magnetic and dielectric losses, and high cutoff frequency over the sub-6 GHz frequency bands. Due to limited resonant frequency and large natural resonance linewidth, conventional microwave ferrites and their composites do not meet these requirements. Here, the microwave properties and their temperature dependence of a unique type of hexaferrites, Mg-Zn 18H hexaferrite (Ba5Mg2−xZnxTi3Fe12O31), are reported. Polycrystalline Mg-Zn 18H hexaferrite exhibited an extremely low damping coefficients (α = 0.1-0.2), remarkably low magnetic loss (tan δm = 0.06), excellent thermal stability of the damping coefficient (Δα/ΔT = 0.0004 K−1), and a narrow ferromagnetic resonance (FMR) linewidth (ΔH = 486–660 Oe). Moreover, Mg-Zn 18H hexaferrite possessed significant enhancement in the figure of merit (FOM = μ'Qf) compared to conventional microwave ferrites and their composites. When employed as the substrate of a 3.6-GHz patch antenna, Mg-Zn 18H hexaferrite demonstrated significant advantages for miniaturization (∼5 ×) and bandwidth improvement (∼50–110%) over conventional dielectric substrates. These results represent the best magnetic performance among the microwave ferrites reported at the S band and reveal the great technological value and commercial potential for 5G communications.

Spin transport properties of Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12 </sub>thin films prepared by spin coating

Yttrium iron garnet (YIG), as a room temperature ferrimagnetic insulator with low damping and narrow ferromagnetic resonance linewidth, has been the research hotspot in spintronics because of its spin transport properties. Bi is one of the most common doping elements used in YIG, and some researches have proved that it can tune the magnetic properties of YIG. Previous studies of Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> thin films focused on the evolutions of their structures, morphologies, and magnetic characteristics. Yet, the effects of Bi<sup>3+</sup> substitution of Y<sup>3+</sup> on spin transport in YIG thin films have not been systematically studied. The regulation of YIG spin transport by doping is expected to provide a new idea for the spintronics exploration of Pt/YIG system. In this work, we prepare a series of Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> films with different doping ratios by spin coating. And we investigate the effects of Bi<sup>3+</sup> on morphology, structure and spin transport properties of YIG films. The results show that Bi doping does not change the crystal structure of YIG. The absorption of the film increases and the bandgap decreases with the increase of doping ratio. The X-ray photoelectron spectroscopy (XPS) indicates the co-existence of Bi<sup>3+</sup> and Bi<sup>2+</sup>. The regulation of Bi doping on spin transport is reflected in the fact that the magnon diffusion length of Bi<i><sub>x</sub></i>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> films is significantly smaller than that of pure YIG films. Meanwhile, we find that the obvious spin Hall magnetoresistance can still be detected in the Pt/Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> heterostructure, and the amplitude is the largest when <i>x</i> = 0.3.

Enhanced FMR linewidth and magnetic properties of In3+-doped YIG ferrite materials for microwave devices applications

Herein, In-doped Y3Fe5-xInxO12 (x = 0.00–0.75 with a step of 0.15) material was fabricated via solid state route. Mixed powders were sintered at 1450 °C for 6 h in the air. The microstructure and magnetic properties were examined by X-ray diffraction (XRD), Scanning electron microscope (SEM), Raman spectra, Vibrating sample magnetometer (VSM), and ferromagnetic resonance (FMR). Results show that In3+ ion substitution did not change crystal type of YIG ferrite and increased bulk density. SEM observations indicate that doped In3+ ion not only entered the crystal but also affected the grain size. According to VSM results, by increasing In3+ ion content from x = 0.00 up to x = 0.75, saturation magnetization (Ms) enhanced from 25.8 emu/g to 28.21 emu/g (x = 0.45). Then, Ms declined to 19.33 emu/g. Furthermore, narrowest FMR line width (ΔH) was obtained (ΔH = 36.7 Oe at x = 0.45) based on In-doping. The proposed material has potential for use in antenna or high-frequency applications in phase shifter, circulator, and microwave high-frequency components.

Low dielectric loss and narrow FMR linewidth of Ca-Ge co-substituted YInIG ferrites for microwave device application

Recently, the yttrium iron garnet (Y3Fe5O12, YIG) ferrite material is widely applied in the microwave devices due to its good frequency stability and loss magnetic loss. In this work, Y3−xCaxIn0.6GexFe4.4−xO12 (x = 0.0–0.6 with a step of 0.1) materials were synthesized by the conventional solid-state reaction method. The effects of Ca-Ge co-substitution on the microstructural, dielectric and magnetic properties of YInIG materials were investigated. Ca-Ge co-substitution did not change the phase formation of YInIG ferrite, and enhanced dielectric and magnetic properties of samples. The high saturation magnetization (4πMs), low dielectric constant (εr), low dielectric loss (tanδε), small coercivity (Hc) and narrow ferromagnetic resonance (FMR) linewidth (ΔH) were obtained for high frequency microwave device application. When substituted content x = 0.4, Y2.6Ca0.4In0.6Ge0.4Fe4O12 has the optimum microwave properties: εr = 13.884@10.8 GHz, tanδε = 3.053 × 10–4, Hc= 22.75 Oe, 4πMs = 1226.83 Gs, ΔH= 19.3 Oe. The narrow FMR linewidth and low loss dielectric loss of the investigated samples suggested the possible use of these materials in high frequency applications.

Synergy effects between Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and CuO-Bi2O3 mixtures in low-temperature sintered LiZnTi ferrites with enhanced gyromagnetic and microwave dielectric properties

Promoting grain growth and optimizing microstructure are valid strategies for enhancing gyromagnetic and microwave dielectric properties of low-temperature sintered ferrite materials. Here, a modified low-temperature sintering technique was attempted for the synthesis of LiZnTi ferrites that have compact microstructure and improved performances. Trace amounts of CuO-Bi2O3 mixtures (0.50 wt%) were adopted as sintering additives to promote grain growth and to reduce the sintering temperature. Meanwhile, Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles (∼21.9 nm) were synthesized using a sol-gel auto-combustion method and were used to optimize the microstructure and to restrain abnormal grain growth. XRD Rietveld refinement and SEM images revealed that uniform and dense LiZnTi ferrites with single-phase spinel structure were obtained. Results demonstrated that co-doping of Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and CuO-Bi2O3 mixtures allows low-temperature sintering (900 °C) to be achieved and also promotes grain growth and densification. In particular, LiZnTi ferrites that were modified with 5.00 wt% Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and 0.50 wt% CuO-Bi2O3 sintering additives exhibited narrow ferromagnetic resonance linewidth (ΔH, ∼145 Oe) and low dielectric loss tangent (tanδε, ∼2.45 × 10−4) at ∼9.50 GHz, high saturation flux density (Bs, ∼364 mT), and high squareness ratio (Br/Bs, ∼0.89). Such a modified sintering technique at a low sintering temperature, as reported in this work, provides a reference for other advanced ferrites.

Crystallographically textured Ba0.8La0.2Fe11.8-xCu0.2O19-δ hexaferrites with narrow FMR linewidth

M-type hexaferrites which exhibit strong uniaxial anisotropy field, are promising for the applications in self-biased microwave and millimeter wave (MMW) devices. Here we demonstrate crystallographically textured hexaferrites with narrow ferromagnetic resonance (FMR) linewidth synthesized by the conventional ceramic method. Meanwhile, the relationship between iron-deficiency content and microstructure, crystallographic, and magnetic properties are researched. These hexaferrites have strong remanence ratio of above 0.9 along c-axis. By fitting of Lorentzian function to absorption derivative, we probe detailedly into the zero-field FMR linewidth of Ba0.8La0.2Fe11.8-xCu0.2O19-δ hexaferrites. When x equals 1.0, it indicates the narrowest FMR linewidth of 324Oe, as compared with previous reports for crystallographically textured hexaferrites.

Bi-YIG ferrimagnetic insulator nanometer films with large perpendicular magnetic anisotropy and narrow ferromagnetic resonance linewidth

Ferrimagnetic insulator Bismuth-substituted YIG (Bi1Y2IG) thin films with thickness from 8.2 nm to 31.7 nm and roughness smaller than 0.5 nm have been grown on substituted Gd3Ga5O12 (sGGG) substrate by pulsed laser deposition (PLD). A comprehensive description of the structural characteristics and magnetic properties of Bi-YIG films were given. Thickness-dependent large perpendicular magnetic anisotropy (PMA) was induced in Bi-YIG films by tensile strain originate from lattice mismatch. MOKE and VSM results showed that the 8.2 nm and 17.8 nm film has large PMA, high squareness and small out-of-plane coercivity with a saturation magnetization of 115 emu/cm3. However, with the increasing of film thickness, the easy axis turned from out-of-plane to in-plane. The thickness-dependent PMA indicated that the increase in PMA was caused by the interfacial strain. Furthermore, the Dzyaloshinskii–Moriya interaction (DMI), which is proportional to the strength of spin orbit coupling could also contribute to the increasing of PMA. First-principles calculations were adopted to study the elastic properties of Bi-YIG films. It showed that the Young’s modulus of Bi-YIG increased to 225 GPa, which giving a larger Kuλ than un-doped YIG films under same strain. The measured peak to peak linewidth ΔH of Bi-YIG film with PMA is 20 Oe for fields out-of-plane. The derived Gilbert damping constant is 7.03 × 10−4, indicating a low magnetic loss.

Magnetoelectric Interactions in Composites of Ferrite Films on Lattice-Matched Substrates and Ferroelectrics

The converse magnetoelectric effect (CME, $i.e.$ the magnetic response to a static electric field) in ferrite-ferroelectric composites is important for an innovative class of voltage-tunable, high-frequency magnetic devices. Technical challenges persist, though, due to weak CME coupling, large ferromagnetic-resonance (FMR) linewidth, and the need for a large bias magnetic field. This study aims to overcome those challenges by using single-crystal-like nickel ferrite films exhibiting high magnetostriction and narrow FMR linewidth. These films present a very high growth-induced magnetic anisotropy field that eliminates the need for a bias field, and facilitates device integration.

Soft Magnetism, Magnetostriction, and Microwave Properties of Fe-Ga-C Alloy Films

A systematic investigation of the soft magnetism, the change of modulus of elasticity with magnetization (ΔE effect), magnetostriction, and microwave properties has been carried out on iron-gallium-carbon thin films over a wide carbon content range. The phase transformation of the Fe-Ga-C films from bcc polycrystalline to amorphous leads to excellent magnetic softness with a low coercivity of less than 1 Oe, high saturation magnetization, narrow ferromagnetic resonance linewidth at 10 GHz of 20 to 30 Oe, and an ultra-low Gilbert damping constant of 0.0027. A record high piezomagnetic coefficient of 9.71 ppm/Oe, high saturation magnetostriction constant of 81.2 ppm, and large ΔE effect of -120 GPa at 500 nm were achieved.

Textured M-type barium hexaferrite Ba(ZnSn)xFe12−2xO19 with c-axis anisotropy and high squareness ratio

A series of oriented M-type barium hexaferrites (BaM) of composition Ba(ZnSn)xFe12−2×O19 (where x = 0, 0.2, 0.4, and 0.6) was fabricated. Pure BaM phase formation for all samples was confirmed by the X-ray diffraction patterns. The scanning electron microscopy images revealed that the grains in the oriented BaM had realigned along the hexagonal crystallographic c-axis, which was in good agreement with the results of magnetic hysteresis loops. Moreover, by treating under appropriate sintering conditions, oriented BaM with a high squareness ratio (Mr/Ms = 0.81) was obtained. Owing to the Zn–Sn substitution, the magnetocrystalline anisotropy field (Hk) decreased dramatically while maintaining the c-axis anisotropy, except for x = 0.6. A narrow ferromagnetic resonance linewidth ΔH of 667 Oe was measured when x = 0.4. The oriented BaM are potential candidates for the design of self-biased microwave devices such as circulators and isolators operated at low frequencies.

Voltage control of magnetism in NiZn ferrite/mica/PMNPT heterostructure with giant tunability and narrow linewidth

Recently, large magnetoelectric coupling of a spinel/piezoelectric heterostructure has been reported. However, the linewidth of the spinel is very large due to lattice mismatch when ferrite is directly deposited on piezoelectric substrates. This indicates a large magnetic loss, which impedes the spinel/piezoelectric heterostructure from useful device applications. Mica is a well-known 2D material, which can be split manually layer by layer without the substrate clamping effect. In this report, NiZn ferrite was deposited on a mica substrate by a spin-spray deposition technique. Spin-spray deposition is a wet chemical synthesis technique involving several chemical reactions for generating high-quality crystalline spinel ferrite films with various compositions directly from an aqueous solution. The thickness of ferrite is 2 μm, and the linewidth of the ferromagnetic resonance (FMR) is 115 Oe which is suitable for RF/microwave devices. The large FMR field tuning of 605 Oe was observed in NiZn ferrite/mica/PMN-PT heterostructures with minimal substrate clamping effect by reducing the thickness of the mica substrate. These multiferroic heterostructures exhibiting combined giant magnetoelectric coupling and narrow ferromagnetic resonance linewidth offer great opportunities for flexible RF magnetic devices.

Microstructure and microwave magnetic properties of Low-Firing Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ferrite

Low firing temperature and excellent gyromagnetic properties such as high remanence square ratio and narrow ferromagnetic resonance line width are required for the application in nonreciprocal microwave ferrite devices based on low temperature cofired ceramics (LTCC) technology. In this research, Bi2O3-Li2CO3 mixture was introduced as the sintering agent to lower the sintering temperature of Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ferrite. The influence of Bi2O3-Li2CO3 mixture upon the phase composition, composite microstructures and gyromagnetic properties of LiZnTiMn ferrite sintered at low temperature has been investigated for LTCC integration applications. With a proper amount of Bi2O3-Li2CO3 mixture, the sintering temperature of LiZnTiMn ferrite successfully reduced to below 900°C from 1100°C without degradation of magnetic properties, meanwhile, both of saturation flux density and remanence square ratio were increased.

Patterned growth of crystalline Y3Fe5O12 nanostructures with engineered magnetic shape anisotropy

We demonstrate patterned growth of epitaxial yttrium iron garnet (YIG) thin films using lithographically defined templates on gadolinium gallium garnet substrates. The fabricated YIG nanostructures yield the desired crystallographic orientation, excellent surface morphology, and narrow ferromagnetic resonance (FMR) linewidth (∼4 Oe). Shape-induced magnetic anisotropy is clearly observed in a patterned array of nanobars engineered to exhibit the larger coercivity (40 Oe) compared with that of continuous films. Both hysteresis loop and angle-dependent FMR spectra measurements indicate that the easy axis aligns along the longitudinal direction of the nanobars, with an effective anisotropy field of 195 Oe. Our work overcomes difficulties in patterning YIG thin films and provides an effective means to control their magnetic properties and magnetic bias conditions.