Low Ferromagnetic Resonance Linewidth Research Articles

Target grain size dependence of the morphology, crystallinity and magnetic properties of yttrium iron garnet films

In this work, yttrium iron garnet films were prepared on a Ga3Gd5O12 substrate by pulsed laser deposition. The dependence of target grain size on the morphology, crystallinity, and magnetism of films was investigated. Firstly, X-ray diffraction revealed that the fine grain size of the target was beneficial for increasing the crystallinity of films. Secondly, scanning electron microscopy and roughness measurements displayed the film prepared by the small grain size of the target has better morphology and lower roughness. Lastly, magnetic hysteresis loops and ferromagnetic resonance measurements further shown that a good microstructure and fine grain size of target facilitated the growth of film with greater magnetic properties. Consequently, YIG film deposited by 1.0 μm-target has magnetic properties with a high saturation magnetization of 155 emu/cm3, a low saturation magnetic field of 1077 Oe, and low ferromagnetic resonance linewidth of 42 Oe.

Nano-TiO2 substituted LiZnBi ferrite ceramics with low sintering temperature and enhanced magnetic properties for LTCC applications

Saturation magnetization (4πMs) and ferromagnetic resonance linewidth (ΔH) are vital parameters for microwave devices application. The material with high 4πMs and low ΔH is available in microwave frequency. In this work, to synthesize a ferrite material applied to X band, high saturation magnetization LiZnBi ferrite ceramics were selected as matrix. Further, in order to reduce magnetic loss of the LiZnBi ferrites sintered at low temperatures, various nano-TiO2 were added. Interestingly, the nano-TiO2 can promote grains growth and suitably enhance saturation magnetization and lower coercivity at low sintering temperature. Meanwhile, the ferromagnetic resonance linewidth (ΔH) of the ferrites can also be reduced by introducing more nano-TiO2 particles. At last, a nano-TiO2 substituted LiZnBi ferrite ceramics (x = 0.25) with high saturation magnetization (4πMs = ∼3367 G), low coercivity (Hc = ∼146.2 A/m) and low ferromagnetic resonance linewidth (ΔH = ∼192 Oe) were obtained at 880 °C. The ferrite material is serviceable for X band microwave devices, such as phase shifter and circulator.

Enhanced gyromagnetic properties of NiCuZn ferrite ceramics for LTCC applications by adjusting MnO2-Bi2O3 substitution

The demand for high performance microwave devices is increasingly promoting the development of miniaturization, integration and multifunctionalization. Here, a uniform and dense NiCuZn ferrite ceramic with high saturation magnetization and low ferromagnetic resonance linewidth was obtained at 950 °C by adjusting the MnO2-Bi2O3 composite additives. The MnO2-Bi2O3 composite additives were composed of 0.5 wt% MnO2 and x wt% Bi2O3 (x = 0.0, 0.5, 1.0, 1.5, 2.0, and 3.0). The phase structure, microstructures and magnetic properties were systematically studied by means of modern measurement techniques. SEM images reveal that appropriate MnO2-Bi2O3 additions can promote grain growth and reduce sintering temperatures, which is very advantageous for LTCC technology. In addition, the content of MnO2-Bi2O3 additives can significantly reduce ferromagnetic resonance linewidth (FMR) by promoting grain growth and densification at low temperatures. Finally, a uniform and compact NiCuZn ferrite ceramic with an improved 4πMs (~ 3812.5 Gauss), a narrow ΔH (~ 144.6 Oe), and a reduced Hc (~ 85.2 A/m) were obtained (at 950 °C) by adding the optimal volume of Bi2O3 additive. It is expected that the improved gyromagnetic performances will allow the NiCuZn ferrite ceramics to be promising candidates for X-band microwave devices.

Controlling the magnetic anisotropy in epitaxial Y3Fe5O12 films by manganese doping

Controlling the magnetic anisotropy in epitaxial ${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$ (YIG) thin films is critical for magnonic and photonic device applications. In this paper, we report the crystal structure, magnetic properties, and magnetic anisotropy of epitaxial ${\mathrm{Y}}_{3}(\mathrm{F}{\mathrm{e}}_{5\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}){\mathrm{O}}_{12}$ (Mn:YIG) thin films grown on $\mathrm{G}{\mathrm{d}}_{3}\mathrm{G}{\mathrm{a}}_{5}{\mathrm{O}}_{12}$ (111) (GGG) substrates by pulsed-laser deposition. Mn doping is observed to strongly enhance the magnetoelastic coefficient of YIG thin films, which leads to large tunability of the thin film magnetic anisotropy by lattice strain. With increasing Mn concentration from $x=0$ to $x=1.25$, a continuous increase of out-of-plane magnetic anisotropy ranging from \ensuremath{-}644.4 Oe to 1337.5 Oe is observed. In particular, a perpendicular magnetic anisotropy (PMA) is achieved in Mn:YIG thin films with a high Mn concentration of $x=1.12$. Ferromagnetic resonance (FMR) measurements show low FMR linewidths of 3.4 Oe to 129 Oe at 9.5 GHz in Mn:YIG thin films. Our paper demonstrates manganese doping as an effective way to enhance the magnetoelastic anisotropy of YIG thin films by strain, which is useful for magnonic and magneto-optical device applications.

Synthesis of Highly Uniform and Compact Lithium Zinc Ferrite Ceramics via an Efficient Low Temperature Approach.

LiZn ferrite ceramics with high saturation magnetization (4πMs) and low ferromagnetic resonance line widths (ΔH) represent a very critical class of material for microwave ferrite devices. Many existing approaches emphasize promotion of the grain growth (average size is 10-50 μm) of ferrite ceramics to improve the gyromagnetic properties at relatively low sintering temperatures. This paper describes a new strategy for obtaining uniform and compact LiZn ferrite ceramics (average grains size is ∼2 μm) with enhanced magnetic performance by suppressing grain growth in great detail. The LiZn ferrites with a formula of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 were prepared by solid reaction routes with two new sintering strategies. Interestingly, results show that uniform, compact, and pure spinel ferrite ceramics were synthesized at a low temperature (∼850 °C) without obvious grain growth. We also find that a fast second sintering treatment (FSST) can further improve their gyromagnetic properties, such as higher 4πMs and lower ΔH. The two new strategies are facile and efficient for densification of LiZn ferrite ceramics via suppressing grain growth at low temperatures. The sintering strategy reported in this study also provides a referential experience for other ceramics, such as soft magnetism ferrite ceramics or dielectric ceramics.

Polycrystalline Bi substituted YIG ferrite processed via low temperature sintering

Polycrystalline Bi substituted YIG ferrite (i.e., Y3-xBixFe5O12) has been widely studied due to its high electrical resistivity, moderate to high magnetization and permeability, and relatively low processing cost. Furthermore, it is suitable for large-scale industrial production making it a viable material for mass-produced filters, inductors, isolators, and other rf components. However, low temperature co-fired ceramic technology requires sintering temperatures below ∼960 °C (i.e., the approximate melting point of the silver electrodes are ∼961 °C) while maintaining a low ferromagnetic resonance linewidth (ΔH) and other desirable properties. This work reports the effect of bismuth addition on the ferromagnetic properties of low-temperature sintered Y3-xBixFe5O12 (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2) garnet ferrites. The microstructure, magnetic properties, and gyromagnetic properties of the Bi-YIG samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and ferromagnetic resonance (FMR). Results support the processing of pure phase garnet, with moderate values of saturation magnetization and FMR linewidth for x = 0.9. Moreover, the Fano algorithm was shown to provide superior fitting to asymmetric FMR spectra allowing for very accurate measurement of ΔH.

Magnetic properties and microstructure of low temperature sintered LiZnMnTi ferrites doped with Li2CO3[sbnd]B2O3[sbnd]Bi2O3[sbnd]SiO2 glasses

LiZnMnTi ferrite, composed of Li0.35Zn0.3Mn0.05Ti0.1Fe2.07O4, possesses superior magnetic properties when sintered at high temperature. To obtain great performance at low sintering temperature (below the melting point of Ag), Li2CO3B2O3Bi2O3SiO2 (LBBS) glasses was introduced into the LiZnMnTi ferrites. Results show that the LBBS glass makes great contributions to achieve low temperature sintering (∼920 °C) and the ferrites keep superior magnetic properties. On the one hand, the additive of LBBS glass (0.50 wt%) can largely improve saturation induction (∼330 mT), remanence square ratio (∼0.83) and lower coercive force (∼180 A/m). Meanwhile, a low ferromagnetic resonance line width (∼240 Oe) at 9.3 GHz was obtained. A higher saturation magnetization (∼56 emu/g) was also attained when amount of the glass additive is around 0.50 wt%. The results indicate that the LBBS glass is a good sintering aid for lowering the firing temperature of LiZnMnTi ferrites for microwave device applications.

Effect of ZnO–B2O3–SiO2 glass additive on magnetic properties of low-sintering Li0.43Zn0.27Ti0.13Fe2.17O4 ferrites

ZBS glasses (0.125–2.0 wt%) composed of ZnO–B2O3–SiO2 were added into the LiZnTi (Li0.43Zn0.27Ti0.13Fe2.17O4) ferrites to achieve low temperature sintering. Variations in microstructure, bulk density and ferromagnetic properties of the ferrites along with the changes of ZBS glasses concentration were discussed and analyzed in detail. Results suggest that LiZnTi ferrites mixed with appropriate amount of ZBS glass possess high saturation magnetization intensity, low coercivity, and low ferromagnetic resonance line width. Although this sintering process was completed at a low temperature (~900 °C), the ferrites still kept relatively good magnetic properties. Thus, the ZBS glass is a promising additive for low temperature sintering of LiZnTi ferrites.

Effect of NiZn Ferrite Nanoparticles upon the Structure and Magnetic and Gyromagnetic Properties of Low-Temperature Processed LiZnTi Ferrites

NiZn ferrite nanoparticles (2–20 wt %) of composition Ni0.4Zn0.6Fe2O4 were introduced into LiZnTi ferrite of composition Li0.42Zn0.27Ti0.11Fe2.2O4 and sintered at a temperature of 920 °C for 2 h, well below that of the Ag melting point. Here, LiZnTi ferrites were prepared by a solid-state reaction method, and NiZn ferrite nanoparticles were fabricated by a hydrothermal chemical technique at 180 °C. A low ferromagnetic resonance (FMR) line width, low coercivity, and high magnetic moment were achieved after refinement of the heat treatment conditions of the mixture. Riveted full profile refinement of the X-ray powder diffraction patterns and analysis of Mossbauer spectra were employed to study the structure and caption distribution. The results confirm a pure spinel phase after processing. A narrow FMR line width of 152.5 Oe, a reduced coercivity of 132.9 A/m, and an improved saturation magnetization of 74.23 emu/g were obtained by way of the addition of 8 wt % NiZn ferrite nanoparticles.

Preparation of low ferromagnetic resonance linewidth yttrium iron garnet films on silicon substrate

Abstract Yttrium iron garnet films were prepared on silicon substrate by pulsed laser deposition. Compositional buffer layers composed by CeO2/YSZ (YSZ: yttria-stabilized ZrO2) and multi-low temperature buffer layers (Y3Al5O12, Y3Al2.5Fe2.5O12, Y3Fe5O12) (shortened form as CeO2/YSZ and multi-LT buffer layer) were employed to achieve low ferromagnetic resonance width. The effects of buffer layers on the microstructures, crystallinity and low ferromagnetic resonance linewidth of films were studied. A FMR linewidth of 53 Oe were obtained, which was ascribed to its well crystallinity, high dense and uniform grain size.

Self-assembled 1-3D Pb(ZrTi)O3-NiFe2O4 magnetoelectric nanocomposite films with narrow FMR linewidth

Ferrites are critical for nonreciprocal RF/microwave devices. In the current work, epitaxial NiFe2O4 nanowires were self-assembled in Pb(ZrTi)O3 matrix on a (001)-oriented MgAl2O4 single-crystal substrate by a 90° off-axis RF magnetron sputtering method. The influences of substrate temperature, argon-over-oxygen ratio and RF power on the growth of NiFe2O4 nanowires have been addressed. Owing to the excellent lattice match between the NFO phase and the PZT matrix, very low ferromagnetic resonance (FMR) linewidth of 139 Oe was obtained at 8.969 GHz, even better than the single-layer epitaxial NiFe2O4 film, therefore making them suitable for RF/microwave nonreciprocal devices.

Magnetic and microwave properties of U-type hexaferrite films with high remanence and low ferromagnetic resonance linewidth

U-type barium hexaferrite films (Ba4Ni1.4Co0.6Fe36O60) were deposited on (0001) sapphire substrates by pulsed laser deposition. Microstructure and magnetic properties of the films were characterized by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. Ferromagnetic resonance (FMR) measurements were performed at X-band. The results indicate an anisotropy field of ∼8 kOe, and the saturation magnetization (4πMs) of ∼3.6 kG. An optimal post-deposition annealing of films results in a strong (0 0 n) crystallographic texture and a high hysteresis loop squareness (Mr/Ms = 92%) leading to self biased properties. Furthermore, the highly self-biased ferrite films exhibited an FMR linewidth of ∼200 Oe. The U-type hexaferrite films having low microwave loss, low magnetic anisotropy field, and high squareness are a suitable alternative to Sc or In doped BaM ferrites that have been the choice material for self-biased microwave devices at X-band frequencies.

Effects of Bi2O3 on FMR linewidth and microwave dielectric properties of LiZnMn ferrite

Effects of Bi2O3 on ferromagnetic resonance (FMR) linewidth and microwave dielectric properties for LiZnMn ferrite prepared by a conventional ceramic method were investigated. The FMR linewidth had been separated to anisotropy and porosity line broadening contributions by an approximate calculation based on spin-wave approach. The results manifest that, Bi2O3 content significantly affects FMR linewidth via promoting grain growth and densification. With Bi2O3 concentration increasing, anisotropy contribution is changeless with a constant about 80Oe. The variation of the porosity line broadening contribution, however, is unanimous with the FMR linewidth. Meanwhile, the mechanism of dielectric polarization and dielectric loss of the samples were discussed. When the amount of Bi2O3 is 1.00wt%, the sample shows low FMR linewidth (ΔH, 133Oe) and low dielectric loss tangent (tan δε, 5×10−4) at 9.2GHz, high saturation magnetization (Ms, 415kA/m), and high squareness ratio (Br/Bs, 0.87).

RF Magnetic Properties of FeCoB/Al$_{2}$O$_{3}$/FeCoB Structure With Varied Al$_{2}$O$_{3}$ Thickness

Physical vapor deposition prepared FeCoB(100 nm)/Al2O3/FeCoB(100 nm) sandwich structures with different Al2O3 thickness (2 to 15 nm) were studied. The magnetization curves showed that the in-plane coercive field and saturation field along the easy axis decreased with increase in Al2O3 thickness. The saturation magnetization field 4 πMs for all samples is above 1.6 T. The coercive field remained below 0.5 Oe for Al2O3 thickness greater than 6 nm, approximately when the antiferromagnetic coupling switched to ferromagnetic coupling. The existence of optical modes in ferromagnetic resonance (FMR) curves confirmed antiferromagnetic coupling in samples with Al2O3 thickness below 6 nm. At 8.5 GHz, the sandwich structure with a 3 nm Al2O3 layer displayed a narrow linewidth of only 29 Oe, indicating lower magnetic loss in the sandwich structure compared to the single layer FeCoB with a thickness of 200 nm that exhibited a linewidth of 50 Oe. Also, all sandwich structures demonstrated real relative permeability of above 600 up to 1.5 GHz. The FeCoB(100 nm)/Al2O3 (3 nm)/FeCoB(100 nm) structure with low coercive field, high magnetization, and low FMR linewidth presents great potential in RF magnetic application.

Perpendicularly Oriented Polycrystalline BaFe11.1Sc0.9O19 Hexaferrite with Narrow FMR Linewidths

We demonstrate low ferromagnetic resonance (FMR) linewidths and high remanence magnetization in polycrystalline M‐type Sc‐doped Ba ferrites having anisotropy fields of ∼8 kOe and perpendicular orientation of the spontaneous magnetization vector. This is a result of applying a unique processing technique that makes use of a polymer network‐assisted alignment of hexaferrite particles in high magnetic fields. The resulting compacts exhibit high squareness (Mr/Ms∼92%) and low FMR linewidths (∼530 Oe) at X‐band and Ka‐band. This represents an ∼74% decrease in linewidth compared with previous reports for polycrystalline BaM ferrites using conventional processes. We also have detailed origins of the FMR linewidth broadenings in terms of some important theoretical models. These materials have potential for use in low frequency self‐biased microwave/millimeter devices such as circulators and isolators.

Epitaxial growth of M-type Ba-hexaferrite films on MgO (111)‖SiC (0001) with low ferromagnetic resonance linewidths

Barium hexaferrite (BaM) films were deposited on 10nm MgO (111) films on 6H silicon carbide (0001) substrates by pulsed laser deposition from a homogeneous BaFe12O19 target. The MgO layer, deposited by molecular beam epitaxy, alleviated lattice mismatch and interdiffusion between film and substrate. X-ray diffraction showed strong crystallographic alignment while pole figures exhibited reflections consistent with epitaxial growth. After optimized annealing, these BaM films have a perpendicular magnetic anisotropy field of 16900Oe, a magnetization (as 4πMs) of 4.4kG, and a ferromagnetic resonance peak-to-peak derivative linewidth at 53GHz of 96Oe, thus demonstrating sufficient properties for microwave device applications.

Multifunctional dual-tunable low loss ferrite-ferroelctric heterostructures for microwave devices

Oriented barium ferrite (BaM) and polycrystalline ferroelectric barium strontium titanate (BSTO) layered structures have been fabricated by pulsed laser deposition. The 0.5μm thick BaM layer has a saturation induction of 4kG, a uniaxial effective anisotropy field of 16kOe, and a relatively low ferromagnetic resonance linewidth of about 25Oe, values that are indicative of a high quality film. The dielectric constant of the 0.9μm thick BSTO layer drops by a factor of 2 for an applied voltage of 3V.

Screen printed thick self-biased, low-loss, barium hexaferrite films by hot-press sintering

Ba Fe 12 O 19 hexaferrite thick films having high hysteresis loop squareness (Mr∕Ms) and low ferromagnetic resonance (FMR) linewidths were processed through the use of a screen printing technique coupled with hot-press sintering. Scanning electron microscopy and x-ray diffraction measurements exhibit strong crystallographic c-axis alignment of crystals perpendicular to the film plane. Static magnetic resonance and FMR measurements were performed to determine the effect of the preparation technique on magnetic hysteresis and microwave properties. Hot pressing during sintering produced dense thick films having high squareness (>0.95) and reduced coercivity (∼1900Oe). Of greater importance was the measurement of a minimum peak-to-peak FMR linewidth, 320Oe at the U band, for films ranging in thickness from 100to500μm. Theoretic estimates suggest that such narrow linewidths can be attributed to the reduction in porosity and the improvement in c-axis orientation of crystallites in polycrystalline barium ferrite films. As such, haxaferrite materials prepared using this technique offer opportunities in the next generation of self-biased planar microwave devices.

Spin–wave instability measurements in Mn substituted single-crystal Zn2Y hexagonal ferrite thin disks at 8.9 GHz (abstract)

Large magnetocrystalline anisotropy makes hexagonal ferrites attractive for microwave and millimeter wave applications. Critical to such applications is the response at high power levels. Relatively little work has been reported in this area. In order to characterize this response, the minimum microwave field amplitude required to excite spin–wave instability, hcrit, is measured for various field–sample configurations. Plots of hcrit versus static field H, termed “butterfly” curves, are then used to obtain spin wave linewidths and define operational power limits for device applications. Two regimes were studied in this work: (1) saturation of the ferromagnetic resonance (FMR) absorption; and (2) parallel pumping instability for fields well below FMR. The objective was to measure butterfly curves and use the results to determine values of the spin–wave linewidth ΔHk. The measurements were made on a 1.2 mm diam 0.15 mm thick single-crystal Mn substituted Zn2Y (Y-type) hexagonal ferrite c-plane (001) disk with easy plane anisotropy. The static field and the 4 μs wide, 30 Hz pulsed microwave field at 8.9 GHz were applied in the plane of the disk. Standard cavity techniques were used. The low power ferromagnetic resonance (FMR) linewidth was 15 Oe. For resonance saturation, the measured hcrit was 0.29 Oe at the FMR field of 775 Oe. The resonance saturation butterfly curve was asymmetric about its minimum value at FMR. The hcrit for parallel pumping was approximately 5 Oe and independent of H over the range of 150–350 Oe. These data and spin–wave instability theory were used to estimate ΔHk values. For parallel pumping, ΔHk was determined to be 17 Oe for the critical modes at one half the 8.9 GHz pump frequency. For resonant saturation, ΔHk was determined to be 12 Oe for the critical modes at the pump frequency.

Experimental conditions for magnetostatic wave envelope solitons

Yttrium iron garnet (YIG) films are widely used to study microwave excitations owing to their low ferromagnetic resonance linewidth. This property does not necessarily imply that the magnetostatic wave (MSW) solitons can propagate on the YIG films almost free of propagation losses. The nonlinear Schrodinger equation (NLSE) with the third order dispersion and dissipative effects has been used to describe magnetostatic forward volume wave envelope solitons. The split-step Fourier method has been used to solve the NLSE with the third order dispersion and dissipative effects. The numerical results show that the linewidth is not narrow enough to support the propagation of the magnetostatic wave (MSW) solitons. In order to observe a soliton-like behaviour in experiments, we must make the dispersion of the MSW so high that the waveform of an input pulse may make a sufficiently rapid change and the MSW soliton formation may be completed before the dissipative effect becomes prevailing.