Barium hexagonal ferrites exhibiting unique self‐biasing characteristics have great potential for application in planar microwave devices, such as self‐biased circulators. Cu doping is an effective ...method to tailor their anisotropy field and ferrimagnetic resonance (FMR) linewidth to meet the requirements for low‐frequency low‐loss microwave devices. However, the regulation mechanism of Cu doping is still obscure, and its regulation effect is not optimized. Here, the magnetic and microwave properties of two groups of barium hexaferrites with site‐controlled Cu doping are reported. The diffusion dynamics of Cu2+ ions are comprehensively investigated, revealing significant differences in the concentration distribution and polycrystalline morphology, when comparing CuO as a reactant and sintering additive. The accumulation of Cu2+ ions at grain boundaries contributes to the increase in coercivity, whereas the dispersion of Cu2+ ions in crystallites leads to the decrease in the anisotropy field. Moreover, by introducing Cu2+ ions into the interstitial positions of the lattice, barium hexaferrites with a narrow FMR linewidth of 303 Oe and a high remanence ratio of 0.82 are achieved. These results represent the lowest FMR linewidth reported in polycrystalline hexagonal ferrites and prove the great technological value and commercial potential of Cu‐doped barium hexaferrites for next‐generation planar microwave devices.
Alkaline electrolyte based Zn batteries, relying on the redox reaction of Zn/ZnO (−1.35 V
vs.
SHE), offer a higher output voltage compared with neutral or mild electrolyte based Zn batteries (redox ...reaction of Zn/Zn
2+
, −0.76 V
vs.
SHE). However, the dendrite issue in alkaline electrolytes is also much exaggerated and leads to poor reversibility. To tackle the severe dendrite issue in alkaline electrolytes, a static magnetic field is introduced in this work to regulate the Zn deposition/dissolution behavior. A uniform Zn plating layer is obtained and validated by
in situ
optical microscopy. Surface roughness with a magnetic field (0.74 μm) is significantly reduced compared to that without a magnetic field (61.46 μm). COMSOL numerical simulation and electrochemical tests reveal that zincate ions can be subjected to the Lorentz force under a magnetic field, giving rise to micro-rotation and the magnetohydrodynamic (MHD) effect, which greatly alleviates the concentration polarization and enhances the mass transfer. Accordingly, the Zn symmetrical battery with alkaline electrolytes under a magnetic field can sustain up to a long cycle life of 260 h at 1 mA cm
−2
. Moreover, a Zn-air full battery with a magnetic field can keep working stably for 200 h at a high current density of 10 mA cm
−2
. The application of an external magnetic field in alkaline Zn batteries provides a practical and effective solution for addressing the Zn dendrite issue in alkaline electrolytes.
A novel strategy of applying external magnetic fields is proposed to tackle the challenging alkaline Zn dendrite issue. Benefiting from the magnetohydrodynamic effect, the ultra-flat zinc deposit and long-term cycling stability of the Zn battery was achieved.
FM (ferromagnetic)/AF (antiferromagnetic) heterogeneous multilayer films, with high-saturation magnetization (4π
M
s
), low coercivity (
H
c
), and low ferromagnetic resonance (FMR) linewidth (∆
H
), ...have great application prospects in microwave/millimeter-wave devices. In this study, the Ni
81
Fe
19
(
t
nm)/Fe
50
Mn
50
(15 nm)/Ni
81
Fe
19
(
t
nm) films were fabricated by DC magnetron sputtering, and the effects of thickness of the Ni
81
Fe
19
on the microstructure, static magnetic properties and microwave properties were investigated. With the increasing thickness of Ni
81
Fe
19
film, the saturation magnetization increased from 658 to 754 emu/m
3
. The in-plane and out-of-plane coercivity both decreased first and then increased, and ∆
H
decreased first and then raised from 193 to 95 Oe. When the thickness of the Ni–Fe film is 50 nm, the transition of the out-of-plane exchange bias field from the negative exchange bias to the positive exchange bias occurred. Remarkably, with a 50 nm Ni
81
Fe
19
film, the multilayer films achieved excellent performance with high-saturation magnetization (4π
M
s
, 722 emu/m
3
), low in-plane coercivity (
H
c
, 0.61 Oe), and low FMR linewidth (∆
H
, 95 Oe). The outstanding heterogeneous multilayer films exhibit great potentials in microwave/millimeter-wave devices.
As the macro behavior of the strength of exchange interaction, state of the art of Curie temperature T
, which is directly proportional to the exchange integrals, makes sense to the high-frequency ...and high-reliability microwave devices. Challenge remains as finding a quantitative way to reveal the relationship between the Curie temperature and the exchange integrals for doped barium hexaferrites. Here in this report, for La-substituted barium hexaferrites, the electronic structure has been determined by the density functional theory (DFT) and generalized gradient approximation (GGA). By means of the comparison between the ground and relative state, thirteen exchange integrals have been calculated as a function of the effective value U
. Furthermore, based on the Heisenberg model, the molecular field approximation (MFA) and random phase approximation (RPA), which provide an upper and lower bound of the Curie temperature T
, have been adopted to deduce the Curie temperature T
. In addition, the Curie temperature T
derived from the MFA are coincided well with the experimental data. Finally, the strength of superexchange interaction mainly depends on 2b-4f
, 4f
-12k, 2a-4f
, and 4f
-12k interactions.
Manganese-zinc (MnZn) ferrites have important application in convertors and switching mode power supplies. The core losses (<inline-formula> <tex-math notation="LaTeX">\text{P}_{L} ...</tex-math></inline-formula>) of MnZn ferrites have serious influence on the performance of power conversion devices. It is worth emphasizing that reducing the core losses at high frequency is of great significance for the miniaturization and integration of power conversion devices. Here in this paper, MnZn ferrites have been fabricated by the method of solid-state reaction, and the effect of CaCO 3 and V 2 O 5 co-additives on the microstructure and magnetic property has been investigated. This paper illustrated the competition mechanism of grain growth, which originated from the hindrance effect of CaCO 3 and acceleration effect of V 2 O 5 , as well as the effect of CaCO 3 and V 2 O 5 on core losses by means of loss separation method. In addition, as for the MnZn ferrite sample with 0.1 wt% CaCO 3 and 0.01 wt% V 2 O 5 co-additives, core losses were suppressed to 46 and 664 kW/m 3 corresponding to 3 MHz 10 mT and 3 MHz 30 mT at 25 °C, respectively. The state-of-the-art MnZn ferrites with ultralow core losses own potential application for high-frequency power conversion devices.
•The first order crystalline constants were calculated for LiZnMn ferrite.•The FMR linewidth had been separated based on spin-wave approach at X-band.•The mechanism of dielectric polarization and ...dielectric loss were studied at X-band.
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).
Ferrites which have relatively high remanence ratio, large coercivity and strong anisotropy are needed to meet the increasing demand for devices used in millimeter-wave frequency. Herein, we ...demonstrate a composition of Sr
0.7
La
0.3
Fe
12−
x
Al
x
O
19
hexaferrites prepared by the conventional ceramic method. We investigate the phase, morphology and magnetic properties of Al-substituted strontium hexaferrites. This study illustrates that aluminum substitution has a significant effect to improve the coercivity and anisotropic field. Finally, we propose an empirical relationship between the functional properties of Al-substituted ferrites and the amount of aluminum.
To ensure that the performance of filters matches the continuous development in communication frequency bands, the influence of temperature on filter performance must be considered during the ...fabrication of filters. In this study, a cavity-type temperature-compensated film bulk acoustic resonator (TC-FBAR) device was prepared with an SiO2 temperature filter between the bottom electrode and the piezoelectric layer. A one-dimensional Mason model of the TC-FBAR was established. An advanced design system, a high-frequency structure simulator, and COMSOL software were used to optimize the design of the TC-FBAR. After the optimization, the out-of-band rejection was improved by 10 dB. To address the compensation effect of the tensile and compressive stresses, a multilayer film was implemented for low-stress control and a reduction in stress to |P| ≤ 150 MPa, thereby improving the orientation of the piezoelectric film. Moreover, the influence of the thickness of the SiO2 temperature-compensated layers on the temperature-compensated characteristics was studied. When the SiO2 thickness was 50 nm, the temperature coefficient of frequency (TCF) was ±1 ppm/°C. The center frequency and 3 dB bandwidth of TC-FBAR were 2.492 GHz and 15.02 MHz, respectively, and the center insertion loss was −3.1 dB. Moreover, the out-of-band rejection was greater than 40 dBc, and TCF was 0.8 ppm/°C.
In response to the demands for high frequency, miniaturization, and high integration in electronic devices, such as inductors and DC-DC convertors, nickel–zinc ferrite thin films exhibit significant ...application value and development potential. For regulating the magnetic properties and microstructure of spin-sprayed polycrystalline ferrite materials, a comprehensive understanding of the impact of oxidant concentration on film reaction is essential. This study finds that as the concentration of the NaNO2 oxidant increases, the grain size of the nickel–zinc ferrite thin film samples progressively enlarges. Due to the preferential occupation of iron ions at the B sites, the saturation magnetization correspondingly increases. However, when the oxidant concentration becomes excessive, the preferential (222) orientation growth of the film is disrupted, leading to the agglomeration and uneven growth of grains, transitioning from triangular plate-like to spherical in shape. This increase in grain size alters the magnetization mechanism of the thin film, predominantly favoring domain wall movement. Upon analyzing the microstructure and magnetic characteristics, it becomes evident that the concentration of oxidant is a key determinant in the spin-spray deposition process.
In certain applications, such as on-chip integrated inductors, ferrite materials are highly desirable owing to their superior magnetic and insulation properties. Spin-spray deposition is a promising ...method for producing high-quality thin films of ferrite, as it does not require a vacuum and can operate at low temperatures. A comprehensive analysis was conducted to investigate the influence of the substrate on the microstructure and magnetic properties of the thin films, and the growth mechanism of this phenomenon was discussed. In addition, first-order reversal curve measurements were used to study the coercivity and grain size distribution. The results indicate that thermal conductivity played a significant role in determining the thin-film growth during spin spray deposition. Polyimide is considered a more suitable substrate under this process due to its appropriate thermal conductivity, which results in more uniform grain distribution and improved magnetic properties, with maximum permeability and a cutoff frequency reaching 55 and 485 MHz, respectively. Our results provide valuable insights into the mechanism of spin-spray deposition and offer an effective way to tune the performance of ferrite thin-film materials.
PDF
