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Acoustically actuated magnetoelectric (ME) antennas based on resonant magnetoelectric coupling within ferromagnetic/piezoelectric ME laminated composites have recently been considered as a promising solution for antenna miniaturization. However, its radiation performance has been theoretically overestimated, since the negative effects on performances due to the magnetization saturation and the nonlinear mechanical behavior that occur from high-field driving have not been paid enough attention. This work presents a unique equivalent-circuit-based numerical method to analyze the near-field resonance radiation performances of ME antennas driven by high electric fields. In this method, we establish an equivalent circuit of the converse magnetoelectric effect for a ME laminated composite to describe the operating principle of acoustically actuated electromagnetic radiation. The equivalent parameters related to resonance characteristics are determined by fitting the circuit model to the data from frequency response measurements of the near-field magnetic flux density. The validity of the model is verified by comparing the theoretical predictions with the experimental results, in the view of the volume fraction dependence of the mechanical resonance-related radiation characteristics of the fabricated ME composites. Based on the proposed model, the influence of driving voltage amplitude on near-field radiation performances is further analyzed by experimental fitting to the model, and the potential limiting factors of ME antennas are discussed according to the driving-amplitude dependence of parameters obtained from the fit. This work provides an effective and engineering-friendly approach to predict the evolution of ME antenna performances, leading a way to improve the performance limit for resonant magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

The micro-discharge effect limits the development of high-frequency microwave power components to miniaturization and integration. Therefore, it has become a focus of research to effectively suppress the micro-discharge effect, increase the micro-discharge threshold, and strengthen the environmental stability of high-frequency microwave devices. In this study, different elemental ratios of carbon (C)/silver (Ag)/titanium (Ti) composite films were obtained by multi-target magnetron co-sputtering technology and then systematically analyzed for micro-discharge effects. When the doping ratio of C/Ag/Ti was 3.538/1/0.013, the corresponding maximum secondary electron emission coefficient (δmax) decreased to 1.01 owing to the suppression of secondary electron emission by the increase in the content of sp2 hybrid bond. The micro-discharge threshold of Ku band waveguide filters coated with moderate C/Ag/Ti composite films showed an optimal performance of 10 000−12 500 W, which was increased by approximately 20 times. Moreover, the microstructure of the composite films exhibited higher density and flatness with a tiny increase in the titanium doping ratio, representing good environmental stability. Thus, the effective suppression of the secondary electron emission yield, significant improvement in the micro-discharge threshold, and enhancement of the environment stability of microwave components could be realized simultaneously by reasonably controlling the content of titanium in silver and titanium co-doped carbon-based composite films. [ABSTRACT FROM AUTHOR]

Half-metallic NiCo2O4 with high spin polarizability has great potential applications in spintronics. The manipulation of magnetic anisotropy is crucial for spintronics based on spin-transfer or spin–orbit torques, as it is directly related to the critical switching current density. Here, we report epitaxial growth of metallic NiCo2O4 film with perpendicular magnetic anisotropy on MgAl2O4 single crystal substrates. The modulation of the magnetic anisotropy was achieved by changing the growth conditions (deposition temperature and thickness) of NiCo2O4 films and by means of protonation. Strong dependence of magnetic coercivity on deposition temperature (350–500 °C) has been observed due to variable phase configuration. Furthermore, the magnetic coercive field can also be effectively controlled by the film thickness (3–78 nm) through strain relaxation. More importantly, spin reorientation transition has been achieved by proton and electron doping in the NiCo2O4 films, resulting in reconfigured valence states of Ni and Co cations and a magnetic easy axis rotation from out-of-plane to in-plane. The effective modulation of the magnetic anisotropy provides important insights into the functional design of NiCo2O4-based spintronics with ultralow energy dissipation. [ABSTRACT FROM AUTHOR]

The micro-discharge effect is a failure mechanism that often appeared in space microwave devices under vacuum conditions, such as RF (radio frequency) cavity, RF satellite missile, and antenna launching communication system. How to control micro-discharge effectively and simply has become a research hotspot. In this paper, we have prepared a series of doping silver (Ag)/carbon (C) composite films by double target magnetron sputtering technology and have significantly reduced the maximum secondary electron emission coefficient (δmax) from 2.522 to 1.04 when the doping ratio of Ag/C is 1.345. Theoretically, the continuous increase of sp2 hybrid bond content tuned by the existing Ag nanoparticles has a greater contribution to the conductivity and inhibition of secondary electron emission in the Ag/C composite films. Meanwhile, the gradually emerged "multi-trap" surface structure with the increase of Ag doping content has further increased the collision between excited secondary electrons and free electrons, achieving an obvious inhibition effect. The results demonstrate that secondary electron emission can be suppressed effectively by tuning the structural feature of two kinds of compounded materials with low δmax. It is of great significance in physical mechanism analysis and design of the new doping process. [ABSTRACT FROM AUTHOR]

The domain structure fundamentally determines the piezoelectric/ferroelectric performance of ferroelectric materials. To understand the correlation between macro-properties and microstructure, the evolution of domain structure should be clearly figured out. Here, the diffraction-plane-transformation (DPT) model is proposed for the domain evaluation in BS-PT piezoelectric ceramics of rhombohedral crystalline structure. The transformation between different crystal planes is accurately revealed by the DPT model. Then, non-180° domain reversal in rhombohedral 0.4BiScO3–0.6PbTiO3 piezoelectric ceramics (abbreviated as BS-PT) can be quantitatively estimated, whether in electric poling or thermal depoling processes. Experimentally, the correlations between piezoelectric coefficients, electromechanical coupling properties, and non-180° domain reversal percentage are investigated. It is proven that the DPT model provides an effective method for the non-180° domain estimation in rhombohedral crystalline ceramics. [ABSTRACT FROM AUTHOR]

The emerging market of wearable devices for tracking and positioning requires the development of highly flexible magnetic sensors. Due to the stable magnetoresistance ratio and simple fabrication process, sensors based on the anisotropic magnetoresistance (AMR) effect have been proposed as promising candidates. However, the stability of AMR sensors under different bending situations has rarely been investigated. In this work, we proposed a flexible AMR magnetic sensor deposited on an ultra-thin Kapton substrate, which exhibits excellent anti-fatigue behavior at different bending curvatures ranging from 1/3 to 1/10 mm−1. Experimental results show that the sensitivity of our proposed flexible AMR sensor remains as high as 0.25 Oe−1 after being bent 500 times, showing promising potential for application in wearable electronic devices. [ABSTRACT FROM AUTHOR]

Wireless strain sensors have received extensive attention owing to their wide application prospects in structural health monitoring, industrial automation, human activity monitoring, and intelligent robotic systems. Here, a wireless strain sensor prototype based on the magnetoelectric heterostructure of ferromagnetic thin films on a piezoelectric substrate has been developed. The ferromagnetic resonance (FMR) frequency of the sensor is strongly dependent on external strain due to the large magnetostriction of the film. The piezoelectric substrate with a programmable voltage has been used as a strain source for the characterization of the wireless strain sensor. The limit of detection of the wireless strain sensor is 0.54 με, which is comparable with that of commercial metal-foil sensors that need connection wires. More importantly, the FMR strain sensor shows a sensitivity of 65.46 ppm/με, indicating more than a 60 fold improvement than that of traditional wireless strain sensors based on patch antenna and RLC resonators whose frequency shift is mainly due to the strain induced dimension change. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramic (1 - x)Bi(Sc3/4In1/4)O3-xPbTiO3 (BSIPT) (0.45 ≤ x ≤ 0.70) solid solutions near the morphotropic phase boundary (MPB) were developed for high temperature piezoelectric transducer and actuator applications. It was found that the MPB composition of BSIPT ceramics was in the vicinity of x = 0.6, where it had relatively small tolerance factor t = 0.901 resulting in a high TC of 457 °C, and also optimal properties such as the high Pr = 25.4 μC/cm2, &eh;r = 1153, d33 = 201 pC/N, kp = 0.34, and the low Ec = 23.5 kV/cm. Measurements also showed that the depoling temperature was 360 °C, about 200 °C higher than that of commercialized PZT ceramics, which indicated good temperature stability. BSIPT ceramics are promising candidates for high temperature applications. [ABSTRACT FROM AUTHOR]

Voltage control of perpendicular magnetic anisotropy (PMA) in ferromagnetic/ferroelectric multiferroic heterostructures is a promising method to enable high density and low power perpendicular magnetic information storage. In this study, we successfully achieved large voltage tuning of PMA at room temperature in (Co/Pt)3/Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) multiferroic heterostructures. Voltage tuning of magnetic anisotropy and the magnetoelectric coupling effect has been qualitatively studied by ferromagnetic resonance, and the multiferroic heterostructure could be reversibly flipped between two distinct PMA states under zero or high electric fields. During the linear piezo-strain response of PZN-PT, the multiferroic heterostructures exhibit small magnetoelectric coupling and the electric field-induced magnetic anisotropy field was about 295 Oe. During the electric field-induced phase transition of PZN-PT, voltage tuning of PMA enhanced more than two times that of the first linear region and the electric field-induced magnetic anisotropy field increased to 634 Oe. Finally, this magnetoelectric coupling was enhanced to 672 Oe by applying 12 kV/cm, corresponding to a large magnetoelectric coupling coefficient up to 56 Oe·cm/kV. Benefiting from the giant strain response during voltage-induced phase transition in PZN-PT, voltage tuning of PMA in those multiferroic heterostructures is a promising candidate for power-efficient magnetic memories. [ABSTRACT FROM AUTHOR]

Rayleigh analysis has been used to investigate the temperature dependence of the dielectric response of relaxor ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 films grown on platinized silicon substrates by chemical solution deposition. The irreversible contribution to dielectric permittivity maximizes at 50 °C and decreases with further temperature increase; while the intrinsic/reversible contribution is weakly dependent on temperature. The relaxor ferroelectric transition temperature Tm increases from 160 °C to 172 °C when the frequency increases from 1 kHz to 100 kHz. The dielectric nonlinearity decreases with temperature: falling from 0.012 cm/kV at room temperature to 0.005 cm/kV at 225 °C in tests at 1 kHz. [ABSTRACT FROM AUTHOR]

We report the epitaxial growth of multiferroic BiFeO3 (BFO) film on Si(001) substrate by pulsed laser deposition using CeO2/yttria-stabilized zirconia (YSZ) as buffer layers. The epitaxial relationships of the films were BFO(001)/CeO2(001)/YSZ(001)/Si(001) for out-of-plane and [110]BFO|[100]CeO2|[100]YSZ|[100]Si for in-plane, respectively. Capacitance-voltage characteristics of a Pt/BFO/CeO2/YSZ/p-Si capacitor exhibited clockwise hysteresis loops with a large memory window of 2.5 V at sweeping voltages of ±16 V. Both the high and low capacitance values showed no obvious degradation after 104 s. The improved retention property was attributed to the use of high-k CeO2/YSZ insulating layers that effectively eliminated the charge trapping in the heterostructure. [ABSTRACT FROM AUTHOR]

The dielectric properties of lead lanthanum zirconate titanate (PLZT) thin films on platinized silicon (Pt/Si) with and without ZrO2 insertion layers were investigated in the temperature range from 20 °C to 300 °C. Permittivity, dielectric loss tangent, and tunability were reduced for the samples with ZrO2 insertion layers compared to those without the layers. Additionally, the permittivity was less dependent on frequency over the broad temperature range studied (20-300 °C). The leakage current behavior of the PLZT films with and without ZrO2 insertion layers was also investigated, and on the basis of those results, a probable conduction mechanism has been suggested. The improved electrical properties in the PLZT with ZrO2 layers are attributed to the ZrO2 layer blocking the mobile ionic defects and reducing free charge carriers to transport. [ABSTRACT FROM AUTHOR]

High-valence Pr-doped BiFeO3 (BPF) multiferroic thin film was prepared by pulsed laser deposition on a Pt/TiO2/SiO2/Si substrate. X-ray diffraction analysis indicates that the BPF film is of pure phase with a polycrystalline perovskite structure. The BPF film exhibited enhanced multiferroic properties: (i) a rectangular-shaped electric hysteresis loop with a large Pr of 75 μC/cm2 and a low Ec of 250 kV/cm at Emax ∼620 kV/cm, (ii) a saturated magnetic hysteresis loop with a large Ms of 58 emu/cm3, and (iii) a fatigue-free behavior after being subjected to 1.2×109 switching cycles, which were superior to, in some aspects, those of La- or Nd-doped BiFeO3 films reported before. [ABSTRACT FROM AUTHOR]

We report a continuously tunable resistive switching behavior in Pt/BiFeO3/Nb-doped SrTiO3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 × 105% by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO3/Nb-doped SrTiO3 interface. [ABSTRACT FROM AUTHOR]

Ferroelectric Pb0.92La0.08Zr0.52Ti0.48Oδ films (≈2-μm thickness) were grown on LaNiO3-buffered nickel foils by chemical solution deposition. Their ferroelectric and dielectric properties were measured as a function of temperature. With increasing temperature from room temperature to 200 °C, back-switching polarization increased while spontaneous polarization, remanent polarization, and coercive field decreased. The domain wall energy barrier was determined from the temperature-dependent back-switching polarization. Decreased irreversible/extrinsic and reversible/intrinsic dielectric responses were observed with increasing frequency. The ratio of irreversible to reversible contributions to dielectric nonlinearity was analyzed by the Rayleigh law. This ratio decreased with increasing frequency from 500 Hz to 500 kHz. [ABSTRACT FROM AUTHOR]