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In spite of the excellent electrochemical performance in lithium-ion batteries (LIBs), transition-metal compounds usually show inferior capacity and cyclability in sodium-ion batteries (SIBs), implying different reaction schemes between these two types of systems. Herein, coupling operando magnetometry with electrochemical measurement, we peformed a comprehensive investigation on the intrinsic relationship between the ion-embedding mechanisms and the electrochemical properties of the typical FeS2/Na (Li) cells. Operando magnetometry together with ex-situ transmission electron microscopy (TEM) measurement reveal that only part of FeS2 is involved in the conversion reaction process, while the unreactive parts form "inactive cores" that lead to the low capacity. Through quantification with Langevin fitting, we further show that the size of the iron grains produced by the conversion reaction are much smaller in SIBs than that in LIBs, which may lead to more serious pulverization, thereby resulting in worse cycle performance. The underlying reason for the above two above phenomena in SIBs is the sluggish kinetics caused by the larger Na-ion radius. Our work paves a new way for the investigation of novel SIB materials with high capacity and long durability.

With the rapid development of artificial intelligence and wearable devices, flexible magnetic sensors have attracted much attention in recent years. In this work, large self-biased 0–3 type poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite (P(VDF-TrFE)/CoFe2O4) flexible magnetoelectric (ME) composite films are proposed for the development of AC magnetic sensors. P(VDF-TrFE)/CoFe2O4 composite films with CoFe2O4 nanoparticle mass contents from 5 to 30% are successfully fabricated through the solution casting method. The results show that the nanoparticles are homogeneously dispersed in the P(VDF-TrFE) matrix, and the composite films have both excellent ferroelectric and ferromagnetic properties. The P(VDF-TrFE)/CoFe2O4 composite films all exhibit a large ME effect. The ME coefficient reaches 47.1 mV·cm−1·Oe−1 for the film with a CoFe2O4 nanoparticle mass content of 20% at resonance frequency. Moreover, the composite films have a large self-biased ME effect with a maximum value of 20.4 mV·cm−1·Oe−1, which is mainly due to the high remnant magnetization of CoFe2O4 nanoparticles. To evaluate the composite films for application in magnetic sensors, the response of the ME output voltage to an AC magnetic field without a bias DC magnetic field was measured. The good linear correlation coefficient, sensitivity and repeatability indicate that the proposed 0–3 type P(VDF-TrFE)/CoFe2O4 composite film is a promising material for flexible AC magnetic sensors.

We investigated femto- and picosecond-time magnetization dynamics in a ferromagnetic Ni80Fe20 film with varying thicknesses (wedge-shaped film). We observed that the thickness gradient strongly affects the magnetic moment distribution, causing a magnetization reorientation from in-plane to out-of-plane, and formatting a stripe domain (SD) at the thicker end of the wedge. The magnetization dynamics measurements reveal that the part of the film displaying SDs follows a substantially faster demagnetization and magnetization recovery and smaller magnetization quenching compared to the in-plane domain film. The experiments and micromagnetic simulations support that the decrease in relaxation time is caused by a magnetic anisotropy of the films introduced by SD formation. Our results point out that the micromagnetic structure plays an important role in the magnetization dynamics in ferromagnetic films after optically triggered demagnetization.

The influence of La3+-doping on the electrocaloric effect (ECE) of the 0.75(Pb1-3x/2Lax)(Mg1/3Nb2/3)O3-0.25(Pb1-3x/2Lax)TiO3 (L-PMN-PT: x/75/25 x = 0.0–4.0 mol.%) ceramics was studied. With the increase of La3+-doping in these ceramics, the relaxor ferroelectric properties increase, while the average grain size, coercive field E c and Curie temperature T C decrease. As a result, a maximum adiabatic temperature change Δ T as high as 0.68 K, measured by direct measurement method, was achieved under a lower electric field ( E ) intensity of 5 kV/mm at 383 K for samples with x = 2.0 mol.%. Besides the high Δ T value, the La3+-doping also leads to a temperature insensitivity of ΔT. The variation of Δ T is less than 0.15 K, or 28.3%, over a wide temperature range of 303–423 K. The La3+-doped PMN-PT ceramics, with large and temperature insensitive Δ T over a broad temperature range, is very helpful for practical application. The reduction of E c and T C can be attributed to the suppression of long-range coupling between oxygen octahedrons due to the partial replacement of Pb2+ by La3+. The temperature insensitivity of ECE is attributed to the enhancement of relaxor ferroelectric properties.

The pseudo-first-order phase transition in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics leads to a sharp increase in temperature change (ΔT) in the vicinity of the ferroelectric-to-relaxor transition temperature TFR (~100 °C) [Appl. Phys. Lett. 110 (2017) 182904]. In this study, we add the 0.78Bi0.5Na0.5TiO3-0.06BaTiO3-0.16(Sr0.7Bi0.2)TiO3 relaxor phase to the 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ferroelectric matrix to tune its electrocaloric effect. The results show that the addition of the relaxor phase plays a vital role in phase and local-structure evolution. A transition occurs between the ferroelectric and ergodic relaxor phases when the mass fraction of the latter increases to 30% (x = 0.3), as verified by X-ray diffraction analysis, Raman spectroscopy, and polarization-electric field (P-E) hysteresis loops. Furthermore, addition of the relaxor phase reduces the TFR from 76 °C at x = 0.1–55 °C at x = 0.2; however, this transition disappears at x = 0.3 and 0.4 composite. In-situ piezo-force microscopy (PFM) images illustrate that domains can be written into x = 0.1 and 0.2 ceramics with a valley in the piezoresponse curves. Increasing the temperature agitates the domain arrangement and decreases the contrast for PFM images; this indicates a gradual phase transition in the composite. The temperature corresponding to maximum ΔT exhibits a downward shift (0.58 K at 80 °C for x = 0.1 and 0.5 K at 65 °C for x = 0.2), while the temperature-ΔT curves are flat when x = 0.3 and 0.4. Moreover, the maximum ΔT shows a decrease with an increase in the relaxor phase content; this is believed to be related to a decrease in the latent heat due to a pseudo-first-order to second-order transition. Thus, we suggest that the incorporation of a relaxor phase into ferroelectric matrices is an effective technique to tune their electrocaloric effect and improve the thermal stability of ceramic composites.

We report the influence of different annealing temperatures on the magnetic property of FeGa thin films. The measurement was done for the film thickness from 42 to 420 nm. Our results show that the annealing temperature affects not only the microstructure but also the ferromagnetic resonance signal of the film. Annealing of a FeGa film improves the in-plane remanence ratio and reduces the in-plane ferromagnetic resonance linewidth by a factor of five. This annealing treatment promotes film texture and releases compressive stresses in the film. Our results demonstrate that the structural control via annealing is viable. The necessary magnetic softness of the FeGa film for microwave applications can be achieved.

We investigated the magnetization dynamics of the 350 nm permalloy film with in plane domain (IPD), stripe domain (SD), and labyrinth domain (LD) patterns. Experimental and micromagnetic simulation results showed that the change in magnetic domain structure from IPD to LD was due to the increasing perpendicular magnetic anisotropy (PMA) of the film. The magnetization dynamics indicated that the resonant modes of the film strongly depended on the magnetic domain structure. IPD films presented a uniform precession mode. The film with well-regular SD exhibited clear acoustic and optical resonance modes, and the formation of LD suppressed both resonance modes. Finally, the dynamics of magnetization dependent on the domain structure in these films were discussed by using the phenomenological resonance models.

In spite of the excellent electrochemical performance in lithium-ion batteries (LIBs), transition-metal compounds usually show inferior capacity and cyclability in sodium-ion batteries (SIBs), implying different reaction schemes between these two types of systems. Herein, coupling operando magnetometry with electrochemical measurement, we peformed a comprehensive investigation on the intrinsic relationship between the ion-embedding mechanisms and the electrochemical properties of the typical FeS

Owing to their low cost and abundant reserves relative to conventional lithium-ion batteries (LIBs), potassium-ion batteries (PIBs), and aluminum-ion batteries (AIBs) have shown appealing potential for electrochemical energy storage, but progress so far has been limited by the lack of suitable electrode materials. In this work, we demonstrated a facile strategy to achieve highly reversible potassium and aluminum ions storage in strongly coupled nanosized MoSe2@carbon matrix, induced through an ion complexation strategy. We present a broad range of electrochemical characterization of the synthesized product that exhibits high specific capacities, good rate capability, and excellent cycling stability toward PIBs and AIBs. Through a series of systematic ex situ X-ray photoelectron spectroscopy (XPS) characterizations and density functional theory (DFT) calculations, the Al3+ intercalation mechanism of MoSe2-based AIBs are elucidated. Moreover, both the assembled PIBs and AIBs worked well when exposed to low and high temperatures within the range of -10 to 50 °C, showing promise for energy storage devices in harsh environment. The present study provides new insights into the exploration of MoSe2 as high-performance electrode materials for PIBs and AIBs.

The development of new rechargeable metal-ion (Na+, K+ or Al3+) batteries (MIBs) with high performance would break the global monopoly on lithium-ion batteries (LIBs). However, because of the larger ionic sizes of Na+, K+ and Al3+ in comparison to Li+, the requirement of electrode materials with suitable tunnels for these metal ions insertion/extraction is more stringent. Over years, a large number of electrodes materials are studied and optimized for a specific type of MIB, yet a universal suitable candidate that can be applied for all of them still remains scarce. Here we report a solvothermal method coupled with the sulfidation strategy to engineer novel multi-layer architecture of FeS2@C hybrids which is constructed from building blocks of ultrathin nanoflakes, favoring fast electrochemical energy storage. Electrochemical measurements show that the multi-layer structured FeS2@C hybrids enables reversible sodium-, potassium- and aluminum-ion storage process with high specific capacities, excellent rate capability and outstanding cycling stability. We hope that this research will inspire new ideas for developing various electrode materials for high-performance MIBs.

Transition-metal phosphides have a potential application in lithium-ion batteries (LIBs) because of their high theoretical capacities and low cost; nevertheless, they possess dramatic volumetric variation during cycling associated with poor conductivity, limiting their practical applications. Here, a three-dimensional (3D) hierarchical flowerlike FeP coated with nitrogen-doped carbon layer (FeP@N,C hybrid) was constructed through a solvothermal method, followed by a phosphating approach under low temperature. N-doped carbon not only suppresses the volume fluctuation of FeP, but also promotes electron transfer, accompanied by catalyzing the decomposition of Li3P to improve the reversibility of the FeP@N,C hybrid during cycling processes. In addition, a 3D flowerlike architecture assembled from porous nanosheets is also beneficial for shortening the migration path of ions as well as improving the contact area of electrode with electrolyte, which enhances the reaction kinetics and is proved by both experimental measurement of Li+ diffusion coefficient and resistivity, along with the calculation of density functional theory. Consequently, the 3D hierarchical flowerlike FeP@N,C hybrid performs excellent cyclic stability (569 mA h g-1 at a current density of 500 mA g-1 for the 300th cycle) and rate performance (331.94 mA h g-1 at a high current density of 5 A g-1) for LIBs. Based on above results, the fabrication strategy in this work could offer a thought to design other high-performance metal phosphide hybrids.

Electrocaloric effect (ECE) offers a promising method for highly efficient and environment-friendly solid-state refrigeration. To obtain giant EC temperature change (ΔT), high electric field and temperature are usually applied to ECE materials, but few investigations have been done on the influence of Joule heating on ECE caused by leakage current at high electric field and temperature. In this paper, ECE, leakage current and Joule heating of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (0.5BZT-0.5BCT) ceramic were studied in the wide electric field and temperature range. The distortion of ECE curves at high electric field and temperature is proved to be caused by Joule heating which makes a negative effect on ECE refrigeration. The effective temperature change (ΔTeff) was defined, and the difference among ΔTeff, EC temperature change measured directly (ΔTD), and the intrinsic EC temperature change (ΔTECE) was discussed in detail. The results provide a guiding significance to the investigation of ECE and electronic materials.

The soft magnetic films (SMFs) using in monolithic microwave integrated circuits (MMICs) are suffered from the lower ferromagnetic resonance frequency f FMR and resistivity. In this study, Fe0.5Co0.5-ZnO films with high resistivity were fabricated by a compositional gradient sputtering on (0 1 1) lead zinc niobate–lead titanate (PZN-PT) substrates. It is interesting to note that the resistivity of the ZnO-doped Fe0.5Co0.5 films is 10–30 times larger than that of pure Fe0.5Co0.5 films. An ultrahigh f FMR of 10.48 GHz were achieved at electric field of 8 kV/cm without bias magnetic field. The excellent microwave ferromagnetic performances in as-deposited films can be attributed to two reasons: (1) the large uniaxial anisotropy field induced by gradient composition of doping ZnO, (2) the strong magnetoelectric coupling between the ferromagnetic/ferrielectric interfaces under the condition of high resistivity in Fe0.5Co0.5-ZnO films.

FeNi films with different phase structures were prepared by electrodeposition method, and the phase structure of the film was controlled by the composition of the film. The results indicated that the well-defined stripe domain patterns and good magnetic properties of the films were fond of the bcc and bcc + fcc phase structures of the FeNi films. The results of permeability spectra indicated that the acoustic and optical modes of the film could be changed by the direction of the microwave field and stripe domain. FeNi stripe domain films exhibited the different frequency under the two modes, and the acoustic and optical modes of film showed obvious spectra in the bcc and bcc + fcc phases of FeNi films. The results are helpful to the development of the stripe domain optical mode microwave devices.

Excess Bi2O3 was added to 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramic and the evolution of dielectric, electromechanical properties and electrocaloric effect (ECE) were studied. With increasing Bi2O3 addition, the nonergodic relaxor phase transformed to ergodic relaxor phase. The XRD patterns and Raman spectroscopy show the increasing relaxor properties with excess Bi2O3 doping. The Bi0.53Na0.5TiO3-BaTiO3 ceramic exhibited a temperature insensitive ECE with an “Λ” type, the variation of which was less than 26% over 30 ~ 120 °C. The temperature stability of ECE for Bi0.53Na0.5TiO3-BaTiO3 ceramic was related with the characteristics of ergodic relaxor phase, which was clarified by structural and Raman spectroscopy analysis.

Polyoxometalate (POM) as an "electronic sponge" can store a great number of electrons; however, shortcomings of poor conductivity and solubility in electrolytes cause a significant decrease in specific capacity and poor rate capability. To address the aforementioned disadvantages, a dual strategy was proposed, including coating the conductive polypyrrole (PPy) and utilizing nitrogenous ligands (1,10-phenanthroline monohydrate = 1,10-phen) for metal-organic frameworks (MOFs) to fabricate a [Cu(1,10-phen)(H2O)2]2[Mo6O20]@PPy (Cu-POMOF@PPy) composite, effectively confining the POM in MOFs to avoid dissolution of POM in the electrolyte and improve electrochemical stability. Simultaneously, the PPy shell could improve the conductivity, contribute extra capacity, and alleviate volume variation of Cu-POMOF during cycling. Therefore, the final Cu-POMOF@PPy composite provides an excellent specific capacity of around 769 mA h g-1 at 0.1 A g-1 after 160 cycles and good rate performance, associated with great cycling stability (319 mA h g-1 at 2 A g-1 after 500 cycles). Moreover, the electrochemical reaction mechanism of Cu-POMOF@PPy was investigated by ex situ XPS measurements, indicating that storage of electrons results from the reduction/oxidation of Mo atoms (Mo6+ ↔ Mo4+) and Cu atoms (Cu2+ ↔ Cu0). As a consequence, this work not only proposes a novel method for preparing POM-based lithium-ion batteries but also expands the variety of anode materials.

Magnetoelectric (ME) coupling has gradually developed into one of the core means of advancing ultralow-power memory, logic and sensor technologies. Among various strategies, magneto-ionic control of magnetism based on mechanism such as redox, intercalation/deintercalation, and charge accumulation can be achieved in ion battery or capacitor systems. In this work, we demonstrate a ME effect originating from the spin capacitance, combining the advantages of intercalation batteries and supercapacitors. A giant, fast and reversible modulation on the saturation magnetization of ferromagnetic Fe is achieved by lithium ions motion across the Fe/Li2O interface at no more than 1 V. Furthermore, the magnetic evolution driven by the conversion reaction between FeO and Fe over a larger voltage range demonstrates ferromagnetic ordering of the FeO surface. These findings not only open new perspectives for developing high-performance magneto-ionic devices, but also are crucial to designing spintronic devices composed of iron and oxide multilayer structures.

This paper presents a novel dual-band helix antenna operating at HBC band. Two helixes are adopted to excite two resonances. One helix is fed by 50Ω port. The other one is excited by a short pin. The bandwidth of the proposed antenna covers 18.5-19.8 and 24.4-25.5 MHz.

The manipulation of magnetism by electrical means is one of the most intensely pursued research topics of recent times aiming at the development of efficient and low-energy consumption devices in spintronics, microelectronics and bioelectronics. Herein, we successfully tuned the saturated magnetization of Fe

In this work, an arc-shaped Metglas/polyvinylidene fluoride (PVDF)/Ni laminate is proposed, which exhibits a large self-biased magnetoelectric (ME) effect due to the internal magnetization gradient field between the two magnetic layers and the built-in stress formed from the arc-shaped structure. The ME coefficients reach 38.24 and 15.0 V cm−1 Oe−1 without a DC bias magnetic field at resonance and nonresonant frequencies, respectively. The sample shows a high sensitivity, resolution and linearity with values of 210.07 mV Oe−1, 1 nT and 0.9999 at the resonance frequency, respectively. The sample was then used to detect AC magnetic fields with different nonresonant frequencies (ranging from 1 to 25 kHz), resulting in the measured data being in good agreement with the actual data. Under a zero bias magnetic field and at frequencies of 40 and 1 Hz, the limit of detection can reach 2 and 8 nT, and the resolution can reach 1 and 4 nT, respectively. The results indicate that the arc-shaped Metglas/PVDF/Ni laminate shows a large self-biased ME effect and good AC magnetic sensing performance in the bending state, which provides a new way to develop a wide frequency range AC magnetic sensor.