Magnetoelectric Films Research Articles

Antiferromagnetic Nanoscale Bit Arrays of Magnetoelectric Cr2O3 Thin Films.

Magnetism of oxide antiferromagnets (AFMs) has been studied in single crystals and extended thin films. The properties of AFM nanostructures still remain underexplored. Here, we report on the fabrication and magnetic imaging of granular 100 nm-thick magnetoelectric Cr2O3 films patterned in circular bits with diameters ranging from 500 down to 100 nm. With the change of the lateral size, the domain structure evolves from a multidomain state for larger bits to a single domain state for the smallest bits. Based on spin-lattice simulations, we show that the physics of the domain pattern formation in granular AFM bits is primarily determined by the energy dissipation upon cooling, which results in motion and expelling of AFM domain walls of the bit. Our results provide a way toward the fabrication of single domain AFM-bit-patterned memory devices and the exploration of the interplay between AFM nanostructures and their geometric shape.

Performance optimization for magnetoelectric antennas based on a multi-field coupling analysis model

This paper presents a multi-field coupling model for magnetoelectric (ME) antennas, encompassing a ME film, electrode layers, and a substrate featuring a cavity structure. This model accounts for the nonlinear magnetoelastic coupling within the radiation layer and employs a combined DC and AC simulation methodology to capture the antenna's radiation mechanism. Leveraging this multi-field coupling model, performance differences between the ME antenna and an ideal ME composite film are analyzed. By exploring optimization schemes based on multi-physics fields, electrode materials, and structural design, the ME antenna's radiation performance is significantly enhanced. The findings demonstrate that the complete antenna structure, with its increased thickness and cavity design, exhibits a lower resonance frequency and a higher converse ME (CME) coefficient compared to the ideal ME film. The optimal CME effect is achieved under proper external stimuli, leading to a broader 3 dB bandwidth. Expanding the cavity dimensions enhances the CME coefficient by 42% and reduces the resonance frequency due to decreased acoustic wave loss. Adopting electrode materials with higher acoustic impedance elevates the CME coefficient, yet narrows the bandwidth. Conversely, using silver (Ag) electrodes promotes a broader bandwidth. Additionally, ME antenna arrays are designed to broaden the bandwidth by 300%.

Large room temperature magnetoelectric response in quasi 1–2 nanocomposite films on mica substrate

AbstractA novel quasi 1–2 type magnetoelectric (ME) nanocomposite films composted of one‐dimensional CoFe2O4 nanofibers and two‐dimensional PbZr0.2Ti0.8O3 films on flexible mica substrate have been designed and fabricated. The ME coupling effects have been greatly enhanced due to the release of the clamping effect and the high strain transfer efficiency between the large aspect ratio of the nanofibers and ferroelectric thin films. The release of the clamping effect was confirmed by reducing the thickness of the mica substrate, in which the piezoelectric coefficient and ME coupling coefficient of the nanocomposite films have been greatly boosted by the decrease in the mica thickness. A large direct ME coupling coefficient of 630 mV/(cm Oe) and a converse ME coupling coefficient of 1.43 × 10−8 s/m have been achieved in the quasi 1–2 nanocomposite film with a substrate thickness of 25 µm. Furthermore, the stain‐mediated ME coupling was revealed by magnetic field/electric field‐induced local ferroelectric/magnetic domain switching dynamics.

Gisterezis namagnichennosti i elektricheskoy polyarizatsii v magnitnykh nanostrukturakh so vzaimodeystviem Dzyaloshinskogo-Moriya

The influence of the Dzyaloshinskii–Moriya interaction (DMI) on the formation of polar structures in nanoscale magnetoelectric films has been studied. The sequence of micromagnetic structures of different topology at magnetization and remagnetization of a film of limited size in a magnetic field oriented along the normal to the film surface is investigated. It is shown that the formation of polar structures is related to the existence of magnetic structures. Specific features of polar states in dependence of the DMI type and the interface symmetry is analyzed.

Intense Pulsed Light Thermal Treatment of Pb(Zr,Ti)O3 /Metglas Heterostructured Films Resulting in Extreme Magnetoelectric Coupling of over 20Vcm-1 Oe-1.

Magnetoelectric (ME) film composites consisting of piezoelectric and magnetostrictive materials are promising candidates for application in magnetic field sensors, energy harvesters, and ME antennas. Conventionally, high-temperature annealing is required to crystallize piezoelectric films, restricting the use of heat-sensitive magnetostrictive substrates that enhance ME coupling. Herein, a synergetic approach is demonstrated for fabricating ME film composites that combines aerosol deposition and instantaneous thermal treatment based on intense pulsed light (IPL) radiation to form piezoelectric Pb(Zr,Ti)O3 (PZT) thick films on an amorphous Metglas substrate. IPL rapidly anneals PZT films within a few milliseconds without damaging the underlying Metglas. To optimize the IPL irradiation conditions, the temperature distribution inside the PZT/Metglas film is determined using transient photothermal computational simulation. The PZT/Metglas films are annealed using different IPL pulse durations to determine the structure-property relationship. IPL treatment results in an enhanced crystallinity of the PZT, thus improving the dielectric, piezoelectric, and ME properties of the composite films. An ultrahigh off-resonance ME coupling (≈20Vcm-1 Oe-1 ) is obtained for the PZT/Metglas film that is IPL annealed at a pulse width of 0.75ms (an order of magnitude higher than that reported for other ME films), confirming the potential for next-generation, miniaturized, and high-performance ME devices.

Stability of a skyrmion crystal in a frustrated antiferromagnetic bilayer on a triangular lattice

We studied the processes of formation and conditions of stability of skyrmion lattices during thermodynamic fluctuations in magnetoelectric films, namely, in a frustrated antiferromagnetic/ferroelectric bilayer on a triangular lattice. We calculate the ground state configurations with given parameters using the steepest descent method. We consider the thermodynamic fluctuations in influence of an external magnetic field on the ground state configurations and phase transitions occurring in the model using Monte Carlo simulation.

Magnetodielectric and TMR effects in P(VDF-HFP)/SrFe12O19 composite films for magnetic field – Tuned photodetector application

Magnetoelectric (ME) multiferroic materials possess extensive research interest as a result of their use in a variety of sectors. In this work, the optical properties of plain P(VDF-HFP) film and P(VDF-HFP)/SrFe12O19 composite films are investigated through UV-Vis absorption spectroscopy. In addition, the ME coupling of SrFe12O19 nanofibers reinforced P(VDF-HFP) composite films is investigated though magnetodielectric (MD) measurements. The parameters such as dielectric constant, capacitance, dielectric loss and impedance of the composite films are found to change with the applied magnetic field which is attributed to the direct ME coupling of the composite films. The prepared ME films show a negative tunneling magnetoresistance (TMR) effect with maximum TMR% of 14 % for the film (PSNF20) with 20 wt% of SrFe12O19 nanofiber loading. Photodetectors are fabricated using the films as active elements and the performance of the photodetectors is studied under various intensities of visible light radiation. All the devices exhibit good photosensitivity, responsivity and specific detectivity at an illumination intensity of 20 mW/cm2. The photodetector (PD20) fabricated using PSNF20 as an active element has the maximum rise/decay time, photosensitivity, responsivity and specific detectivity values as 468 /553 ms, 2.7 × 103, 22 mA/W and 6.77 × 1013 Jones, respectively at 20 mW/cm2. In addition, the performance of the devices is analyzed by subjecting the active element to external magnetic field. The photosensitivity, responsivity and specific detectivity all improve, showing that the magnetic field has an effect on the photodetector. The above parameters are maximum for PD20 device and the values are 4.3 × 103, 26 mA/W and, 8.01 × 1013 Jones, respectively at 4000 Oe and 20 mW/cm2. Thus, the prepared flexible magnetoelectric films of P(VDF-HFP)/SrFe12O19 nanofiber composites have been shown to be good options for the magnetic field tuned photodetector applications such as environmental sensing monitor, safety and security, optical communication systems, magnetic sensors, piezoelectric sensors and spintronics devices.

Quasi-static modulation of multiferroic properties in flexible magnetoelectric Cr2O3/muscovite heteroepitaxy

Due to the strong coupling between electrical polarization and magnetization, magnetoelectric materials show promising features for low-power spintronics and ultra-sensitive magnetic sensors. Compared to the conventional tunning of magnetoelectricity, this work presents a modulation of magnetic and electric orders in magnetoelectric material through a quasi-static mechanical strain. To acquire this, linear magnetoelectric Cr2O3 film is fabricated epitaxially on muscovite substrates. Taking the natural flexibility of muscovite, applying a strain to the heterostructure is feasible via mechanical bending. In the bending experiment, the magnetization of Cr2O3 film can be enhanced significantly, and the techniques of X-ray absorption dichroism unveil insights with support from theoretical predictions. Besides, the electric polarization and magnetoelectric coupling of Cr2O3 can also be adjusted by mechanical bending. This work offers a comprehensive understanding of the relationship between quasi-static strain and magnetic and electrical behaviors and opens a new aspect of the combination between magnetoelectric materials and flexible substrates for future development.

Room-temperature multiferroicity and magnetoelectric couplings in (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 spinel films

The electric field manipulation of a magnetic order is a key feature of advanced information technologies and the development of room-temperature multiferroic magnetoelectrics remains an important task. In this work, we report novel single-phase magnetoelectric (ME) films consisting of a (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 spinel ferrite. The (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 thin films display a switchable polarization and magnetization with a remnant polarization of about 2.1 µC cm–2 and a remnant magnetization of about 82.0 emu cm–3 at 300 K. Electric field control of magnetism is detected, the magnetization modulation reaches 8.5 % at room temperature with an electric field of 500 kV cm−1, revealing the existence of magnetoelectric coupling. We believe that the substitutions of Al3+ and Mg2+ cations at the spinel sublattices might induce local distortions and local electric field and modulate the superexchange interactions between magnetic ions, which give rise to the ferroelectricity and ME effect in the (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 thin films. The electric field-induced charge modulation may also contribute to the observed magnetoelectric effect, which likely results from the migration and redistribution of oxygen vacancies in the prepared nanofilms. The findings of this work can stimulate research studies on the development of room temperature multiferroics and magnetoelectrics based on the spinel ferrite compounds.

An Optically, Electrically, Magnetically Controllable Dual‐Gate Phototransistor

AbstractHigher data transmission rates, broader bandwidths, better privacy, and security are indispensable for the current information‐explosive age. However, to achieve the desired functionalities still remains as a great challenge. In this study, a two‐terminal, vertical dual‐gate phototransistor, which can be controlled by light, electric and magnetic fields, is proposed, fabricated, and demonstrated. This phototransistor uses a tandem structure composed of an organic solar cell (OSC) of ITO/ZnO/P3HT:PC61BM/MoO3/Ag, a resistive random access memory (RRAM) of Ag/PMMA/Au and a magnetoelectric film with micropyramid structure of PDMS:FeNi/silver nanowires (AgNWs). This device integrates and couples the properties of each individual component enabling to respond to light, electric and magnetic fields and works as a dual‐gate transistor. Compared with conventional transistors, the proposed device carries several intriguing features, such as ultrafast photoresponse time of 3 µs, controllable photocurrent with a variety of external stimuli, high ON/OFF ratio greater than 103, and touchless human–machine interaction. All of the above features are beneficial for high‐speed optical communication and circuit miniaturization. Furthermore, its unique logical characteristics show great potential for information security in the future development of Li‐Fi optical communication.

Magnetoelectric Bio-Implants Powered and Programmed by a Single Transmitter for Coordinated Multisite Stimulation.

This paper presents a hardware platform including stimulating implants wirelessly powered and controlled by a shared transmitter for coordinated leadless multisite stimulation. The adopted novel single-transmitter, multiple-implant structure can flexibly deploy stimuli, improve system efficiency, easily scale stimulating channel quantity and relieve efforts in device synchronization. In the proposed system, a wireless link leveraging magnetoelectric effects is co-designed with a robust and efficient system-on-chip to enable reliable operation and individual programming of every implant. Each implant integrates a 0.8-mm2 chip, a 6-mm2 magnetoelectric film, and an energy storage capacitor within a 6.2-mm3 size. Magnetoelectric power transfer is capable of safely transmitting milliwatt power to devices placed several centimeters away from the transmitter coil, maintaining good efficiency with size constraints and tolerating 60-degree, 1.5-cm misalignment in angular and lateral movement. The SoC robustly operates with 2-V source amplitude variations that spans a 40-mm transmitter-implant distance change, realizes individual addressability through physical unclonable function IDs, and achieves 90% efficiency for 1.5-to-3.5-V stimulation with fully programmable stimulation parameters.

Magnetic Skyrmions and Phase Transitions in Antiferromagnetic/Ferroelectric Bilayers

We study in this paper the ground state and the properties of a skyrmions in magnetoelectric films, namely antiferromagnetic/ferroelectric superlattices in a support by steepest descent method and extensive Monte Carlo simulation. The ground state and ordering of the frustrated both classical Heisenberg and Ising models on the simple cubic lattice with a magnetoelectric coupling are studied under magnetic field.

Ferromagnetic, ferroelectric, and magnetoelectric properties in individual nanotube-based magnetoelectric films of CoFe2O4/BaTiO3 using electrically resistive core-shell magnetostrictive nanoparticles

Since 2010, two-phase magnetoelectric (ME) films consisting of magnetostrictive and piezoelectric phases have been continuously developed with regard to their promising ME responses, for potential applications such as ultra-sensitive magnetic sensing, magnetic-field induced energy harvesting, and nano-transduction. Generally, one-dimensional piezoelectric nanowires, nanorods, and nanotubes are used to enlarge the active area for strain transfer between the piezoelectric and magnetostrictive phases of ME films. In this study, we developed 1–2 type individual nanotube-based ME films of CoFe2O4/BaTiO3 with main considerations in the optimization of magnetostrictive phase, piezoelectric phase, and interface between the phases, respectively. First, core-shell magnetostrictive nanoparticles were improved with a high resistivity of 3.89 MΩ·cm and saturation magnetization of 20.8 emu/g via a sufficient TiO2 coating on the CoFe2O4 nanoparticles. Then, individually free-standing TiOx nanotubes were prepared with an optimal structure exhibiting a large pore size of 220 nm and high interspace distance of 80 nm. Final 1–2 type ME films of CoFe2O4/BaTiO3 were successfully prepared by magnetostrictive particle electrodeposition and perovskite conversion in sequence. Enhanced dipole moments through high amounts of BaTiO3 phase were achieved with a maximal remnant polarization (Pr) of 0.192 µC/cm2 from the AC-electrodeposited (AC-) ME films exhibiting a dense film structure. Maximal ME coefficient of the AC-ME films was achieved with magnitude of 27.39 mV/cm∙Oe at Hbias = 1000 Oe. As a result, considering the investigations, the 1–2 type ME films could be expected for possible applications such as high-sensitive magnetic sensors or low-power energy harvesters.

Structure, electrical, optical and magnetoelectric properties of magnetron sputtered nanocrystalline NiFe/BaTiO3 thin films

BaTiO3 (BTO) and NiFe films grown on SrTiO3 (STO), Nb:SrTiO3 (NSTO), and ITO-glass substrates were prepared by radio-frequency (RF) and direct-current (DC) magnetron sputtering, respectively. The microstructure, ferroelectricity, leakage current, magnetoelectric (ME) coupling, ultraviolet–visible light spectrum, optical band gap, ellipsometry spectrum and surface morphology of the composite film are characterized by XRD, ferroelectric analyzer, ME coupling test system, U-4100, Horiba Smart SE and AFM. In addition, the stress, strain and piezoelectric voltage of the magnetoelectric composite film under the action of DC and AC magnetic fields are simulated by COMSOL multiphysics software. The experimental results show that the prepared composite film is polycrystalline, the surface roughness of the film is better, and the particles are uniform. The magnetoelectric coupling voltage gradually increases with the increase of the value of the DC magnetic field and the frequency of the AC magnetic field, and it has a larger absorption (about 0.3) at 340 nm. In addition, the simulation results also show the relationship between the coupling voltage VME and the applied magnetic field H.

Effect of the Two-Dimensional Magnetostrictive Fillers of CoFe2O4-Intercalated Graphene Oxide Sheets in 3-2 Type Poly(vinylidene fluoride)-Based Magnetoelectric Films.

In the last decade, magnetoelectric (ME) polymer films have been developed by including zero-dimensional or one-dimensional magnetostrictive fillers in a piezoelectric polymer matrix. Existing reports on ME polymer films reveal that the shape of the magnetostrictive fillers is a critical determinant of the polymeric phase conformation, strain transfer between the piezoelectric and magnetostrictive phases, and dipole alignment in the films. In this study, to investigate the effect of two-dimensional (2D) magnetostrictive fillers on piezoelectric, magnetic, and magnetoelectric responses, 3-2 type ME films were prepared using CoFe2O4-intercalated graphene oxide (CFO-i-GO) fillers and poly(vinylidene fluoride) (PVDF) polymers. The 2D fillers of CFO-i-GO were hydrothermally synthesized by CFO intercalation into the interlayers of GO sheets with different lateral sizes, which were controlled by ultrasonication treatment. It was found that the large-lateral-size GO (LGO), medium-lateral-size GO (MGO), and small-lateral-size GO (SGO) fillers in the PVDF-based ME films exhibited a lateral size effect on CFO intercalation, polymeric phase conformation, dipole alignment, and magnetoelectric responses. A maximum ME coefficient (αME) of 3.0 mV/cm∙Oe was achieved with a strong linearity (r2) of 0.9992 at an off-resonance frequency (f) of 1 kHz and applied direct current (dc) magnetic field (Hdc) of ± 1000 Oe. The 3-2 type polymer-based ME films with reliable ME responses have potential for use in high-feasibility ME devices for biomedical sensing applications.

Phonon polaritons in magnetoelectric multiferroics film: the possibility to drive surface modes using magnetic field

In this paper, we report our numerical study of transverse mode phonon polaritons generated on magnetoelectric multiferroic films. The mathematical models of the dispersion relation for both surface and guided-wave modes were derived by solving the Maxwell equations. Then, numerical calculations were performed for various thicknesses using parameters suitable for illustrating magnetoelectric multiferroic BaMnF4. It was found that around the thicknesses of 0.1 mm–1 mm, the guided-wave modes were discreet. The surface phonon polaritons were obtained at the region between ferroelectric resonant frequency ω e and intercept frequency ω i. These surface modes were reciprocal, i.e., ω( k ) = ω(− k ). These results were in good agreement with the calculated attenuated total reflection spectra. It was also found numerically that the application of a magnetic field was able to shift the frequency of the surface phonon polaritons.

MagNI: A Magnetoelectrically Powered and Controlled Wireless Neurostimulating Implant.

This paper presents the first wireless and programmable neural stimulator leveraging magnetoelectric (ME) effects for power and data transfer. Thanks to low tissue absorption, low misalignment sensitivity and high power transfer efficiency, the ME effect enables safe delivery of high power levels (a few milliwatts) at low resonant frequencies ( ∼250kHz) to mm-sized implants deep inside the body (30-mm depth). The presented MagNI (Magnetoelectric Neural Implant) consists of a 1.5-mm 2 180-nm CMOS chip, an in-house built 4×2mm ME film, an energy storage capacitor, and on-board electrodes on a flexible polyimide substrate with a total volume of 8.2mm 3. The chip with a power consumption of 23.7 μW includes robust system control and data recovery mechanisms under source amplitude variations (1-V variation tolerance). The system delivers fully-programmable bi-phasic current-controlled stimulation with patterns covering 0.05-to-1.5-mA amplitude, 64-to-512- μs pulse width, and 0-to-200-Hz repetition frequency for neurostimulation.

Large magnetodielectric effect based on spin-dependent charge transfer in metal–insulator type Co-(BaF2) nanogranular films

Cobalt-metal-fluoride nanogranular films exhibit high electrical resistivity (ρ) and high permittivity (ɛ′) as well as high magnetic moments, making them potentially suitable for applications in low power magnetoelectronic devices at a high-frequency range. Here, we present the DC/AC magnetoelectric effect of high-ρ Cox-(BaF2)1 − x nanogranular films that are constituted of Co nanogranules of about 2 nm in diameter in an insulating BaF2 crystal. Under the application of magnetic field (H), we observed the ρ variations (Δρ/ρ0) of 2.0%–5.9% for x ranging 0.19–0.54 and the ɛ′ variations (Δɛ/ε0′) of 0.7%–6.0% for x ranging 0.19–0.42, respectively. These magnetically controllable ρ and ɛ′ are realized based on the spin-dependent quantum-mechanical charge transfer. The Cox-(BaF2)1 − x film for x = 0.42 possesses high ρ, while remaining in a notably high Δɛ/ε0′ of 6% at a megahertz frequency range. This study demonstrates a candidate of high-resistive magnetoelectric nanogranular films, which may bring prosperous applications in high-frequency magnetoelectric devices with low power consumption.

Liquid Metal Based Stretchable Magnetoelectric Films and Their Capacity for Mechanoelectrical Conversion

AbstractGallium based liquid metal alloys (GLMAs) have tremendous prospects in diverse applications, such as transient devices, soft robotics, biomedical sensing, and health monitoring, due to being endowed with compelling deformability and conductivity simultaneously. Unfortunately, most GLMA‐based flexible devices require external power supply, which might cause some potential issues including additional weight, occupied space, and frequent replacement. Alternatively, self‐powered concepts, by biologically converting mechanical forces to electric energy, are deemed as a promising strategy. Thus, the challenge that GLMAs are applied to self‐powered system is critical and imperative. This study has demonstrated a self‐powered and stretchable magnetoelectric film based on GLMAs. The magnetoelectric film is able to conduct mechanoelectrical conversion via controllable distance of electromagnetic interaction during cyclic stretching–releasing process. To investigate the mechanoelectrical conversing mechanism, an equivalent Maxwell's numerical simulation is combined with experimental results, exploring different experimental parameters. Furthermore, diverse programmed patterning of GLMAs and structure designs are utilized to tune electrical performance. It is believed that the magnetic/electrical synergistic design principle will create a new avenue for liquid metals as functional material in the development of wearable electronics with large strains.

Magnetically Activated Electroactive Microenvironments for Skeletal Muscle Tissue Regeneration

This work reports on magnetoelectric biomaterials suitable for effective proliferation and differentiation of myoblast in a biomimetic microenvironment providing the electromechanical stimuli associated with this tissue in the human body. Magnetoelectric films are obtained by solvent casting through the combination of a piezoelectric polymer, poly(vinylidene fluoride-trifluoro-ethylene), and magnetostrictive particles (CoFe2O4). The nonpoled and poled (with negative and positive surface charge) magnetoelectric composites are used to investigate their influence on C2C12 myoblast adhesion, proliferation, and differentiation. It is demonstrated that the proliferation and differentiation of the cells are enhanced by the application of mechanical and/or electrical stimulation, with higher values of maturation index under mechanoelectrical stimuli. These results show that magnetoelectric cell stimulation is a full potential approach for skeletal muscle tissue engineering applications.