Magnetoelectric Heterostructures Research Articles

Arbitrary low-frequency power-splitting strategy in ferrite/piezoelectric magnetoelectric heterostructures: theory and experimental validation

Exploring low-frequency (LF) arbitrary power-splitting technologies to address the independent excitation issues of LF/VLF mechanical antennas (MA) with random distributions is challenging due to unidentified device construction and operation mechanism. In light of this, a device construction strategy for three-port magnetoelectric (ME) arbitrary power splitter in composite of ferrite/piezoelectric heterostructure, as well as theoretical model was developed. To validate the feasibility and effectiveness of the strategy, three size-tailored ME samples with length ratio of split PZT segments in 1:1, 2:1, and 3:2 were modeled, fabricated and comparatively characterized. Experimental results show that the achievable maximum power conversion efficiencies (PE) reach 52%, 71%, and 59% for three tailored ME samples, respectively, and as expected the power-splitting ratios are directly proportional to the square ratio of ME voltage coefficient (MEVC) from each port of the tailored ME samples, which are in coincidence with theory under desired operation stability and favorable experiment repeatability evaluated by uncertainties of 0.25854 V cm−1 Oe−1 and 0.32979 V cm−1 Oe−1 for each port. Therefore, a prediction of evolutionary tendency for arbitrary power splitter realization was expanded in view of our experimental observations, and a great flexibility for device future design and further optimization was also provided. Therefore, the presented LF power-splitting strategy paves the ways for arbitrary power splitter realization and enriches the multi-functional ME power electronics families, as well as enables potential applications for efficient excitations of MAs in high-permeable military underwater and civilian emergency rescue distribution long-wave communication system for practical scenarios of submarine, underground railways, tunnels and collapsed residential buildings.

Photo-strain induced magnetoresistance modulation in magnetoelectric heterostructure-based devices

The electric-field control of magnetic dynamics and magnetization in magnetoelectric (ME) heterostructures holds promise for energy-efficient beyond-CMOS devices. However, such techniques entail a high-saturation operational electric field near the device breakdown voltage and introduce complexity due to the requirement for electrical contacts. This study circumvents this issue by light-induced magnetoresistance (MR) modulation in a Ni/PMN-PT ME heterostructure driven by photo-strain-induced internal electric field. Reduced MR, especially in the perpendicular mode, is observed, signifying a localized reduction in the external magnetic field required for magnetization alignment, as elucidated by Langevin function analysis. The proposed method could facilitate better integration and scalability of ME-based spintronic devices, paving the way for low-power beyond-CMOS technologies.

Ultralow Electric Current-Assisted Magnetization Switching due to Thermally Engineered Magnetic Anisotropy.

Control of magnetic anisotropy in thin films with perpendicular magnetic anisotropy is of paramount importance for the development of spintronics with ultralow-energy consumption and high density. Traditional magnetoelectric heterostructures utilized the synergistic effect of piezoelectricity and magnetostriction to realize the electric field control of magnetic anisotropy, resulting in additional fabrication and modulation processes and a complicated device architecture. Here, we have systematically investigated the electric current tuning of the magnetic properties of the metallic NiCo2O4 film with intrinsic perpendicular magnetic anisotropy. Ferrimagnetic-to-paramagnetic phase transition has been induced through Joule heating, resulting in a rapid decrease of both magnetic coercivity and moment. An ultralow current density of 2.5 × 104 A/cm2, which is 2 to 3 orders magnitude lower than that of conventional spin transfer torque devices, has been verified to be effective for the control of the magnetic anisotropy of NiCo2O4. Successful triggering of magnetic switching has been realized through the application of a current pulse. These findings provide new perspectives toward the electric control of magnetic anisotropy and design of spintronics with an ultralow driving current density.

Ferroelectrically controlled electromagnetic and transport properties of VN2H2/Al2O3 van der Waals multiferroic heterostructures.

The vertical integration of a ferromagnetic monolayer and a ferroelectric monolayer into van der Waals heterostructures offers a promising route to achieve two-dimensional multiferroic semiconductors owing to the lack of intrinsic single-phase multiferroic materials in nature. In this study, we propose a VN2H2/Al2O3 van der Waals magnetoelectric multiferroic heterostructure and investigate its electronic, magnetic, and transport properties using density functional theory combined with the Boltzmann transport theory. The VN2H2 monolayer is a room-temperature ferromagnetic semiconductor with a band gap of 0.24 eV and a Curie temperature of 411 K, while the Al2O3 monolayer is a ferroelectric semiconductor with a polarization value of 0.11 C m-2. In the VN2H2/Al2O3 van der Waals heterostructures, the conversion between the metal and the semiconductor can be controlled by altering the polarization of the Al2O3 layer. The VN2H2/Al2O3 van der Waals heterostructure retains room-temperature ferromagnetism, and the reverse of polarization is accompanied with a change in the direction of the easy magnetization axis. In addition, electrostatic doping can significantly improve the conductivity of the downward polarization state and transform the upward polarization state from a metal to a half-metal, achieving 100% spin polarization. Our results thus pave the way for achieving highly tunable electromagnetic and transport properties in van der Waals magnetoelectric heterostructures, which have potential applications in next-generation low-power logic and memory devices.

Enhanced Proliferation and Differentiation of Human Osteoblasts by Remotely Controlled Magnetic-Field-Induced Electric Stimulation Using Flexible Substrates.

With the progressive aging of the population, bone fractures are an increasing major health concern. Diverse strategies are being studied to reduce the recovery times using nonaggressive treatments. Electrical stimulation (either endogenous or externally applied electric pulses) has been found to be effective in accelerating bone cell proliferation and differentiation. However, the direct insertion of electrodes into tissues can cause undesirable inflammation or infection reactions. As an alternative, magnetoelectric heterostructures (wherein magnetic fields are applied to induce electric polarization) could be used to achieve electric stimulation without the need for implanted electrodes. Here, we develop a magnetoelectric platform based on flexible kapton/FeGa/P(VDF-TrFE) (flexible substrate/magnetostrictive layer/ferroelectric layer) heterostructures for remote magnetic-field-induced electric field stimulation of human osteoblast cells. We show that the use of flexible supports overcomes the clamping effects that typically occur when analogous magnetoelectric structures are grown onto rigid substrates (which preclude strain transfer from the magnetostrictive to the ferroelectric layers). The study of the diverse proliferation and differentiation markers evidence that in all the stages of bone formation (cell proliferation, extracellular matrix maturation, and mineralization), the electrical stimulation of the cells results in a remarkably better performance. The results pave the way for novel strategies for remote cell stimulation based on flexible platforms not only in bone regeneration but also in many other applications where electrical cell stimulation may be beneficial (e.g., neurological diseases or skin regeneration).

Twisted Integration of Complex Oxide Magnetoelectric Heterostructures via Water-Etching and Transfer Process

HighlightsThe (001)-oriented ferromagnetic La0.67Sr0.33MnO3 films are stuck onto the (011)-oriented ferroelectric single-crystal 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate with 0° and 45° twist angle.By applying a 7.2 kV cm−1 electric field, the coexistence of uniaxial and fourfold in-plane magnetic anisotropy is observed in 45° Sample, while a typical uniaxial anisotropy is found in 0° Sample.Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering. In recent years, lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations. Moreover, twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures. A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process, which could provide some insight in to the physical phenomena. In this work, the La0.67Sr0.33MnO3 (001)/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (011) (LSMO/PMN-PT) heterostructures with 45º and 0º twist angles were assembled via water-etching and transfer process. The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO < 110 >. A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO [110] easy axis is observed for the 45° Sample by applying a 7.2 kV cm−1 electrical field, significantly different from a uniaxial anisotropy with LSMO [100] easy axis for the 0° Sample. The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45° twist angle causes different lattice distortion of LSMO, thereby enhancing both the fourfold and uniaxial anisotropy. This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures.

Effect of Hf alloying on magnetic, structural, and magnetostrictive properties in FeCo films for magnetoelectric heterostructure devices

Materials with high magnetoelectric coupling are attractive for use in engineered multiferroic heterostructures with applications such as ultra-low power magnetic sensors, parametric inductors, and non-volatile random-access memory devices. Iron–cobalt alloys exhibit both high magnetostriction and high saturation magnetization that are required for achieving significantly higher magnetoelectric coupling. We report on sputter-deposited (Fe0.5Co0.5)1−xHfx (x = 0 – 0.14) alloy thin films and the beneficial influence of Hafnium alloying on the magnetic and magnetostrictive properties. We found that co-sputtering Hf results in the realization of the peening mechanism that drives film stress from highly tensile to slightly compressive. Scanning electron microscopy and x-ray diffraction along with vibrating sample magnetometry show reduction in coercivity with Hf alloying that is correlated with reduced grain size and low film stress. We demonstrate a crossover from tensile to compressive stress at x ∼ 0.09 while maintaining a high magnetostriction of 50 ppm and a low coercive field of 1.1 Oe. These characteristics appear to be related to the amorphous nature of the film at higher Hf alloying.

Functionality in frequency tuning of magnetoelectric heterostructure integrated highly flexible bulk acoustic wave resonator

Functional flexible piezo-resonators are of vital interest for designing micro-electrometrical system (MEMS) based high-frequency wearable devices. The magnetoelectric (ME) heterostructure comprising highly magnetostrictive Ni–Mn–In and piezoelectric AlN films was fabricated over flexible substrates to develop the bulk acoustic wave (BAW) resonator. The BAW resonators fabricated over Ni and Kapton substrates show the fundamental resonance at ∼5.535 and 5.400 GHz, respectively. The comparative study of frequency tuning for both resonators has been executed in the presence of a dc magnetic field. A larger frequency shift (ΔfR) of ∼540 MHz was detected at 1200 Oe for a device fabricated over Ni with a sensitivity of ∼5.4 Hz/nT. However, it is 360 MHz in the case of Kapton, with a sensitivity of ∼3.0 Hz/nT. Moreover, the BAW resonator over the magnetostrictive Ni substrate shows a higher tunability of ∼11.4% compared to ∼8.5% for the resonator fabricated over non-magnetostrictive Kapton. The equivalent modified Butterworth–Van Dyke circuit parameters have been extracted by fitting the experimental data with and without an external magnetic field using advanced design system. The effect of an external magnetic field has been thoroughly investigated on device parameters, such as electromechanical coupling coefficient (K2), acoustic velocity, quality factor (Q), and figure of merit. The anisotropic functionality of the fabricated resonator has been studied by measuring the tunability of the resonator in parallel and perpendicular magnetic fields. The present study motivates the incorporation of flexible magnetostrictive substrates for futuristic multifunctional MEMS magnetic field sensor applications.

Angular magnetic field dependence of a doubly clamped magnetoelectric resonator

Angular dependence of magnetic field response of fully suspended resonant microelectromechanical double-clamped magnetoelectric beams was investigated as the basis for a vector magnetometer utilizing the magnetically induced change in fundamental resonance frequency. Strain-coupled magnetostrictive iron cobalt (FeCo) and piezoelectric aluminum nitride layers together constitute a magnetoelectric heterostructure with a high magnetic field sensitivity of 70 Hz/mT along the beam axis and a transfer function of 47 V/T at 10 Hz. The fundamental frequency shift to an external magnetic field is found to be strongly anisotropic with a relative variation of more than 3% between perpendicular and parallel field orientations with respect to the long axis of the beam at a field of 100 mT. This design can form the basis for an on-chip high sensitivity vector magnetometer operating with ultra-low power when multiplexed with two or more resonators.

Flexible magnetoelectric sensor and nonvolatile memory based on magnetization-graded Ni/FSMA/PMN-PT multiferroic heterostructure

Flexible multiferroic heterostructures are promising to unveil technological developments in wearable magnetic field sensing, nonvolatile memory, soft robotics, and portable energy harvesters. Here, we report an enhanced and a zero-biased magnetoelectric (ME) effect in flexible, cost-effective, and room temperature sensitive Ni/FSMA/PMN-PT magnetization-graded ME heterostructure. Flexible Ni foil with −q (piezomagnetic coefficient) and the ferromagnetic shape memory alloy (FSMA; Ni-Mn-In) layer with +q offers the desired q-grading. The temperature-dependent dielectric behavior shows an anomaly in the martensite transformation regime of the FSMA layer. The Ni/FSMA/PMN-PT ME heterostructure exhibits noteworthy ME output of ∼3.7 V/cm Oe, significantly higher than Ni/PMN-PT (∼1 V/cm Oe). The q-grading-induced bending moment impedes the asymmetry-related flexural strain and strengthens the ME interaction. The zero-bias ME output of ∼0.4 V/cm Oe is ascribed to the interaction between q-grading-induced transverse magnetization and AC magnetic field. Ni/Ni-Mn-In/PMN-PT ME heterostructure displays excellent magnetic field sensing parameters: correlation coefficient, sensitivity, inaccuracy, and hysteresis of 0.99916, ∼0.74 mV/Oe, 1.5% full-scale output (FSO), and 1.8% FSO, respectively. The reversible and repeatable nonvolatile switching of the ME coefficient obtained with positive and negative electric fields is useful for next-generation memory devices. The flexible ME heterostructure shows no degradation in performance up to 1500 bending cycles. Such Ni/FSMA/PMN-PT based ME heterostructures are propitious for multifunctional flexible magnetic field sensors and nonvolatile memory applications.

Electric and magnetic tuning of Gilbert damping constant in LSMO/PMN-PT(011) heterostructure

Electric field control of magnetodynamics in magnetoelectric (ME) heterostructures has been the subject of recent interest due to its fundamental complexity and promising applications in room temperature (RT) devices. The present work focuses on the tuning of magnetodynamic parameters of epitaxially grown ferromagnetic (FM) La0.7Sr0.3MnO3 (LSMO) on a ferro(piezo)electric (FE) Pb(Mg0.33Nb0.67)O3-PbTiO3 (PMN-PT) single crystal substrate. The uniaxial magnetic anisotropy of LSMO on PMN-PT confirms the ME coupling at the FM/FE heterointerface. The magnitude of the Gilbert damping constant (α) of this uniaxial LSMO film measured along the hard magnetic axis is significantly small compared to the easy axis. Furthermore, a marked decrease in the α values of LSMO at positive and negative electrical remanence of PMN-PT is observed, which is interpreted in the framework of strain induced spin dependent electronic structure. The present results clearly encourage the prospects of electric field controlled magnetodynamics, thereby realising the RT spin-wave based device applications with ultra-low power consumption.

A magnetoelectric heterostructure employing a magnetic levitation mechanism for harvesting low-frequency vibration energy

A magnetoelectric (ME) heterostructure using shear-mode ME transducers to extract ambient low-frequency vibration energy is proposed. The demand for the traditional mechanical spring is eliminated by utilizing a magnetic levitation mechanism. When the suspending magnet moves relative to the ME transducers, the piezoelectric plates deform in shear mode owing to the magnetostriction of the magnetostrictive plates, and large shear piezoelectric effect is induced. Consequently, larger voltages can be produced by the presented device. The kinetic equation of the energy harvesting system is derived and solved, and the maximum output power is obtained based on the vibration rule and the variation of the sensed magnetic field. The feasibility of the heterostructure is experimentally verified. The maximum load power increases with acceleration. A maximum output power of 1.46mW is generated across a 1.25MΩ resistive load at the acceleration of 0.7g. The generated energy of the heterostructure is sufficient to drive a low-power electronic device. Improvements are feasible, which allow an obvious increase of the maximum output powers by employing a Halbach array with a particular arrangement of the magnets.

Flexible magnetoelectric complex oxide heterostructures on muscovite for proximity sensor

In modern technology, recent advances in multi-functional devices are rapidly developed for the diverse demands of human beings. Meanwhile, durability and adaptability to extreme environmental conditions are also required. In this study, a flexible magnetoelectric (ME) heterostructure based on CoFe2O4/Pb(Zr,Ti)O3 composite thin film on muscovite is presented, with two geometries of the constituents, namely laminar heterostructure, and vertical nanostructure, adopted for the comparison. On the other hand, credited to the mechanical flexibility of muscovite, the impact of flexibility on ME properties is also discussed with a series of bending tests. Moreover, the ME response sustains for 10,000 times bending without significant decrease, validating the mechanical durability of this heterostructure on muscovite. With these advantages, a flexible proximity sensor based on this heterostructure is demonstrated for motion detection. It is expected to offer a pathway for creating the next-generational flexible devices, showing potential for future practical application.

Magnetoelectric MEMS Magnetic Field Sensor Based on a Laminated Heterostructure of Bidomain Lithium Niobate and Metglas.

Non-contact mapping of magnetic fields produced by the human heart muscle requires the application of arrays of miniature and highly sensitive magnetic field sensors. In this article, we describe a MEMS technology of laminated magnetoelectric heterostructures comprising a thin piezoelectric lithium niobate single crystal and a film of magnetostrictive metglas. In the former, a ferroelectric bidomain structure is created using a technique developed by the authors. A cantilever is formed by microblasting inside the lithium niobate crystal. Metglas layers are deposited by magnetron sputtering. The quality of the metglas layers was assessed by XPS depth profiling and TEM. Detailed measurements of the magnetoelectric effect in the quasistatic and dynamic modes were performed. The magnetoelectric coefficient |α32| reaches a value of 492 V/(cm·Oe) at bending resonance. The quality factor of the structure was Q = 520. The average phase amounted to 93.4° ± 2.7° for the magnetic field amplitude ranging from 12 to 100 pT. An AC magnetic field detection limit of 12 pT at a resonance frequency of 3065 Hz was achieved which exceeds by a factor of 5 the best value for magnetoelectric MEMS lead-free composites reported in the literature. The noise level of the magnetoelectric signal was 0.47 µV/Hz1/2. Ways to improve the sensitivity of the developed sensors to the magnetic field for biomedical applications are indicated.

Магнитоэлектрический гиратор на основе трехслойных симметричных структур: теория и эксперимент

The work is devoted theoretical and experimental studies of a magnetoelectric gyrator, consisting of an inductor coil, inside which there is a magnetoelectric heterostructure, which is a mechanically connected piezoelectric layer and two magnetic layers. Using the system of equations of elasto- and electrodynamics for the piezoelectric and magnetostrictive phases, expressions are obtained for the current/voltage conversion coefficient of the gyrator in terms of the phase parameters of the heterostructure. An experimental sample of a gyrator based on the Metglas/PZT/Metglas heterostructure was fabricated. Theoretically calculated and experimentally studied the frequency and load characteristics of the gyrator. It is shown that theoretical calculations are in good agreement with experimental data. Recommendations for the creation of gyrators with the highest current/voltage conversion efficiency are presented.

Low-Frequency Dual-Driven Magnetoelectric Antennas With Enhanced Transmission Efficiency and Broad Bandwidth

Low frequency (LF) dual-driven magnetoelectric (i.e., DDME) antennas are proposed, which include a pair of self-biased magnetoelectric (ME) heterostructures (i.e., Ni/Metglas/ [Pb(Zr,Ti)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> /Metglas/Ni) wrapped with small coils. For the DDME transmitter, the [Pb(Zr,Ti)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> layers are designed as a piezoelectric transformer. This enhances the transmitted magnetic field significantly due to the dual-driven mode: the generated magnetic field of transmitting coils driven by the transformer at the magneto-mechanical resonance (MMR) and magnetization oscillation of magnetostrictive layer driven by the mechanical stress of inverse piezoelectric effect. Meanwhile, the DDME receiver consists of a self-biased ME heterostructure wrapped with search coils, whose signal-to-noise ratio (SNR) is improved due to the synergistically induced voltage of Faraday law's induction and ME effects. The nonmonotonic inductance of search coils near MMR broadens the bandwidth (1904 kHz) due to the LC resonances at multiple frequencies. The letter indicates that the DDME antenna achieves a communication distance of 11 m with power consumption of 212.7 mW, whose operation distance and channel capacity (12.54 kbit/s) are 1.69 times and 10.62 times larger than that of ME antenna (i.e., Ni/Metglas/[Pb(Zr,Ti)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> /Metglas/Ni). The communication distance can be further increased to 170 m with a larger DDME antenna. Furthermore, the DDME antenna can realize more robust ASK modulation compared to ME antenna.

Deterministic domain wall rotation in a strain mediated FeGaB/PMN-PT asymmetrical ring structure for manipulating trapped magnetic nanoparticles in a fluidic environment.

The manipulation of domain walls (DWs) in strain-mediated magnetoelectric (ME) heterostructures has attracted much attention recently, with potential applications in precise and location-specific manipulation of magnetic nanoparticles (MNPs). However, the manipulation ability in these structures is restricted to magnetostrictive circular ring structures only, where the required onion state is metastable, less thermally stable, and cannot be obtained easily. This work investigates the highly shape anisotropic FeGaB magnetostrictive elliptical ring structures of different aspect ratios and trackwidths on the PMN-PT piezoelectric substrate to manipulate fluid-borne MNPs using active control of DWs. The proposed model utilizes the attribute that the required onion state in a magnetostrictive elliptical ring is thermally stable and easily obtained compared to magnetostrictive circular ring structures. By varying the trackwidth of elliptical rings, nucleated DWs are rotated at different angles to capture and transport fluid-borne MNPs. Up to a critical trackwidth, DW rotation is predicted by dominant stress anisotropy energy that leads the rotation of DWs and attached MNPs toward the dominant tensile strain direction of PMN-PT with reversibility. Increasing the trackwidth beyond the critical trackwidth caused a complete 90° rotation of DWs and attached MNPs without reversibility and is given by dominant shape anisotropy energy. The fundamental relationship of capture probability with the size and velocity of injected MNPs is also demonstrated. The nucleation and rotation of DWs are predicated using the coupled elastodynamic and electrostatic Finite Difference Method (FDM) micromagnetic model. Dynamics of MNP capture and rotation are envisaged using an analytical model.

Strain and charge contributions to the magnetoelectric coupling in Fe3O4/PMN-PT artificial multiferroic heterostructures

The quest to realize new kinds of data storage devices has motivated recent studies in the field of magnetoelectric heterostructures. One of the most commonly investigated systems is Fe3O4/[Pb(MgNbO3]0.7–[PbTiO3]0.3 (PMN-PT), however, the interplay between different coupling mechanisms is not yet well understood. To disentangle the role of strain and polarisation influence in Fe3O4/PMN-PT, we report on magnetoelectric coupling measurements for different orientations of the applied magnetic field and for two different substrate cuts, PMN-PT(001) and PMN-PT(011). For Fe3O4/PMN-PT(011), having the sample aligned such that the magnetic field is parallel to the [01] easy axis leads to a remanent increase of the magnetisation for each electric field cycle. On the other hand, for the magnetic field along the [100] hard axis, the magnetisation follows a butterfly-like loop characteristic of strain coupling imparted by the substrate. For Fe3O4/PMN-PT(001), the magnetoelectric effect is a superposition of the observed behaviour of both in-plane directions in Fe3O4/PMN-PT(011). The magnetisation shows an initial remanent increase followed by a butterfly like loop. Polarised neutron reflectometry measurements on Fe3O4/PMN-PT(011) shows no difference between the behaviour at the interface and the bulk of the film and no decline of the interaction further away from the shared interface. Our results demonstrate the role of strain and polarisation on the magnetisation of the Fe3O4 layer and provide a clear step towards the design of future magnetoelectric systems.

Electric field tuning of ultrafast demagnetization in a magnetoelectric heterostructure

Voltage/electric-field control of ultrafast magnetization dynamics in magnetoelectrics provides a novel avenue for electronic tuning with orders of magnitude less power consumption, improved tuning response time, and more compact form factor, compared with conventional magnetic field control of magnetization dynamics. Magnetoelectrically tuned laser-driven magnetization dynamics has the potential to enable the next generation of optomagnetic devices from THz communication to optical magnetic recording. In this study, we fabricated a magnetoelectric heterostructure, specifically ferromagnetic ${({\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19})}_{88}{\mathrm{B}}_{12}$ (FeGaB) thin film deposited on a $\mathrm{Pb}({\mathrm{Mg}}_{1/3}\phantom{\rule{0.16em}{0ex}}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{PbTi}{\mathrm{O}}_{3}$ ferroelectric substrate, to explore the electric field tuning of ultrafast demagnetization and to understand how magnetic anisotropy changes postdemagnetization. We characterized the magnetoelectric coupling of our heterostructure to demonstrate the static and dynamic magnetization tunability with an applied electric field. We utilized the time-resolved magneto-optic Kerr effect to understand the ultrafast demagnetization process under different applied electric fields and magnetic fields. The typically observed strain-induced magnetic easy-axis rotation in a ferromagnetic/ferroelectric heterostructure was also observed to tune the ultrafast demagnetization of FeGaB in our experiment. Additionally, we found that the magnetization rotation can be achieved with a lower electric field compared with static tuning without laser heating. Furthermore, we observed the hysteresis loops postultrafast demagnetization and found that the magnetoelectric heterostructure exhibits a mixture of volatile and nonvolatile behaviors. These findings shed light on the potential of our magnetoelectric heterostructure for ultrafast optomagnetic devices and electric field tuning of spintronic THz emitters.

A Shear-Mode Magnetoelectric Heterostructure with Enhanced Magnetoelectric Response for Stray Power-Frequency Magnetic Field Energy Harvesting.

This paper devises a magnetoelectric (ME) heterostructure to harvest ambient stray power-frequency (50 Hz or 60 Hz) magnetic field energy. The device explores the shear piezoelectric effect of the PZT-5A plates and the magnetostrictive activity of the Terfenol-D plates. The utilization of the high-permeability films helps to enhance the magnetoelectric response to the applied alternating magnetic field. A theoretical model is developed based on the piezomagnetic and piezoelectric constitutive equations as well as the boundary conditions. The ME response of the device is characterized theoretically and experimentally. The measured ME voltage coefficient attains 165.2 mV/Oe at the frequency of 50 Hz, which shows a good agreement with the theoretical result. The feasibility for extracting energy from the 50 Hz magnetic field is validated. Under an external alternating magnetic field of 30 Oe, a maximum power of 8.69 μW is generated across an optimal load resistance of 693 kΩ. Improvements of the ME heterostructure are practicable, which allows an enhancement of the ME voltage coefficient and the maximum power by optimizing the structural parameters and utilizing PMN-PT with a higher shear-mode piezoelectric voltage coefficient (g15).