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A 400 MHz magnetoelectric (ME) Lamb wave antenna design to function in the medical implant communication service band is proposed. The antenna employs a heterostructure of piezoelectric and magnetostrictive membranes to acoustically excite standing shear bulk wave and radiate as a magnetic dipole. Multiphysics finite element analysis simulations are performed for transmission and reception modes. In these simulations, three aspects are investigated: piezoelectricity, micromagnetic precession, and magnetic dipole radiation. An experimental demonstration of the antenna is also conducted and shows mechanical resonance with a Q-factor of 500 and ME coupling. These results indicate that the design can be operated in zero-order antisymmetric (A0) mode as a tunable oscillator or sensor. This ME approach provides a solution to the miniaturization problem of traditional current-based implantable antennas.

Bayesian optimization is a well-developed machine learning field for black box function optimization. In Bayesian optimization a surrogate predictive model, here a Gaussian process, is used to approximate the black box function. The estimated mean and uncertainty of the surrogate model are paired with an acquisition function to decide where to sample next. In this study we applied this technique to known ferromagnetic thin film materials such as ferromagnetic (Fe100-y Gay)1-xBx (x=0 to 21 & y=9 to 17) and (Fe100-y Gay)1-xCx (x=1 to 26 and y=2 to 18) to demonstrate optimization of structure-property relationships, specifically the dopant concentration or stoichiometry effect on magnetostriction and ferromagnetic resonance linewidth. Our results demonstrated that Bayesian optimization can be deployed to optimize structure-property relationships in FeGaB and FeGaC thin films. We have shown through simulation that using Bayesian optimization methods to guide experiments reduced the number of samples required to statistically determine the maximum or minimum by 50 % compared to traditional methods. Our results suggest that Bayesian optimization can be used to save time and resources to optimize ferromagnetic films. This method is transferrable to other ferromagnetic material structure-property relationships, providing an accessible implementation of machine learning to magnetic materials development.

Over the past three decades, we have seen significant advances in the field of wireless implantable medical devices (IMDs) that can interact with the nervous system. To further improve the stability, safety, and distribution of these interfaces, a new class of implantable devices is being developed: single-channel, sub-mm scale, and wireless microelectronic devices. In this research, we describe a new and simple technique for fabricating and assembling a sub-mm, wirelessly powered stimulating implant. The implant consists of an ASIC measuring 900 × 450 × 80 µm3, two PEDOT-coated microelectrodes, an SMD inductor, and a SU-8 coating. The microelectrodes and SMD are directly mounted onto the ASIC. The ultra-small device is powered using electromagnetic (EM) waves in the near-field using a two-coil inductive link and demonstrates a maximum achievable power transfer efficiency (PTE) of 0.17% in the air with a coil separation of 0.5 cm. In vivo experiments conducted on an anesthetized rat verified the efficiency of stimulation.

A novel acoustic noise dosimeter is presented in this letter to investigate and measure the sound noise level that damages human hearing. A miniaturized magnetoelectric (ME) antenna is utilized to sense the sound noise level through the nonlinear antenna modulation around the operating acoustic resonance frequency of 63.6 MHz. Applied noise level of 102 dBA at two different 300 kHz and 1 kHz frequencies results in 33.8 dB and 28.7 dB signal to noise ratio. In addition, the fabricated antenna provides a high frequency of resonance of 2.49 GHz for energy harvesting and communications.

Strongly correlated oxides with a broken symmetry could exhibit various phase transitions, such as superconductivity, magnetism and ferroelectricity. Construction of superlattices using these materials is effective to design crystal symmetries at atomic scale for emergent orderings and phases. Here, antiferromagnetic Ruddlesden-Popper Sr2IrO4 and perovskite paraelectric (ferroelectric) SrTiO3 (BaTiO3) are selected to epitaxially fabricate superlattices for symmetry engineering. An emergent magnetoelectric phase transition is achieved in Sr2IrO4/SrTiO3 superlattices with artificially designed ferroelectricity, where an observable interfacial Dzyaloshinskii-Moriya interaction driven by non-equivalent interface is considered as the microscopic origin. By further increasing the polarization namely interfacial Dzyaloshinskii-Moriya interaction via replacing SrTiO3 with BaTiO3, the transition temperature can be enhanced from 46 K to 203 K, accompanying a pronounced magnetoelectric coefficient of ~495 mV/cm·Oe. This interfacial engineering of Dzyaloshinskii-Moriya interaction provides a strategy to design quantum phases and orderings in correlated electron systems., A controllable magnetoelectric phase based on symmetry engineering is challenge in natural bulk crystals. Here, via engineering of interfacial Dzyaloshinskii-Moriya interaction, the authors design a magnetoelectric phase transition in oxide superlattices of correlated electron systems.

Ultra-compact wireless implantable medical devices are in great demand for healthcare applications, in particular for neural recording and stimulation. Current implantable technologies based on miniaturized micro-coils suffer from low wireless power transfer efficiency (PTE) and are not always compliant with the specific absorption rate imposed by the Federal Communications Commission. Moreover, current implantable devices are reliant on differential recording of voltage or current across space and require direct contact between electrode and tissue. Here, we show an ultra-compact dual-band smart nanoelectromechanical systems magnetoelectric (ME) antenna with a size of 250 × 174 µm2 that can efficiently perform wireless energy harvesting and sense ultra-small magnetic fields. The proposed ME antenna has a wireless PTE 1–2 orders of magnitude higher than any other reported miniaturized micro-coil, allowing the wireless IMDs to be compliant with the SAR limit. Furthermore, the antenna’s magnetic field detectivity of 300–500 pT allows the IMDs to record neural magnetic fields., Wireless implantable medical devices (IMDs) are hamstrung by both size and efficiency required for wireless power transfer. Here, Zaeimbashi et al. present a magnetoelectric nano-electromechanical systems that can harvest energy and sense weak magnetic fields like those arising from neural activity.

In order to advance the potential of thick on-chip hard magnets for the micro-electro-mechanical system (MEMS), we investigate a new silicon molding technique to fabricate dry-packed NdFeB magnets, including a silicon compression tool, which enables the pressing step during silicon-compatible processing. This process delivers samples with a remanence of 0.42 T and an energy product of 38 kJ/m3. Further studies of metal molding show that, for wax-bonding powder-based NdFeB magnets, the optimum fabrication condition is 300 °C and 425 MPa, giving a remanence of 0.54 T and an energy product of 61.7 kJ/m3.

We report the first study of diverse ferromagnetic thin films via acoustically driven ferromagnetic resonance (ADFMR). Angle- and field-dependent ADFMR was performed at room temperature on thin films of FeCo, FeCoGd, FeGaB, and FeCoSiB, which take the place of the ferromagnetic Ni film traditionally used in these experiments, with a few exceptions. Surface acoustic wave (SAW) devices are operated at three harmonics in the 0.8–2 GHz frequency range. Each magnetic material has a unique ADFMR signature: FeCo shows a standard 4-lobe pattern with a broad $\sim 100$ mT linewidth; FeCoGd breaks odd symmetry and reveals an additional low-field lobe; and FeGaB and FeCoSiB show extreme asymmetry and narrow linewidths. In FeCoSiB, we observe nonreciprocal SAW propagation. We also perform direct comparison of ADFMR and standard ferromagnetic resonance (FMR) on the same devices, revealing that ADFMR absorption is measurable even when FMR signals are extremely weak, and magnetic anisotropy does not fully explain asymmetry observed in ADFMR. These results demonstrate that strain-driven magnetization dynamics is a rich field; the effects can be observed in a variety of materials with unexpected behavior, motivating further work in the field.

The nonreciprocal bandpass filter has been achieved by utilizing the nonreciprocity characteristics of the magnetostatic surface wave (MSSW) in planar ferrite slabs. In this article, the dispersion relation, impedance, and attenuation of MSSW between the pure and metallized ferrite slabs have been analyzed and compared. Theoretical analysis indicates that the ferrite slab metallized by a thin conductive layer would introduce significant attenuation on the metallized interface, which is MSSW propagating on the isolated direction, while MSSW on the other surface is barely affected. Therefore, nonreciprocal bandpass filter with enhanced isolation can be achieved with metallized ferrite slab. Simulated S-parameters show that a notch in the isolating direction can be obtained at the passing band of the transmitting direction. Experimental results show that the nonreciprocal filter with metallized yttrium iron garnet (YIG) slab (by depositing 100- $\mathbf {nm}$ copper film) exhibits more than 10-dB higher isolation than that with pure YIG slab, while the center frequency, insertion loss, and 3-dB bandwidth maintain almost the same. The center frequency of the filter with metallized YIG slab can be tuned from 7.26 to 8.38 GHz with insertion loss of less than 3 dB, and in-band isolation of more than 30 dB as the dc bias magnetic field is increased from 1.8 to 2.3 kOe. Besides, the nonreciprocal filter has ultra-wide out-band suppression since it utilizes the narrow frequency band of MSSW. The −10-dB out-band rejection exceeds 36 GHz in the upper band and 1 MHz in the lower band.

In this paper, we report all-optical manipulation of magnetization in ferromagnetic Co/Pt thin films enhanced by plasmonic resonances. By annealing a thin Au layer, we fabricate large-area Au nanoislands on top of the Co/Pt magnetic thin films, which show plasmonic resonances around the wavelength of 606 nm. Using a customized magneto-optical Kerr effect setup, we experimentally observe an 18.5% decrease in the minimum laser power required to manipulate the magnetization, comparing the on- and off-resonance conditions. The results are in very good agreement with numerical simulations. Our research findings demonstrate the possibility to achieve an all-optical magnetic recording with low energy consumption, low cost, and high areal density by integrating plasmonic nanostructures with magnetic media.

A great challenge in power/RF electronics has been achieving integrated magnetic inductors with high quality factor ( $Q$ -factor) and high inductance density at gigahertz frequencies. In this article, integrated solenoid magnetoelectric inductors based on FeGaB/Al2O3 multilayer as the magnetic core are designed to operate at high gigahertz frequencies, high $Q$ -factor, and inductance tunability. A high self-resonant frequency of >3 GHz with a flat inductance of 1.4 nH and a peak $Q$ -factor of ~32.7 has been achieved within a wide operating frequency ranging from 0.3 to 3 GHz with magnetic annealing treatment to enhance the inductance density and $Q$ -factor. Two different inductance-tuning methods are tested. For magnetic field tuning, an external magnetic field from 0 to 500 Oe is applied to achieve an inductance tunability $\Delta {\mathbf {L}/\mathbf {L}} _{\mathbf {min}}$ of ~69.2%. Voltage tuning is also tested based on the magnetoelectric coupling between FeGaB/Al2O3 multilayer and ferroelectric slab achieving a maximum tunability of 191% with a flat inductance within the operating frequency. Such a high $Q$ -factor and high inductance density together with giant electrical tunability will greatly improve the integration level and performance of tunable radio frequency integrated circuits while reducing their power consumption and cost.

A novel very low frequency (VLF) communication system using one pair of magnetoelectric (ME) antennas has been proposed. The ME antennas are strain-mediated acoustic resonators operating at their electromechanical resonance in the VLF band. The measured near-field radiation pattern reveals ME antennas are equivalent to dipole antennas. The magnetic field radiated by the ME transmitter has been predicted along with distance ranging from 1 mm to 100 km. The measured magnetic field distribution coincided well with the prediction, and the maximum communication distance of 120 m has been achieved. With 80 V driving voltage, the power consumption of the ME transmitter has been measured as 400 mW. Furthermore, the direct antenna modulation (DAM) has also been successfully demonstrated on the ME antennas.

Non-invasive stimulation of deep brain regions has been a major goal for neuroscience and neuromodulation in the past three decades. Transcranial magnetic stimulation (TMS), for instance, cannot target deep regions in the brain without activating the overlying tissues and has a poor spatial resolution. In this manuscript, we propose a new concept that relies on the temporal interference of two high-frequency magnetic fields generated by two electromagnetic solenoids. To illustrate the concept, custom solenoids were fabricated and optimized to generate temporal interfering electric fields for rodent brain stimulation. C-Fos expression was used to track neuronal activation. C-Fos expression was not present in regions impacted by only one high-frequency magnetic field indicating ineffective recruitment of neural activity in non-target regions. In contrast, regions impacted by two fields that interfere to create a low-frequency envelope display a strong increase in c-Fos expression. Therefore, this magnetic temporal interference solenoid-based system provides a framework to perform further stimulation studies that would investigate the advantages it could bring over conventional TMS systems.

Objective. Noninvasive focal stimulation of deep brain regions has been a major goal for neuroscience and neuromodulation in the past three decades. Transcranial magnetic stimulation (TMS), for instance, cannot target deep regions in the brain without activating the overlying tissues and has poor spatial resolution. In this manuscript, we propose a new concept that relies on the temporal interference (TI) of two high-frequency magnetic fields generated by two electromagnetic solenoids. Approach. To illustrate the concept, custom solenoids were fabricated and optimized to generate temporal interfering electric fields for rodent brain stimulation. C-Fos expression was used to track neuronal activation. Main result. C-Fos expression was not present in regions impacted by only one high-frequency magnetic field indicating ineffective recruitment of neural activity in non-target regions. In contrast, regions impacted by two fields that interfere to create a low-frequency envelope display a strong increase in c-Fos expression. Significance. Therefore, this magnetic temporal interference solenoid-based system provides a framework to perform further stimulation studies that would investigate the advantages it could bring over conventional TMS systems.

A low-noise amplifier (LNA) topology with tunable input matching and noise cancellation is introduced and described in this paper, which was designed and optimized to interface with a magnetoelectric (ME) antenna in a 0.35 µm MEMS-compatible CMOS process. Compared to conventional antennas, acoustically actuated ME antennas have significantly smaller area for ease of integration. The LNA was simulated with an ME antenna model that was constructed based on antenna measurements. Input matching at the LNA-antenna interface is controlled with a circuit that varies the effective impedance of the gate inductor using a control voltage. Tunability of 455 MHz around 2.4 GHz is achieved for the optimum S11 frequency with a control voltage range of 0.3 V to 1.2 V. The proposed LNA has a noise cancelling feedback loop that improves the noise figure by 4.1 dB. The post-layout simulation results of the LNA show a 1-dB compression point of −7.4 dBm with an S(21) of 17.8 dB.

A magnetoelectric antenna (ME) is a miniaturized device that exhibits the dual capability of energy harvesting and sensing in different frequency bands. In this paper, a behavioral circuit model for the ME antenna is presented to capture the radio frequency (RF) energy harvesting operation during circuit simulations. The ME antenna design of this work is under development for wireless communication with implantable devices, where one role of the antenna is to receive pulse-modulated power from a nearby transmitter. In this application, the proposed behavioral ME antenna model can be utilized during design optimizations of the energy harvesting circuits. The model has been assessed through simulations with an energy harvester design in 65nm CMOS technology. Measurements were performed to validate the results of the wireless power transfer link with an ME antenna having a 2.57 GHz resonance frequency connected to an energy harvester chip.

The possibility of tuning the magnetic properties of materials with voltage (converse magnetoelectricity) or generating electric voltage with magnetic fields (direct magnetoelectricity) has opened new avenues in a large variety of technological fields, ranging from information technologies to healthcare devices and including a great number of multifunctional integrated systems, such as mechanical antennas, magnetometers, and radio frequency (RF) tunable inductors, which have been realized due to the strong strain-mediated magnetoelectric (ME) coupling found in ME composites. The development of single-phase multiferroic materials (which exhibit simultaneous ferroelectric and ferromagnetic or antiferromagnetic orders), multiferroic heterostructures, as well as progress in other ME mechanisms, such as electrostatic surface charging or magneto-ionics (voltage-driven ion migration), have a large potential to boost energy efficiency in spintronics and magnetic actuators. This article focuses on existing ME materials and devices and reviews the state of the art in their performance. The most recent progress on different ME devices based on ME heterostructures is presented but with a larger emphasis on ME antennas and sensors due to the significant advances achieved in these applications. The rapid development of mechanically actuated ME antennas has been observed over the past several years, producing ME antennas that are miniaturized by 1-2 orders compared to conventional antenna size. Magnetic sensors based on simple ME composites are potentially promising alternatives to conventional magnetometers due to their very good detectivity (, The work of Patrick Hayes, Viktor Schell, Eckhard Quandt, and Jeffrey McCord was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) through the Collaborative Research Center CRC 1261 "Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics." The work of Pedro Martins was supported in part by the Fundacao para a Ciencia e Tecnologia (FCT) in the framework of the Strategic Funding under Grant UID/FIS/04650/2020 and under Project PTDC/BTMMAT/28237/2017 and Project PTDC/EMD-EMD/28159/2017, in part by the Fundacao para a Ciencia e Tecnologia (FCT) for the contract under the Stimulus of Scientific Employment, Individual Support-2017 Call, under Grant CEECIND/03975/2017, in part by the Spanish State Research Agency (AEI), in part by the European Regional Development Fund (ERFD) under Project PID2019-106099RB-C43/AEI/10.13039/501100011033, and in part by the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK, and PIBA (Grant PIBA-2018-06) Programs. The work of Marisa Medarde was supported in part by the Swiss National Science Foundation under Grant 200021-141334 and Grant 206021_139082, in part by the Swiss National Center of Competence in Research MARVEL (Computational Design and Discovery of Novel Materials) under Grant 1NF40_182892, in part by the European Community's 7th Framework Program under Grant 290605 (COFUND:PSI-FELLOW). The work of Senentxu Lanceros-Mendez was supported in part by the Fundacao para a Ciencia e Tecnologia (FCT) in the framework of the Strategic Funding under Grant UID/FIS/04650/2020 and under Project PTDC/BTM-MAT/28237/2017 and Project PTDC/EMD-EMD/28159/2017, in part by the Spanish State Research Agency (AEI), in part by the European Regional Development Fund (ERFD) under Project PID2019-106099RB-C43/AEI/10.13039/501100011033, and in part by the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK, and PIBA (Grant PIBA-2018-06) Programs. The work of Sebastiaan van Dijken was supported

Electrical stimulation via invasive microelectrodes is commonly used to treat a wide range of neurological and psychiatric conditions. Despite its remarkable success, the stimulation performance is not sustainable since the electrodes become encapsulated by gliosis due to foreign body reactions. Magnetic stimulation overcomes these limitations by eliminating the need for a metal-electrode contact. Here, we demonstrate a novel microfabricated solenoid inductor (80 µm × 40 µm) with a magnetic core that can activate neuronal tissue. The characterization and proof-of-concept of the device raise the possibility that micromagnetic stimulation solenoids that are small enough to be implanted within the brain may prove to be an effective alternative to existing electrode-based stimulation devices for chronic neural interfacing applications.

Van der Waals (vdW) layered GeTe-Sb 2 Te 3 superlattices (GST-SL) have attracted enormous attentions due to the ultralow power consumption for nonvolatile phase change memory. In this paper, effects of biaxial strain on interfacial intermixing and local structures in strain engineered GST-SL were studied. Highly (0 0 l ) textured GST-SL with thickness-varied Sb 2 Te 3 sublayers were fabricated by magnetron sputtering and investigated with multiple analyses on surfaces and interfaces. The appearance of Ge-Sb-Te alloys indicated the interfacial Ge/Sb intermixing in strain engineered GST-SL, which actually were composed of Sb 2 Te 3 quintuple layers, Ge-Sb-Te vdW layers and isolated GeTe bilayers. Grazing incidence x-ray diffraction (GID) and x-ray photoelectron spectroscopy (XPS) results revealed that biaxial strain not only facilitated the interfacial intermixing, but also caused the reconfiguration of Ge-Sb-Te vdW layers. Raman spectra indicated that vertical and in-plane vibrations of GeTe layers were not affected by the interfacial intermixing and the newly-formed Ge-Sb-Te layers had similar vibration characteristics as that of GeTe layers. A modified switching mechanism of GST-SL, relating to both the amorphous-crystalline phase transition of GeTe and Ge-Sb-Te layers incorporated into the Sb 2 Te 3 matrix, was then presented. The present studies shed new light on strain engineering for GST-SL and indicate their potential optoelectronic applications.

A major obstacle during the design of brain–computer interfaces is the unavailability of a neural implantable device that is µ-scale in size and is wireless, self-powered, and long-lasting. The current state-of-the-art implantable devices suffer from various limitations. Electromagnetic-based wireless devices are big in size because of their large antenna, which must be larger than one-tenth of the wavelength of the operational frequency. Ultrasound-based wireless devices, in addition to their low data rate, have massive loss in the skull and need an intermediate electromagnetic transceiver under the skull. Furthermore, almost all state-of-the-art wireless devices use micro-electrodes for neuronal recording, which are not reliable in long-term monitoring applications because of the direct contact between the tissue and metal electrodes. In this paper, we propose a novel, wireless, and ultra-compact implantable device termed NanoNeuroRFID. At the core of this device, there is a magnetoelectric (ME) antenna array. ME antennas are smart and ultra-miniaturized (

A state-of-the-art gas sensor is developed to measure extremely small concentrations of a chemical vapor in the air in a range lower than 0.1 parts per billion. The sensor enables simultaneous measurement of a chemical (methyl salicylate) with a resonant electromagnetic structure and radiating the information back to a base station. The chemical sensor is composed of a layer of graphene (transduction layer) with a molecular imprinting polymer (MIP) layer (sensor) on top. This leads to a combination of the ultra high sensitivity of graphene with the exquisite selectivity of the molecular imprinting technique (MIT). The sensor is electrically embedded within a patch antenna. The simulation results using Ansoft high-frequency structure simulator (HFSS) are presented along with test data that show parts per trillion (ppt) detection levels.

Spin-orbit coupling (SOC), the interaction between the electron spin and the orbital angular momentum, can unlock rich phenomena at interfaces, in particular interconverting spin and charge currents. Conventional heavy metals have been extensively explored due to their strong SOC of conduction electrons. However, spin-orbit effects in classes of materials such as epitaxial 5d-electron transition metal complex oxides, which also host strong SOC, remain largely unreported. In addition to strong SOC, these complex oxides can also provide the additional tuning knob of epitaxy to control the electronic structure and the engineering of spin-to-charge conversion by crystalline symmetry. Here, we demonstrate room-temperature generation of spin-orbit torque on a ferromagnet with extremely high efficiency via the spin-Hall effect in epitaxial metastable perovskite SrIrO3. We first predict a large intrinsic spin-Hall conductivity in orthorhombic bulk SrIrO3 arising from the Berry curvature in the electronic band structure. By manipulating the intricate interplay between SOC and crystalline symmetry, we control the spin-Hall torque ratio by engineering the tilt of the corner-sharing oxygen octahedra in perovskite SrIrO3 through epitaxial strain. This allows the presence of an anisotropic spin-Hall effect due to a characteristic structural anisotropy in SrIrO3 with orthorhombic symmetry. Our experimental findings demonstrate the heteroepitaxial symmetry design approach to engineer spin-orbit effects. We therefore anticipate that these epitaxial 5d transition-metal oxide thin films can be an ideal building block for low-power spintronics.

Phase change materials (PCMs) are highly promising for the digital-storage technology based on the fast phase transition between the crystal and amorphous states. In order to optimize the properties of PCMs, the doping of PCMs has become research hot points nowadays. In this paper, effects of Sn doping (0%, 10%, 30%) on the crystallization behavior of Ge2Sb2Te5 (GST) films induced by a picosecond pulsed laser with Gaussian energy profile were investigated experimentally. As compared to the previous study irradiated by a nanosecond pulsed laser, such factors as melting, ablation and crystallization thresholds dropped remarkably by a picosecond laser irradiation, and with the increase of Sn content those factors were further decreased. Due to the replacement of Ge atoms by Sn atoms, the Sn incorporation expanded the lattice constant so as to introduce the mechanical stress which, together with the thermal stress generated after laser irradiation, significantly affected the atomic movement during the crystallization process. High-resolution transmission electron microscopy (HRTEM) observations showed that GST with a lower Sn content of 10% tended to form sub-grain boundaries by local atomic shear to ensure long-range ordering of crystals, but with the increase of the Sn doping to 30%, the long-range ordering structure was broken, instead of some atoms arranged randomly, which were mainly Ge atoms, separating out from the lattice because of the replacement by Sn atoms. These extra Ge atoms were not involved in the crystallization process, proved by the Raman spectroscopy. The present study is fundamental for the design of advanced storage device based on PCMs.

In this paper, crystallization characteristics of amorphous Ge2Sb2Te5 (a-GST) films induced by a Gaussian picosecond laser with different laser fluence were carried out using transmission electron microscopy (TEM), Raman spectra and ab initio molecular dynamics (AIMD) simulations. TEM observations presented a solid-state phase transition with nanocrystalline microstructure at lower fluence, while a liquid-solid phase transition accompanied by an ingot-like crystalline microstructure was found at higher fluence, including a central coarse and an outer fine equiaxed regions as well as a columnar crystal region between them. In spite of the remarkable difference in microstructure, the composition of different regions kept constant from the Energy Dispersive Spectrometer (EDS) measurements. Different phase change behavior and laser fluence affected the shift of Raman peaks due to the phase change stress and thermal stress. A laser irradiation coupled AIMD simulation was then developed to study the preferential nucleation possibility. AIMD simulation results indicated that a thermal process in the central coarse equiaxed regions, with a higher cooling rate (10 k/ps) generated by the Gaussian picosecond laser irradiation, reduced the nucleation rate remarkably, causing crystal nucleus have enough space to grow up even to the micrometer scale. This is different from the morphology induced by nano- or femtosecond pulsed laser.

Sol-gel method has been deployed for the synthesis of spherical shaped KFeO2 nanoparticles. Various characterizations such as structural, morphological and optical - Raman, UV–visible, Photoluminescence (PL) spectroscopy has been carried out. Transmission electron microscopy (TEM) revealed the spherical morphology of the KFeO2 nanoparticles. X-ray diffraction (XRD) study reveals that the synthesized nanoparticles possess orthorhombic phase with Pbca space group. The Raman study has been done to understand the possible active modes in KFeO2 nanoparticles. The Raman spectra discloses that there are three Raman active modes viz., A1g, Eg, T2g as well as eleven Raman absorption peaks corresponding to these modes in the KFeO2 nanoparticles. Photoluminescence spectrum of the synthesized nanoparticles has been done to understand the various electronic transitions happening in the material. Further, the CIE (International Commission on Illumination or Commission Internationale de l'eclairage) diagram have been plotted to check the presence of illuminating colors in KFeO2 nanoparticles.

A systematic investigation of the soft magnetism, the change of modulus of elasticity with magnetization ( $\Delta \sf{E}$ effect), magnetostriction, and microwave properties has been carried out on iron-gallium-carbon thin films over a wide carbon content range. The phase transformation of the Fe-Ga-C films from bcc polycrystalline to amorphous leads to excellent magnetic softness with a low coercivity of less than 1 Oe, high saturation magnetization, narrow ferromagnetic resonance linewidth at 10 GHz of 20 to 30 Oe, and an ultra-low Gilbert damping constant of 0.0027. A record high piezomagnetic coefficient of 9.71 ppm/Oe, high saturation magnetostriction constant of 81.2 ppm, and large $\Delta \sf{E}$ effect of −120 GPa at 500 nm were achieved.

Most of the next-generation implantable medical devices that are targeting sub-mm scale form factors are entirely powered wirelessly. The most commonly used form of wireless power transfer for ultra-small receivers is inductive coupling and has been so for many decades. This might change with the advent of novel microfabricated magnetoelectric (ME) antennas which are showing great potential as high-frequency wireless powered receivers. In this paper, we compare these two wireless power delivery methods using receivers that operate at 2.52 GHz with a surface area of 0.043 mm2. Measurement results show that the maximum achievable power transfer of a ME antenna outperforms that of an on-silicon coil by approximately 7 times for a Tx-Rx distance of 2.16 and 3.3 times for a Tx-Rx distance of 0.76 cm.

Nano- and micro-electromechanical systems (N/MEMSs) are traditionally based on electrostatic or piezoelectric coupling, which couples electrical and mechanical energy through acoustic resonator structures. Most recently, N/MEMS devices based on magnetoelectrics are gaining much attention. Unlike electrostatic or piezoelectric N/MEMS that rely on an AC electric field or voltage excitation, magnetoelecric N/MEMS rely on the electromechanical resonance of a magnetostrictive/piezoelectric bilayer heterostructure exhibiting a strong strain-mediated magnetoelectric coupling under the excitation of a magnetic field and/or electric field. As a consequence, magnetoelectric N/MEMS enable unprecedented new applications, ranging from magnetoelectric sensors, ultra-compact magnetoelectric antennas, etc. This Tutorial will first outline the fundamental principles of piezoelectric materials, resonator design, specifically different acoustic modes, and piezoelectric-based N/MEMS applications, i.e., radio frequency front end filters and infrared radiation sensors. We will then provide an overview of magnetoelectric materials and N/MEMS focusing on the governing physics of the magnetoelectric effect, magnetic material properties for achieving high magnetoelectric coupling, state-of-the-art magnetoelectric N/MEMS devices, and their respective applications.

This paper presents a miniaturized complementary-metal-oxide-semiconductor (CMOS) oscillator using microelectromechanical system (MEMS) resonating at 159 MHz frequency. The CMOS circuit is designed and simulated in 0.35,..,m XFAB technology. The fabricated magnetoelectric (ME) sensor offers quality factor of 653. The proposed oscillator provides a phase noise as low as -131.3 dBc/Hz at 10kHz and -137.9 dBc/Hz at 100 kHz offset frequencies while consuming 2.24 mW power.

Phase change materials help realize voltage tunable spin dynamics., Controlling magnetization dynamics is imperative for developing ultrafast spintronics and tunable microwave devices. However, the previous research has demonstrated limited electric-field modulation of the effective magnetic damping, a parameter that governs the magnetization dynamics. Here, we propose an approach to manipulate the damping by using the large damping enhancement induced by the two-magnon scattering and a nonlocal spin relaxation process in which spin currents are resonantly transported from antiferromagnetic domains to ferromagnetic matrix in a mixed-phased metallic alloy FeRh. This damping enhancement in FeRh is sensitive to its fraction of antiferromagnetic and ferromagnetic phases, which can be dynamically tuned by electric fields through a strain-mediated magnetoelectric coupling. In a heterostructure of FeRh and piezoelectric PMN-PT, we demonstrated a more than 120% modulation of the effective damping by electric fields during the antiferromagnetic-to-ferromagnetic phase transition. Our results demonstrate an efficient approach to controlling the magnetization dynamics, thus enabling low-power tunable electronics.

This paper introduces a behavioral circuit model for a magnetoelectric (ME) antenna, which is a novel miniaturized device with applications in low-power sensing. To facilitate the design of integrated circuits interfaced to the antenna, its model accounts for the amplitude modulation behavior observed during measurements of the nanoelectromechanical system (NEMS) device when subjected to an AC magnetic field and a DC biasing field. We propose a dynamic model for transient simulations, and show that the model characteristics match the experimentally obtained behavior of the ME antenna. As an example, the model is demonstrated through simulations of a sensor circuit for magnetic fields in the 282 microTesla to 28 milliTesla range.

Non-invasive deep brain stimulation has been a major challenge in the field of neuroscience and brain stimulation in the past three decades. Current brain stimulation technologies suffer from such hurdles as the inability to do deep brain stimulation, poor spatial resolution, and invasiveness. Transcranial magnetic stimulation (TMS) technique, for instance, cannot target brain regions deeper than ∼2cm and has a poor spatial resolution, impacting a large area of the peripheral region and leading to various side effects. Implantable electrodes, even though effective for deep brain stimulation, are invasive and carry various drawbacks related to the surgery and site infection. In this paper, we propose a new concept that relies on temporal interference of two high- frequency magnetic fields generated by two electromagnetic coils. The neural system does not respond to each of these high-frequency magnetic fields alone because of the intrinsic low-pass filtering properties of the neural membrane. The peripheral areas of the brain are impacted only by the high-frequency magnetic fields that cannot stimulate the nerves, while the deep brain area where the two fields interfere experiences a magnetic field that contains a low-frequency envelope and therefore the nerves can be stimulated. This technique can noninvasively focus a magnetic or electric beam at any depth inside the brain with a high resolution, without impacting the peripheral regions.

During different antenna miniaturization techniques, mechanically driven antennas have been demonstrated as the most effective method over state-of-the-art compact antennas. The magnetoelectric (ME) antennas based on a released magnetostrictive/piezoelectric heterostructure rely on electromechanical resonance instead of electromagnetic wave resonance, which results in a typical antenna size as small as one-thousandth of an electromagnetic wavelength. However, the microelectromechanical systems (MEMS) devices are very fragile and delicate due to their suspending structure. Here we show that solid mounted resonator (SMR)-based MEMS ME antennas can be realized with robust and high-gain performance. Although various packaging approaches are used to handle MEMS devices and protect them from environmental damage, these methods are complicated and high-cost. Compared to free-standing membrane ME antennas, SMR-based antennas are more structurally stable with no need for removing silicon substrate, but the design and fabrication of Bragg reflector layers must be carefully done to obtain the desired resonant frequency. In this work, 1D Mason model and 2D COMSOL finite element method (FEM) simulations were performed to design the SMR-based ME antennas. Then the in-plane radiation pattern of a fabricated antenna that operates at 1.75 GHz was characterized. Our results successfully demonstrate how to design, fabricate and test SMR-based ME antennas, which are provided with complementary metal-oxide-semiconductor (CMOS) process compatibility, size miniaturization, mechanical stability and high-gain performance. These miniaturized robust ME antennas are expected to have great influences on our future antennas for internet of things, wearable and bio-implantable applications, smart phones, wireless communication systems, etc.

In this work, a new ultra-compact antenna design based on magnetoelectric coupling effect for implantable wireless communication is introduced. This ME antenna is driven by acoustic wave and the resonance frequency is decided by the geometric size of resonator. An NPR antenna is fabricated by MEMS technology and tested. The size of one antenna resonator is 8×350µm2 and the whole antenna is designed to 730×940µm2 with 16 arrays in parallel. An antenna gain of −54.81dBi is achieved at the resonance frequency of 371.125MHz. The Q-factor of 123.1 is calculated by MBVD model. Because of the short wavelength of acoustic wave, the antenna size is effectively scaled down, which gives a new solution for the miniaturization of entire implantable device.

Since the revival of multiferroic laminates with giant magnetoelectric (ME) coefficients, a variety of multifunctional ME devices, such as sensor, inductor, filter, antenna etc. have been developed. Magnetoelastic materials, which couple the magnetization and strain together, have recently attracted ever-increasing attention due to their key roles in ME applications. This review starts with a brief introduction to the early research efforts in the field of multiferroic materials and moves to the recent work on magnetoelectric coupling and their applications based on both bulk and thin-film materials. This is followed by sections summarizing historical works and solving the challenges specific to the fabrication and characterization of magnetoelastic materials with large magnetostriction constants. After presenting the magnetostrictive thin films and their static and dynamic properties, we review micro-electromechanical systems (MEMS) and bulk devices utilizing ME effect. Finally, some open questions and future application directions where the community could head for magnetoelastic materials will be discussed.

Giant nonreciprocity in a SAW-based microwave isolator device is reported offering substantial size and performance advantages., Nonreciprocity, the defining characteristic of isolators, circulators, and a wealth of other applications in radio/microwave communications technologies, is generally difficult to achieve as most physical systems incorporate symmetries that prevent the effect. In particular, acoustic waves are an important medium for information transport, but they are inherently symmetric in time. In this work, we report giant nonreciprocity in the transmission of surface acoustic waves (SAWs) on lithium niobate substrate coated with ferromagnet/insulator/ferromagnet (FeGaB/Al2O3/FeGaB) multilayer structure. We exploit this structure with a unique asymmetric band diagram and expand on magnetoelastic coupling theory to show how the magnetic bands couple with acoustic waves only in a single direction. We measure 48.4-dB (power ratio of 1:69,200) isolation that outperforms current state-of-the-art microwave isolator devices in a previously unidentified acoustic wave system that facilitates unprecedented size, weight, and power reduction. In addition, these results offer a promising platform to study nonreciprocal SAW devices.

There is currently a need for an efficient approach to control magnetism at small scales (

Magnetic materials are the necessary components of the modern rf components. The demand for higher communication speed such as the upcoming 5G network requires higher operation frequency of rf components. For example, the future spectrum band of mobile network will be extended above 24 GHz [1]. Permeability measurements provide a basis for the design and characterization of magnetic materials and the development of RF devices. However, permeability measurement results and commercially available permeameters have been limited to 9GHz or below [2]–[7]. Conventional broadband permeameters use a vector network analyzer (VNA), and a pick-up coil or an electric short [2], [3], or a broadband transmission line [4], [6] for magnetically exciting the materials under test. Inductance changes are measured at zero magnetic field and at saturation magnetic field through a vector network analyzer for extracting the permeability spectrum. The bandwidth of Pick-up coil is limited to several hundred MHz. Transmission-lines [4]–[6] are widely used for broadband permeameters. However, the transmission-line type permeameters are noisy in the frequency range below 100MHz due to the low inductance. In addition, all these broadband permeameters based on vector network analyzers are expensive, and not reliable in measuring thin films or materials with low permeability because of the low signal to noise ratio (SNR). In this article, we demonstrate a new type of permemeter for ultra-wide band permeability measurements with significantly enhanced signal to noise ratio (SNR), and demonstrate the measurements on a 50nm FeGaB film up to 22GHz and an ultra-thin 2nm NiFe film. This permeameter enables the characterization of the complex permeability between 10MHz-26GHz, as well as many other typical magnetic parameters including linewidth, saturation magnetization, effective anisotropy field, Gilbert damping, and inhomogeneous linewidth broadening. In addition, the new permeability measurement system shows $40 \sim 50$ dB higher SNR over the conventional permeameters.

Strong strain-mediated magnetoelectric (ME) coupling in magnetic/ferroelectric heterostructures has great potential for different high-frequency multiferroic devices. In this article, we present the most recent progress in integrated multiferroic devices. Integrated magnetic tunable inductors with a wide operation frequency range, integrated nonreciprocal bandpass filters with dual magnetic and electric-field tunability based on magnetostatics surface waves, and novel radio-frequency nanomechanical ME resonators with pico-Tesla sensitivity for direct current magnetic fields are presented. Finally, a new antenna miniaturization mechanism, acoustically actuated nanomechanical ME antennas, which can successfully miniaturize the size by 1–2 orders, is introduced. With the advantages of high magnetic field sensitivity, highest antenna gain among all nanoscale antennas at similar frequency, integrated capability with complementary metal oxide semiconductor technology, and ground-plane immunity from metallic surfaces and the human body, ME antennas have a bright future for biomedical applications, wearable antennas, and the Internet of Things due to their unique and particular properties.

Strong magnetoelectric (ME) coupling realized in magnetic/ferroelectric multiferroic heterostructures provides great potential for different integrated multiferroic devices for sensing, power, RF, and µ-wave electronics. Here, we present the most recent progress on new integrated multiferroic devices including novel integrated magnetic tunable inductors with a wide operation frequency range; integrated nonreciprocal bandpass filter with dual H- and E-field tunability based on magnetostatics surface waves; dual H- and E-field tunable RF bandpass filters with nanomechanical ME resonators; RF nanomechanical ME resonators with pico-Tesla DC magnetic fields sensitivity; a new antenna miniaturization mechanism, acoustically actuated nanomechanical ME antennas, which successfully miniaturize the magnitude in 1–2 orders with the advantages of the high magnetic field sensitivity, highest antenna gain within all nanoscale antennas at the similar frequency, and ground plane immunity on the metallic surface and the human body.