Magnetoelectric Heterostructures Research Articles

Giant low-frequency multipeak self-biased magnetoelectric properties in four-phase structure with stepped ultrasonic horn

This paper develops a self-biased magnetoelectric (ME) heterostructure FeCuNbSiB/terfenol-d/ultrasonic-horn/PZT by sandwiching a piezoelectric Pb(Zr,Ti)O3 (PZT) plate and a magnetization-graded FeCuNbSiB/terfenol-d layer on a rectangular-stepped ultrasonic horn substrate. The rectangular-stepped ultrasonic horn substrate severs as the resonance frequency determining element of the ME heterostructure, converges and amplifies the vibration excited by the magnetization-graded FeCuNbSiB/terfenol-d layer. The experiments show that fifteen large peaks of ME response with magnitudes of 0.2–7.5 V/(cm·Oe) in 0.5–50 kHz range are observed at zero-biased magnetic field. This demonstrates that the proposed multi-peak self-biased heterostructure may be useful for multifunctional devices for multi-frequency operation.

Temperature dependence of magnetoelectric coupling in La0.7Sr0.3MnO3/BaTiO3 layered heterostructure with various volume fraction

The epitaxial La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) layered heterostructures were grown onto (001) oriented LaAlO3 single-crystal substrate by pulsed laser deposition. Temperature dependence of the magnetoelectric (ME) voltage coefficient (αE) was studied for the heterostructures over temperature range of −20–85°C (253.15–358.15K). The values of αE for all of the samples exhibit a monotonous decreasing tendency with increasing temperature. Moreover, the variation in ME voltage coefficient as a function of temperature was found to be significantly dependent on the volume fraction of BTO layer. Our results showed that maximum number of the volume fraction of BTO layer can provide more stable ME voltage coefficient in wide temperature range, due to the competition of the effects of temperature influenced piezoelectricity, magnetostriction, and electrical transport property of the constituents. This finding could provide an available method for promote miniaturization of the ME heterostructure devices in view of temperature stability.

Tamm states in graphene-based different combined magneto-electric superlattice heterostructures

Tamm states localized at the interface between a homogeneous potential barrier and a combined magneto-electric potential barriers superlattice in monolayer graphene have been theoretically investigated. The results show that the symmetries of Tamm states are different when the components of the superlattice are different. When the single unit of the superlattice consists of double anti-parallel potential barriers and two gaps, Tamm states present symmetry about momentum wave vector ky′=0 at the same intensity of the homogeneous potential barrier (Vs). When the single unit of the superlattice consists of double anti-parallel magnetic potential barriers and two gaps, it demonstrates that Tamm states at positive Vs are symmetric to that at negative Vs about the electron incident energy E0=0. When the single unit of the superlattice consists of double anti-parallel combined magneto-electric potential barriers, the band gap at Dirac point is opened, Tamm states exhibit no symmetry about ky′ or the electron incident energy whether at the same Vs or at positive and negative Vs.

Investigation of the influence of various factors on the dielectric, piezoelectric, and magnetoelectric properties of 1-3, 3-1, and 1-1 multiferroic composites

Technique to fabricate magnetoelectric piezoelectric/magnetostrictive ferrite composites with 1-3, 3-1, 1-1 connectivities through binding uniformed by size and package ceramic elements was developed. Advantage of this technique is the use of piezoceramic which was previously poled under optimal conditions; this is important, because piezoelectric phase embedded in magnetoelectric composite is difficult to pole due to the high electrical conductivity of adjacent ferrite phase. The effect of piezoelectric material type, volume ratio of phases, and linear size of repeating fragment on the dielectric, piezoelectric, and magnetoelectric properties of ν PZT + (1−ν) NiCo0.02Cu0.02Mn0.1Fe1.8O4−δ ( v – volume fraction of piezoelectric, PZT – commercial grades of lead–zirconate–titanate such as PZT-36, PZTNB-1, PZTST-2, PZTTBS-2, PZT-19) composites is studied. It is shown that, with an equal volume ratio of phases, composites based on piezoceramics with high piezoelectric voltage coefficient gij (PZT-36, PZTNB-1) exhibit the most prominent magnetoelectric coupling efficiency. Decrease in the linear size of repeating fragment lΣ also contributes to an increase in Δ E/Δ H coefficient. Given other conditions being equal, 1-1 type composites commonly exhibit the highest values of magnetoelectric coefficient. Maximal values of magnetoelectric coefficient Δ E/Δ H for 0.5 PZT-36 + 0.5 NiCo0.02Cu0.02Mn0.1Fe1.8O4−δ magnetoelectric heterostructures reach ∼500 mV/(cm·Oe) at a frequency of 1 kHz.

Magnetoelectric control of spin currents

The ability to control the spin current injection has been explored on a hybrid magnetoelectric system consisting of a (011)-cut ferroelectric lead magnesium niobate-lead titanate (PMNT) single crystal, a ferromagnetic FePt alloy, and a metallic Pt. With this PMNT/FePt/Pt structure we have been able to control the magnetic field position or the microwave excitation frequency at which the spin pumping phenomenon between FePt and Pt occurs. We demonstrate that the magnetoelectric heterostructure operating in the L-T (longitudinal magnetized-transverse polarized) mode couples the PMNT crystal to the magnetostrictive FePt/Pt bilayer, displaying a strong magnetoelectric coefficient of ∼140 Oe cm kV−1. Our results show that this mechanism can be effectively exploited as a tunable spin current intensity emitter and open the possibility to create an oscillating or a bistable switch to effectively manipulate spin currents.

ChemInform Abstract: Low Energy Consumption Spintronics Using Multiferroic Heterostructures

We review the recent progress in the field of multiferroic magnetoelectric heterostructures. The lack of single phase multiferroic candidates exhibiting simultaneously strong and coupled magnetic and ferroelectric orders led to an increased effort into the development of artificial multiferroic heterostructures in which these orders are combined by assembling different materials. The magnetoelectric coupling emerging from the created interface between the ferroelectric and ferromagnetic layers can result in electrically tunable magnetic transition temperature, magnetic anisotropy or magnetization reversal. The full potential of low energy consumption magnetic based devices for spintronics lies in our understanding of the magnetoelectric coupling at the scale of the ferroic domains. Although the thin film synthesis progresses resulted into the complete control of ferroic domain ordering using epitaxial strain, the local observation of magnetoelectric coupling remains challenging. The ability to imprint ferroelectric domains into ferromagnets and to manipulate those solely using electric fields suggests new technological advances for spintronics such as magnetoelectric memories or memristors.

A differential magnetoelectric heterostructure: Internal noise reduction and external noise cancellation

A differential heterostructure design which has a capability to reduce the internal noise and reject the external vibration noise for Metglas magnetostrictive foils/Pb(Zr, Ti)O3 piezofiber based-magnetoelectric (ME) laminated composite has been studied. The internal noise reduction is equivalent to that offered by sensor array stacks, and the external noise cancellation is based on a differential method (i.e., ME signal is in-phase but vibration noise is anti-phase). The ability of the structure to reduce the internal noise, and cancel the external vibration noise by a 10-fold attenuation factor, allows for practical applications of these sensors in real-world environments where contamination of magnetic signals by external vibrational noise increases the equivalent magnetic noise.

The E-Field-Induced Volatile and Nonvolatile Magnetization Switching of CoNi Thin Films in CoNi/PMN-PT Heterostructures

In this paper, we report the giant electric-field (E-field)-induced magnetic anisotropy and magnetization switching in CoNi/Pb(Mg1/3Nb2/3)O3– x PbTiO3(PMN-PT) magnetoelectric heterostructures. For CoNi/PMN-30%PT, the E-field-induced anisotropy shows a volatile behavior; whereas for CoNi/PMN-32%PT, a large and nonvolatile E-field-induced anisotropy field up to 54 kA/m is observed. These behaviors can be understood by measuring the strain versus the E-field curves of two kinds of substrates. On the basis of the E-field-induced nonvolatile magnetic switching, two stable magnetization states defined by applying E-field pulses were demonstrated in CoNi/PMN-32%PT heterostructure, which paves a new way for voltage-write magnetic random memory devices.

Resonant Magnetoelectric Effect in Winglike Magnetoelectric Composites of Fe-Based Nanocrystalline FeCuNbSiB Alloy and Piezoelectric Ceramic Pb(Zr,Ti)O<sub>3</sub> With Middle Bonding

Magnetoelectric (ME) composites consisting of piezoelectric materials and magnetostrictive materials have been studied extensively due to their large ME effects than those in single phases [1-2], offering promise for magnetic moment sensing and other applications. In these composites, the ME coefcient is dependent upon the elastic coupling that occurs at the interface between piezoelectric and magnetostrictive phases. Therefore, the interfacial coupling is a key factor that determines the ME response of layered composites. In fact, there is no ideal interfacial coupling for the classical strain mediated ME laminated composites, because they are usually constructed layer by layer through interface bonding with epoxy adhesive. This kind of non-ideal interface bonding can dampen the generated strain and mechanical quality factor, cause frequency shift, and also contribute to the noise oor and aging [3]. Recently, some studies have attempted to achieve ME responses, which are not inuenced by interfacial conditions. A stretching mechanically mediated structure of TbFe 2 / PZT/TbFe 2 with two nonmagnetic akes is designed to achieve the ME coupling by end bonding instead of interface bonding [4]. A ME heterostructure made by attaching magnetostrictive Metglas at the free ends of a PZT plate exhibits large ME response [5]. However, there are still too much interfacial contact exist, at least two end contacts. The influence of interfacial contact can be further decreased by new structure.

Generation of localized strain in a thin film piezoelectric to control individual magnetoelectric heterostructures

Experimental results demonstrate the ability of a surface electrode pattern to produce sufficient in-plane strain in a PbZr0.52Ti0.48O3 (PZT) thin film clamped by a Si substrate to control magnetism in a 1000 nm diameter Ni ring. The electrode pattern and the Ni ring/PZT thin film heterostructure were designed using a finite element based micromagnetics code. The magnetoelectric heterostructures were fabricated on the PZT film using e-beam lithography and characterized using magnetic force microscopy. Application of voltage to the electrodes moved one of the “onion” state domain walls. This method enables the development of complex architectures incorporating strain-mediated multiferroic devices.

Effective 90-degree magnetization rotation in Co2FeAl thin film/piezoelectric system probed by microstripline ferromagnetic resonance

Microstripline ferromagnetic resonance technique has been used to study the indirect magnetoelectric coupling occurring in an artificial magnetoelectric heterostructure consisting of a magnetostrictive thin film cemented onto a piezoelectric actuator. Two different modes (sweep-field and sweep-frequency modes) of this technique have been employed to quantitatively probe the indirect magnetoelectric coupling and to observe a voltage induced magnetization rotation (of 90°). This latter has been validated by the experimental frequency variation of the uniform mode and by the amplitude of the sweep-frequency spectra.

Enhanced bending-resonance magnetoelectric response in end-bonding magnetostrictive/piezoelectric heterostructure

In this paper, we present a magnetoelectric (ME) heterostructure made by attaching two magnetostrictive Nickel (Ni) plates at the two free ends of a piezoelectric Pb(Zr1-xTix)O3 (PZT) plate. With this configuration, the Ni and the PZT plates vibrate more freely due to the absence of an interfacial epoxy layer, which results in a larger bending deformation of the PZT plate. The Ni and the PZT plates couple to each other by mechanical magnetic forces, instead of shear forces. In addition, the two Ni plates act as proof masses for the PZT plate, which can reduce the bending resonant frequency (f r) the of PZT plate. The experimental results demonstrate that the bendingresonance ME voltage coefficient (aME,r) is 2.82 times larger than that of the traditional bilayer laminate Ni/PZT. As the length of the Ni plates (L) increases, the fr decreases and can be shifted in a range of 34.6 kHz ≤ fr ≤ 61.02 kHz. The maximum aME,r of 49.84 V/cm Oe is observed at dc bias magnetic field H dc = 158 Oe when L = 18 mm. This heterostructure is of interest for high-sensitive dc magnetic-field sensors, ME transducers.

Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure.

Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.

Magnetoelectric quasi-(0-3) nanocomposite heterostructures.

Magnetoelectric composite thin films hold substantial promise for applications in novel multifunctional devices. However, there are presently shortcomings for both the extensively studied bilayer epitaxial (2-2) and vertically architectured nanocomposite (1-3) film systems, restricting their applications. Here we design a novel growth strategy to fabricate an architectured nanocomposite heterostructure with magnetic quasiparticles (0) embedded in a ferroelectric film matrix (3) by alternately growing (2-2) and (1-3) layers within the film. The new heteroepitaxial films not only overcome the clamping effect from substrate, but also significantly suppress the leakage current paths through the ferromagnetic phase. We demonstrate, by focusing on switching characteristics of the piezoresponse, that the heterostructure shows magnetic field dependence of piezoelectricity due to the improved coupling enabled by good connectivity amongst the piezoelectric and magnetostrictive phases. This new architectured magnetoelectric heterostructures may open a new avenue for applications of magnetoelectric films in micro-devices.

Artificial multiferroic heterostructures for an electric control of magnetic properties

The control of magnetism by electric fields is an important goal for future low-power spintronics devices. This partly explains the intensified recent interest for magnetoelectric multiferroic materials and heterostructures. The lack of ferro- or ferrimagnetic–ferroelectric materials with large magnetoelectric coupling between the two orders has spurred intensive research on artificial multiferroics combining ferroelectric or piezoelectric materials and ferromagnets. In this paper we review synthetically the potential of thin-film-based heterostructures in which a magnetic film is in contact with a ferroelectric or piezoelectric one to obtain an electric control of magnetic properties. This electric control either results from a strain-induced magnetoelectric coupling, a charge-driven one, or from the modulation of an interfacial exchange-bias interaction. Contrôler électriquement les propriétés magnétiques des matériaux et réaliser ainsi de nouveaux composants faiblement consommateurs en énergie est un des enjeux de la future électronique de spin. Ceci explique l'intérêt considérable porté aux matériaux et architectures multiferroïques. Malgré des recherches intenses, le graal d'un composé à la fois ferroélectrique et ferro- ou ferrimagnétique à température ambiante avec un fort couplage magnétoélectrique entre ces deux propriétés n'a pas encore été trouvé. Pour pallier ce manque, de nombreux travaux ont porté sur les multiferroïques artificiels, hétérostructures combinant un matériau ferroélectrique ou piézoélectrique et un composé ferromagnétique. Cet article constitue une revue succincte du potentiel de ces hétérostructures en géométrie planaire pour obtenir un contrôle électrique des propriétés magnétiques. Un tel contrôle peut être obtenu par un effet magnétoélectrique indirect basé sur un couplage d'origine élastique, de façon directe par une modulation des charges dans le ferromagnétique induite par la ferroélectricité ou encore en exploitant le couplage d'échange à l'interface entre un multiferroïque et un matériau magnétique.

Electrically tunable microwave properties in NiFeTa/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) magnetoelectric heterostructures

The studied magnetoelectric heterostructure consisting of a NiFeTa thin film grown onto a [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) (PMN-PT) substrate was prepared by using gradient-composition sputtering technique. A shorted micro-strip transmission-line perturbation method using a vector network analyzer was employed to study the electrical field modulation of microwave properties of the NiFeTa/PMN-PT heterostructure. It was found that the resonance frequency of the sample can be tuned from 1.72 GHz to 2.05 GHz when the applied electrical field is varied from −6 kV/cm to 6 kV/cm. Moreover, we experimentally observed a quasi-linear relationship between the resonance frequency and the electrical field in a wide range of electrical field from 0 kV/cm to 6 kV/cm in the heterostructure, which is suggested to be useful for applications. All the results are discussed taking into account the reverse magnetostrictive effect and the reverse piezoelectric effect.

Large self-biased magnetoelectric response in four-phase heterostructure with multiple low-frequency peaks

This paper develops a self-biased magnetoelectric (ME) heterostructure FeCuNbSiB/Terfenol-D/Be-bronze/Pb(Zr,Ti)O3 (PZT) by sandwiching a nonmagnetic elastic Be-bronze plate between an piezoelectric PZT plate and a magnetization-graded FeCuNbSiB/Terfenol-D layer. The Be-bronze plate severs as the resonance frequency determining element of the ME heterostructure. By using the magnetization-graded magnetostrictive layer and the elastic Be-bronze plate, seven large peaks of ME response with magnitudes of 0.3–10 (V/cm Oe) in 1–70 kHz range are observed at zero-biased magnetic field. This demonstrates that the proposed multi-peak self-biased heterostructure may be useful for multifunctional devices such as multi-frequency energy harvesters or low-frequency ac magnetic field sensors.

Giant 2-D Magnetoelectric Effects in a Unique Magnetostrictive/Piezoelectric Heterostructure Without Interface Bonding

We develop a unique magnetoelectric (ME) heterostructure with giant 2-D ME effects by attaching magnetostrictive Metglas at the free end of a piezoelectric Pb(Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PZT) cantilever, instead of interface bonding. The ME effects originate from flexural deformation of PZT plate driven by a mechanical force from Metglas. In experiments, the 1-D ME heterostructures induced different directional magnetic fields have been designed optimally. When the length of Metglas ribbon is 12 mm, the 1-D ME heterostructures have the maximum ME effects. After assembling the different optimal designed 1-D ME heterostructures, an ME heterostructure with 2-D ME characteristics is obtained. The 2-D heterostructure has two resonant frequencies, at about 88 and 115 kHz. The maximum resonant voltage coefficient (α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ME,r</sub> ) is 79 (V/cm Oe) when the heterostructure is in one direction of the magnetic field, and 45 (V/cm Oe) when the heterostructure is in the other direction of the magnetic field. The results demonstrate that this ME structure can be used as a multidimensional ME transducer.

Combining ferromagnetic resonator and digital image correlation to study the strain induced resonance tunability in magnetoelectric heterostructures.

This paper reports the development of a methodology combining microstrip ferromagnetic resonance and digital image correlation in order to simultaneously measure the voltage-induced strains and the magnetic resonance in artificial magnetoelectric heterostructures ("magnetic films/piezoelectric substrate" or "magnetic films/flexible substrate/piezoelectric actuator"). The overall principle of the technique and the related analytical modelling are described. It is powerful to estimate the magnetostriction coefficient of ferromagnetic thin films and can be used to determine the effective magnetoelectric coefficient of the whole heterostructures in addition to the piezoelectric coefficient related to the in-plane voltage-induced strains. This methodology can be applied to system for which the strains are well transmitted at the different interfaces.

Electric-field-controlled interface strain coupling and non-volatile resistance switching of La1-xBaxMnO3 thin films epitaxially grown on relaxor-based ferroelectric single crystals

We have fabricated magnetoelectric heterostructures by growing ferromagnetic La1-xBaxMnO3 (x = 0.2, 0.4) thin films on (001)-, (110)-, and (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb1/2)O3-0.34PbTiO3 (PINT) ferroelectric single-crystal substrates. Upon poling along the [001], [110], or [111] crystal direction, the electric-field-induced non-180° domain switching gives rise to a decrease in the resistance and an enhancement of the metal-to-insulator transition temperature TC of the films. By taking advantage of the 180° ferroelectric domain switching, we identify that such changes in the resistance and TC are caused by domain switching-induced strain but not domain switching-induced accumulation or depletion of charge carriers at the interface. Further, we found that the domain switching-induced strain effects can be efficiently controlled by a magnetic field, mediated by the electronic phase separation. Moreover, we determined the evolution of the strength of the electronic phase separation against temperature and magnetic field by recording the strain-tunability of the resistance [(ΔR/R)strain] under magnetic fields. Additionally, opposing effects of domain switching-induced strain on ferromagnetism above and below 197 K for the La0.8Ba0.2MnO3 film and 150 K for the La0.6Ba0.4MnO3 film, respectively, were observed and explained by the magnetoelastic effect through adjusting the magnetic anisotropy. Finally, using the reversible ferroelastic domain switching of the PINT, we realized non-volatile resistance switching of the films at room temperature, implying potential applications of the magnetoelectric heterostructure in non-volatile memory devices.