Magnetoelectric Heterostructures Research Articles

Electric Control of the Magnetic Domains in Artificial Magnetoelectric Composite Heterostructure

Magnetic force microscopy (MFM) has been used to probe the influence of an in situ applied in-plane elastic strains and/or magnetic field on the static magnetic configuration of a 530 nm magnetostrictive FeCuNbSiB thin film. The film shows a typical magnetic stripe domain configuration with 180 nm magnetic domain width presenting its magnetic moments oriented perpendicularly to the film plane. The in-plane strain was induced via the application of a voltage in a piezoelectric (PE) actuator on which the film/substrate system was glued. The FeCuNbSiB film was deposited onto a compliant polyimide substrate (Kapton) in order to avoid clamping effects that can lead to low transmission of strains from the actuator to the film/substrate system. The instrumental setup was modified with a custom-built electromagnet for performing in situ MFM experiments under the application of an in-plane magnetic field. We could compare the strain-mediated effect upon the magnetic domain configuration with the effect of an applied magnetic field. This paper clearly shows a better-defined electric field/strain control of the local domain magnetization (size and orientation). The efficient coupling between the magnetostrictive properties of the FeCuNbSiB film and the PE ones of the actuators allows a complete switching of the out-of-plane domain magnetization toward an in-plane homogeneous magnetic one. This magnetoelectric heterostructure can thus open the way for new devices allowing the electric control of the magnetic information at the nanoscale level.

Thickness dependence of magnetoelectric properties for Pb(Zr0.52Ti0.48)O3/La0.67Sr0.33MnO3 heterostructures

In this work, magnetoelectric thin film heterostructures of Pb(Zr0.52Ti0.48)O3/La0.67Sr0.33MnO3(PZT/LSMO) were epitaxially grown on SrTiO3(STO) substrates. aa-phase and r-phase in PZT layer could be observed simultaneously. Thickness dependent magnetoelectric effect of these heterostructures is investigated in detail. The results show that the r-phase in PZT layer will significantly improve the magnetoelectric voltage coefficient (αE31), and the amount of r-phase will decrease with increasing thickness of PZT layer. The maximum αE31 can reach 1153 mV/cm Oe for the sample with PZT thickness of 32 nm. This work will be of significance for tuning magnetoelectric effect via thickness ratio between ferroelectric and ferromagnetic layers.

Resonance of magnetization excited by voltage in magnetoelectric heterostructures

Manipulation of magnetization dynamics is critical for spin-based devices. Voltage driven magnetization resonance is promising for realizing low-power information processing systems. Here, we show through Finite Element Method (FEM) simulations that magnetization resonance in nanoscale magnetic elements can be generated by a radio frequency (rf) voltage via the converse magnetoelectric (ME) effect. The magnetization dynamics induced by voltage in a ME heterostructures is simulated by taking into account the magnetoelastic and piezoelectric coupling mechanisms among magnetization, strain and voltage. The frequency of the excited magnetization resonance is equal to the driving rf voltage frequency. The proposed voltage driven magnetization resonance excitation mechanism opens a way toward energy-efficient spin based device applications.

360° deterministic magnetization rotation in a three-ellipse magnetoelectric heterostructure

A magnetic dipole-coupled magnetoelectric heterostructure comprised of three closely spaced ellipse shapes was designed and shown to be capable of achieving deterministic in-plane magnetization rotation. The design approach used a combination of conventional micromagnetic simulations to obtain preliminary configurations followed by simulations using a fully strain-coupled, time domain micromagnetic code for a detailed assessment of performance. The conventional micromagnetic code has short run times and was used to refine the ellipse shape and orientation, but it does not accurately capture the effects of the strain gradients present in the piezoelectric and magnetostrictive layers that contribute to magnetization reorientation. The fully coupled code was used to assess the effects of strain and magnetic field gradients on precessional switching in the side ellipses and on the resulting dipole-field driven magnetization reorientation in the center ellipse. The work led to a geometry with a CoFeB ellipse (125 nm × 95 nm × 4 nm) positioned between two smaller CoFeB ellipses (75 nm × 50 nm × 4 nm) on a 500 nm PZT-5H film substrate clamped at its bottom surface. The smaller ellipses were oriented at 45° and positioned at 70° and 250° about the central ellipse due to the film deposition on a thick substrate. A 7.3 V pulse applied to the PZT for 0.22 ns produced 180° switching of the magnetization in the outer ellipses that then drove switching in the center ellipse through dipole-dipole coupling. Full 360° deterministic rotation was achieved with a second pulse. The temporal response of the resulting design is discussed.

Cyclable and non-volatile electric field control of magnetism in BiFeO3 based magnetoelectric heterostructures

Room temperature manipulation of the ferromagnetic state via an electric field is investigated in Ni/BiFe0.95Mn0.05O3 thin film heterostructures. A 600% increase in the magnetic coercive field of the Ni layer is observed at the initial DC electrical poling of the ferroelectric BiFe0.95Mn0.05O3 layer. The magnetoelectric effect is remanent, and the magnetic coercive field can be modulated between a low value and a high value by successively switching the ferroelectric polarization. After the initial poling, the coercive field difference is decreased by subsequent back and forth switching. However, the magnetic bi-stability is preserved at least up to 250 cycles, which is promising for spintronic applications.

Magnetoelectricity of CoFe2O4 and tetragonal phase BiFeO3 nanocomposites prepared by pulsed laser deposition

The coupling between the tetragonal phase (T-phase) of BiFeO3 (BFO) and CoFe2O4 (CFO) in magnetoelectric heterostructures has been studied. Bilayers of CFO and BFO were deposited on (001) LaAlO3 single crystal substrates by pulsed laser deposition. After 30 min of annealing, the CFO top layer exhibited a T-phase-like structure, developing a platform-like morphology with BFO. Magnetic hysteresis loops exhibited a strong thickness effect of the CFO layer on the coercive field, in particular along the out-of-plane direction. Magnetic force microscopy images revealed that the T-phase CFO platform contained multiple magnetic domains, which could be tuned by applying a tip bias. A combination of shape, strain, and exchange coupling effects are used to explain the observations.

Magnetoelectric heterostructure and device application

The magnetoelectric (ME) heterostructure is composed of ferromagnetic and ferroelectric materials. The heterostructural ME effect originates from piezoelectric effect in the ferroelectric component and magnetostrictive effect in the ferromagnetic component. The magnetoelectric heterostructure has higher magnetoelectric coupling coefficient and lower dielectric loss than the particulate composites, and thus leading to several promising applications such as in the magnetic field sensors, the energy harvesters, antenna and memory devices. In this paper, we review the recent research progress in ME heterostructure for device applications, and present a development course of ME heterostructure. Finally, we also summarize the challenges of developing the ME heterostructure and point out its perspectives.

Magnetic field response of doubly clamped magnetoelectric microelectromechanical AlN-FeCo resonators

Magnetoelectric (ME) cantilever resonators have been successfully employed as magnetic sensors to measure low magnetic fields; however, high relative resolution enabling magnetometry in high magnetic fields is lacking. Here, we present on-chip silicon based ME microelectromechanical (MEMS) doubly clamped resonators which can be utilized as high sensitivity, low power magnetic sensors. The resonator is a fully suspended thin film ME heterostructure composed of an active magnetoelastic layer (Fe0.3Co0.7), which is strain coupled to a piezoelectric signal/excitation layer (AlN). By controlling uniaxial stress arising from the large magnetoelastic properties of magnetostrictive FeCo, a magnetically driven shift of the resonance frequency of the first fundamental flexural mode is observed. The theoretical intrinsic magnetic noise floor of such sensors reaches a minimum value of 35 pT/Hz. This approach shows a magnetic field sensitivity of ∼5 Hz/mT in a bias magnetic field of up to 120 mT. Such sensors have the potential in applications required for enhanced dynamic sensitivity in high-field magnetometry.

Dynamics of the stress-mediated magnetoelectric memory cell N×(TbCo2/FeCo)/PMN-PT

Stress-mediated magnetoelectric heterostructures represent a very promising approach for the realization of ultra-low energy Random Access Memories. The magnetoelectric writing of information has been extensively studied in the past, but it was demonstrated only recently that the magnetoelectric effect can also provide means for reading the stored information. We hereby theoretically study the dynamic behaviour of a magnetoelectric random access memory cell (MELRAM) typically composed of a magnetostrictive multilayer N×(TbCo2/FeCo) that is elastically coupled with a 〈011〉 PMN-PT ferroelectric crystal and placed in a Wheatstone bridge-like configuration. The numerical resolution of the LLG and electrodynamics equation system demonstrates high speed write and read operations with an associated extra-low energy consumption. In this model, the reading energy for a 50 nm cell size is estimated to be less than 5 aJ/bit.

Voltage-Driven 180° Magnetization Switching in Magnetoelectric Heterostructures

Voltage-driven non-volatile 180° magnetization switching without electric current provides an energy efficiency alternative to current-driven spintronics. Here, by using the finite-element method (FEM) which combined the Landau–Lifshitz–Gilbert micromagnetics with elastodynamic and electrostatics, we numerically demonstrate the application of the strain-mediated magnetoelectric (ME) effect for voltage control magnetization switching in ME heterostructures (e.g., a heterostructure consisting of a square-shaped nickel nano-magnet on top of the piezoelectric island with two pairs of electrodes around the nano-magnet element). This full 180° magnetization switching with voltage is applied by utilizing both the in-plane piezostrains and magnetic-shaped anisotropy of ME heterostructures. FEM simulation results clearly demonstrate that the magnetization in the nano-magnet can be switched unidirectionally to complete a 180° magnetization under two sets of voltage pulse. These results provide useful information for the design of low-power and fast voltage controlled spintronics.

Temperature Dependence of the Resonant Magnetoelectric Effect in Layered Heterostructures.

The dependence of the resonant direct magnetoelectric effect on temperature is studied experimentally in planar composite structures. Samples of rectangular shapes with dimensions of 5 mm × 20 mm employed ferromagnetic layers of either an amorphous (metallic glass) alloy or nickel with a thickness of 20–200 μm and piezoelectric layers of single crystalline langatate material or lead zirconate titanate piezoelectric ceramics with a thickness of 500 μm. The temperature of the samples was varied in a range between 120 and 390 K by blowing a gaseous nitrogen stream around them. It is shown that the effective characteristics of the magnetoelectric effect—such as the mechanical resonance frequency fr, the quality factor Q and the magnitude of the magnetoelectric coefficient αE at the resonance frequency—are contingent on temperature. The interrelations between the temperature changes of the characteristics of the magnetoelectric effect and the temperature variations of the following material parameters—Young’s modulus Y, the acoustic quality factor of individual layers, the dielectric constant ε, the piezoelectric modulus d of the piezoelectric layer as well as the piezomagnetic coefficients λ(n) of the ferromagnetic layer—are established. The effect of temperature on the characteristics of the nonlinear magnetoelectric effect is observed for the first time. The results can be useful for designing magnetoelectric heterostructures with specified temperature characteristics, in particular, for the development of thermally stabilized magnetoelectric devices.

Multilayered ceramic heterostructures of lead zirconate titanate and nickel-zinc ferrite for magnetoelectric sensor elements

The preparation method of magnetoelectric multilayered ceramic heterostructures was suggested, and series of the rectangular and disk shape samples were produced on the base of this method. The maximum value of a magnetoelectric voltage coefficient αE=35V/(cm×Oe) was observed for the eleven-layered rectangular specimen at the electromechanical resonance frequency fr=144kHz, НDC=84Oe, and НAC=2.5 Oe. The sensitivity to static magnetic fields is equal to 3.5×10−2Oe, and the alternating field sensitivity is equal to 8×10−3Oe.

A flexible, high-performance magnetoelectric heterostructure of (001) oriented Pb(Zr0.52Ti0.48)O3film grown on Ni foil

In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by depositing a (001) oriented Pb(Zr0.52Ti0.48)O3 (PZT) film on a thin, flexible Ni foil buffered with LaNiO3/HfO2. Excellent ferroelectric properties and large ME voltage coefficient of 3.2 V/cm⋅Oe were realized from the PZT/Ni heterostructure. The PZT/Ni composite’s high performance was attributed to strong texturing of the PZT film, coupled with the compressive stress in the piezoelectric film. Besides, reduced substrate clamping in the PZT film due to the film on the foil structure and strong interfacial bonding in the PZT/LaNiO3/HfO2/Ni heterostructure could also have contributed to the high ME performance of PZT/Ni.

Nonvolatile control of transport and magnetic properties in magnetoelectric heterostructures by electric field**Project supported by the National Natural Science Foundation of China (Grant No. 51571108).

Nonvolatile manipulation of transport and magnetic properties by external electric field is significant for information storage. In this study, we investigate the electric field control of resistance and magnetization in a magnetoelectric heterostructure comprising an electronic phase-separated La0.325Pr0.3Ca0.375MnO3 (LPCMO) thin film and a ferroelectric (011)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) substrate. In a room-temperature poled sample, the metal-to-insulator transition temperature of an LPCMO film increases and the resistance decreases with variation in the effect of the remnant strain. Meanwhile, the increase in the magnetization of the sample is observed as well. This effect would be beneficial for the development of novel storage devices with low power consumption.

Long-range Stripe Nanodomains in Epitaxial (110) BiFeO3 Thin Films on (100) NdGaO3 Substrate

Here, we report the observation of ferroelectric and ferroelastic nanodomains in (110)-oriented BiFeO3 (BFO) thin films epitaxially grown on low symmetric (100) NdGaO3 (NGO) substrate. We observed long range ordering of ferroelectric 109° stripe nanodomains separated by periodic vertical domain walls in as-grown 130 nm thick BFO films. The effect of La0.67Sr0.33CoO3 (LSCO) conducting interlayer on domain configurations in BFO/NGO film was also observed with relatively short range-ordering of stripe domains due to the modified electrostatic boundary conditions in BFO/LSCO/NGO film. Additional studies on B-site doping of Nb ions in BFO films showed change in the domain structures due to doping induced change in lattice anisotropy while maintaining the stripe domain morphology with 109° domain wall. This long-range array of ferroelectric and ferroelastic domains can be useful for optoelectronic devices and ferroelastic templates for strain coupled artificial magnetoelectric heterostructures.

On the speed of piezostrain-mediated voltage-driven perpendicular magnetization reversal: a computational elastodynamics-micromagnetic phase-field study

By linking the dynamics of local piezostrain to the dynamics of local magnetization, we computationally analyzed the speed of a recently proposed scheme of piezostrain-mediated perpendicular magnetization reversal driven by a voltage pulse in magnetoelectric heterostructures. We used a model heterostructure consisting of an elliptical ultrathin amorphous Co20Fe60B20 on top of a polycrystalline Pb(Zr,Ti)O3 (PZT) thin film. We constructed a diagram showing the speed of perpendicular magnetization reversal as a function of the amplitude of the applied voltage pulse and the stiffness damping coefficient of PZT film. In addition, we investigated the influence of thermal fluctuations on the switching speed. The analyses suggest that the switching time remains well below 10 ns and that the energy dissipation per switching is on the order of femtojoule. The present computational analyses can be generally used to predict the speed of piezostrain-enabled magnetization switching and magnetic domain-wall motion, which critically determines the response time of corresponding piezostrain-enabled spintronic and magnonic devices.

Metallic Glass/PVDF Magnetoelectric Laminates for Resonant Sensors and Actuators: A Review.

Among magnetoelectric (ME) heterostructures, ME laminates of the type Metglas-like/PVDF (magnetostrictive+piezoelectric constituents) have shown the highest induced ME voltages, usually detected at the magnetoelastic resonance of the magnetostrictive constituent. This ME coupling happens because of the high cross-correlation coupling between magnetostrictive and piezoelectric material, and is usually associated with a promising application scenario for sensors or actuators. In this work we detail the basis of the operation of such devices, as well as some arising questions (as size effects) concerning their best performance. Also, some examples of their use as very sensitive magnetic fields sensors or innovative energy harvesting devices will be reviewed. At the end, the challenges, future perspectives and technical difficulties that will determine the success of ME composites for sensor applications are discussed.

Understanding and designing magnetoelectric heterostructures guided by computation: progresses, remaining questions, and perspectives

Magnetoelectric composites and heterostructures integrate magnetic and dielectric materials to produce new functionalities, e.g., magnetoelectric responses that are absent in each of the constituent materials but emerge through the coupling between magnetic order in the magnetic material and electric order in the dielectric material. The magnetoelectric coupling in these composites and heterostructures is typically achieved through the exchange of magnetic, electric, or/and elastic energy across the interfaces between the different constituent materials, and the coupling effect is measured by the degree of conversion between magnetic and electric energy in the absence of an electric current. The strength of magnetoelectric coupling can be tailored by choosing suited materials for each constituent and by geometrical and microstructural designs. In this article, we discuss recent progresses on the understanding of magnetoelectric coupling mechanisms and the design of magnetoelectric heterostructures guided by theory and computation. We outline a number of unsolved issues concerning magnetoelectric heterostructures. We compile a relatively comprehensive experimental dataset on the magnetoelecric coupling coefficients in both bulk and thin-film magnetoelectric composites and offer a perspective on the data-driven computational design of magnetoelectric composites at the mesoscale microstructure level.

Nonvolatile transtance change random access memory based on magnetoelectric P(VDF-TrFE)/Metglas heterostructures

Transtance change random access memory (TCRAM) is a type of nonvolatile memory based on the nonlinear magnetoelectric coupling effects of multiferroics. In this work, ferroelectric P(VDF-TrFE) thin films were prepared on Metglas foil substrates by the sol-gel technique to form multiferroic heterostructures. The magnetoelectric voltage coefficient of the heterostructure can be switched reproducibly to different levels between positive and negative values by applying selective electric-field pulses. Compared with bulk multiferroic heterostructures, the polarization switching voltage was reduced to 7 V. Our facile technological approach enables this organic magnetoelectric heterostructure as a promising candidate for the applications in multilevel TCRAM devices.

Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature.

The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.