Magnetoelectric Materials Research Articles

Soft Matter Mechanics and the Mechanisms Underpinning the Infrared Vision of Snakes

Summary Pit-bearing snakes (vipers, pythons, and boas) have the extraordinary ability to “see” and accurately locate their prey and predators in total darkness. These animals use the infrared radiation emanating from objects that are warmer relative to the background environment to form a thermal image. Although enormous progress has been made to identify the key physiological features that enable the infrared vision of these snakes and a few other animals, the precise thermoelectric transduction mechanism that mediates the conversion of infrared heat to processable electrical signals has remained elusive. In this work, we quantitatively outline how cells in the snake's pit membrane organ act as apparent pyroelectric materials and convert infrared radiation into electrical signals. Despite the exceptional simplicity of our proposed mechanism and model, we are able to explain many central experimental results pertaining to the transduction process.

Modeling of electromagnetic radiation-induced from a magnetostrictive/piezoelectric laminated composite

Magnetoelectric (ME) materials can realize the conversions between electric and magnetic energy. Different from the previous studies, the electromagnetic (EM) radiation of ME materials has been adequately considered in this work. The electrical energy input can be converted into the dynamic magnetization oscillation by converse magnetoelectric (CME) effect. The antennas operate at their acoustic resonance frequency, which provides a new idea for antenna miniaturization. We analyze the CME effect and EM radiation from a vibrating ME laminated composite. The results show that the ME heterostructure resembles an ideal magnetic dipole in terms of radiating EM waves. This structure reduces the antenna size by several orders of magnitude, suggesting vast superiority of controlling magnetizations to generate EM radiation at a micro-scale.

Progress in multiferroic and magnetoelectric materials: applications, opportunities and challenges

The development of electronic technology is flexibly related to the progresses made in material science. Functional materials out of the broad class of materials available today offer unique chance for developing novel components and devices. In this framework, provides a new class of functional materials, the multiferroics (MFs), combine two or more different ferroic orders (viz. ferroelectric, ferromagnetic and ferroelastic) in a single phase and are utilized in a broad range of systems. In connection with multiferroism, a broad category of materials namely magnetoelectrics allow the electric control on magnetization or vice-versa are explored extensively. Even though, the research in the field of MFs and magnetoelectric (ME) materials can be traced back to revolutionary research in the early 1950s. There has been a contemporary resurgence of concern motivation by long-term technological aspirations. The center of attention of this review is on elementary understanding of the MFs and ME materials using a multidisciplinary approach to address the underlying mechanism responsible for the coupling, their applications in some novel devices, new opportunities and future challenges.

Magnetoelectric Studies of Close-Packed and Hierarchically Ordered CoFe2O4/Pb(Zr0.52Ti0.48)O3/La0.6Sr0.4MnO3/LaNiO3 Multiferroic Thin Films

Enhanced magnetoelectric effects in two-dimensional multiferroics promise greater interests for fundamental understanding and for device applications. To ameliorate properties and multifunctionality of magnetoelectric materials, highly ordered multiferroic thin films ought to be optimally designed with a high surface area and with a minimum contact area between the substrate and the films. Fabrication of hierarchically ordered, hemispherical close-packed free-standing multiferroic thin film structures of CoFe2O4 (CFO)/Pb(Zr0.52Ti0.48)O3 (PZT)/La0.6Sr0.4MnO3 (LSMO)/LaNiO3 (LNO) on a Pt/Ti/SiO2/Si substrate using a RF magnetron sputtering technique is reported here. The hemispherical space inside the shell structures, inherited from the spherical polymer, are shown by the cross-sectional scanning transmission electron microscopy. Importantly, the observed enhancement of remanent polarization is elucidated based on the facts, like the generation of a high level of compressive stress, a large thermal expansion coefficient of LSMO, and a minimal lattice mismatch with the PZT thin film.

Magnetoelectric effect arising from a field-induced pseudo Jahn-Teller distortion in a rare-earth magnet

Magnetoelectric materials are attractive for several applications, including actuators, switches, and magnetic field sensors. Typical mechanisms for achieving a strong magnetoelectric coupling are rooted in transition metal magnetism. In sharp contrast, here we identify $\mathrm{CsEr}{({\mathrm{MoO}}_{4})}_{2}$ as a magnetoelectric material without magnetic transition metal ions, thus ensuring that the Er ions play a key role in achieving this interesting property. Our detailed study includes measurements of the structural, magnetic, and magnetoelectric properties of this material. Bulk characterization and neutron powder diffraction show no evidence for structural phase transitions down to 0.3 K and therefore $\mathrm{CsEr}{({\mathrm{MoO}}_{4})}_{2}$ maintains the room temperature $P2/c$ space group over a wide temperature range without external magnetic field. These same measurements also identify collinear antiferromagnetic ordering of the ${\mathrm{Er}}^{3+}$ moments below ${T}_{N}=0.87\phantom{\rule{4pt}{0ex}}\mathrm{K}$. Complementary dielectric constant and pyroelectric current measurements reveal that a ferroelectric phase with a maximum polarization $P\ensuremath{\sim}0.6\phantom{\rule{4pt}{0ex}}\mathrm{nC}/{\mathrm{cm}}^{2}$ emerges when applying a modest external magnetic field, which indicates that this material has a strong magnetoelectric coupling. We argue that the magnetoelectric coupling in this system arises from a pseudo Jahn-Teller distortion induced by the magnetic field.

Electrochemical approaches to room temperature magnetoelectric materials

Electrochemical voltage control of magnetism is an emerging approach for energy-efficient magnetoelectric materials. In contrast to conventional magnetoelectric concepts, which are typically restricted to low temperatures, low magnetization, or complex heterostructures, electrochemical routines can be efficiently applied to magnetic oxides and metals with high magnetization at room temperature. Potential-induced faradaic reactions, such as interfacial oxidation/reduction, electrochemical hydrogenation, and ion intercalation are used to set different magnetic states at the interface and beyond. Recent advances include the reversible, redox-based ON/OFF switching of magnetization and change of the exchange bias in metal oxide/metal nanostructures, and the fast spin reorientation upon hydrogenation of Pd/Co films. The modulations can be nonvolatile and open a path toward voltage-reprogrammable magnets for spintronics, actuation and sensor applications. • Electrochemistry is a route to room temperature magnetoelectric metals and oxides. • Redox reactions and ion intercalation tune magnetism at the interface and beyond. • Advances in the magneto-ionic mechanism involve oxygen, hydrogen, and lithium ions. • Oxygen-based redox reactions control complex magnetic phenomena in metal films. • Electrochemical hydrogenation offers fast magneto-ionic switching.

Magnetoelectrics: Three Centuries of Research Heading towards the 4.0 Industrial Revolution.

Magnetoelectric (ME) materials composed of magnetostrictive and piezoelectric phases have been the subject of decades of research due to their versatility and unique capability to couple the magnetic and electric properties of the matter. While these materials are often studied from a fundamental point of view, the 4.0 revolution (automation of traditional manufacturing and industrial practices, using modern smart technology) and the Internet of Things (IoT) context allows the perfect conditions for this type of materials being effectively/finally implemented in a variety of advanced applications. This review starts in the era of Rontgen and Curie and ends up in the present day, highlighting challenges/directions for the time to come. The main materials, configurations, ME coefficients, and processing techniques are reported.

Electric Field Control of Magnetic Permeability in Co-Fired Laminate Magnetoelectric Composites: A Phase-Field Study for Voltage Tunable Inductor Applications.

Control of magnetic permeability through electric field in magnetoelectric materials promises to create novel voltage tunable inductors (VTIs). VTIs synthesized using co-fired ceramic processing exhibit many advantages over traditional epoxy bonding method, but the internal residual stress in co-fired VTIs resulting from thermal expansion mismatch hinders a full exploitation of the tunability of permeability. To find the optimal condition for high tunability of co-fired VTIs, domain-level phase field modeling and computer simulation are employed to study co-fired magnetoelectric composites comprising NiZn ferrite and PZT. Two key factors important toward increasing the inductor tunability are systematically investigated: intrinsic magnetocrystalline anisotropy of the ferrite material and internal residual stress caused by the co-firing process. The simulations indicate that in order to achieve a large tunability, the tuned permeability should be confined within the linear region of the reciprocal of susceptibility and stress. Additionally, both magnetocrystalline anisotropy and residual stress should be as small as possible. These results provide a design strategy for realizing high-tunability co-fired VTIs.

Scanning probe microscopy study of cobalt ferrite-barium titanate coreshell magnetoelectric nanoparticles

Cobalt ferrite – barium titanate coreshell composite nanoparticles are an important part of the emerging field of magnetoelectric materials. Understanding the structure of these nanoparticles is vital towards controlling and adjusting their key properties for specific applications. Although transmission electron microscopy can reveal nanoparticle size, shape, and crystallinity, key information regarding the magnetic properties and the compositional makeup of the coreshell configuration remains elusive at nanoscale. This paper covers the use of scanning probe microscopy to directly measure these features using topography imaging, magnetic force imaging, and phase imaging. This technique provides significant insights into the intrinsic magnetoelectric coupling between the magnetostrictive cobalt ferrite core and the piezoelectric barium titanate shell. Particularly, this technique was applied to obtain phase images that directly exhibited the coreshell configuration, including an intermediate transition region between the core and the shell. The samples examined include 20 nm and 50 nm cobalt ferrite-barium titanate coreshell nanoparticles fabricated via co-precipitation and sol–gel synthesis. The results revealed a cuboid shape for the cobalt ferrite cores, and an oval shape for the cobalt ferrite-barium titanate coreshell nanoparticles. This result was confirmed by transmission electron microscopy. Additionally, the paper comprehensively analyzes the samples in their powder form via X-ray diffraction. The results indicate that the crystallinity of barium titanate is enhanced as the cobalt ferrite concentration is increased because of heterogeneous nucleation requiring a lower nucleation barrier compared to homogeneous nucleation.

Remarkable magnetoelectric effect in single crystals of honeycomb magnet Mn4Nb2O9

Linear magnetoelectrics refer to those compounds in which ferroelectric (FE) polarization can be generated by applying the magnetic field. This scenario opens an additional avenue toward high-temperature magnetoelectric (ME) coupling that is achievable in a large class of relatively weak frustrated magnetic systems such as honeycomb antiferromagnets. It is, thus, urgent to unveil the physics underlying the linear ME coupling in these linear ME materials. We grow the single crystals of Mn4Nb2O9, a linear ME candidate with high magnetic ordering temperature, and carry out a set of structural, magnetic, and ME characterizations. An antiferromagnetic ordering with [001]-oriented moments at the Neel point TN = 109 K is identified together with magnetic field driven large electric polarization emerging at TN, due to the strong exchange striction dependent mechanism. The measured ME coupling tensor α fits well the magnetic symmetry −3′m′, consistent with the linear ME scenario. Furthermore, remarkable responses of FE polarization and magnetization to the magnetic field and electric field, respectively, are demonstrated.

Interface assisted strain-induced magnetoelectric coupling in core-shell nanostructures of CoFe2O4 @ZnO

Artificially engineered magnetoelectric materials, whose electrical properties can be manipulated by an external magnetic field and vice versa are a new class of materials and find extensive applications in the field of emerging technologies like sensors, electrically controlled spintronic, and microelectronics and memory storage devices. Composites, having ferromagnetic and ferroelectric components are commonly employed where coupling between magnetic and electric fields is relatively weak. It is known that the interface between the components plays a very crucial role for achieving a stronger magnetoelectric (ME) coupling in artificially engineered magnetoelectric materials if the composites are synthesized with a ferro/ferri magnetic core and a ferro/piezoelectric shell. Such core-shell architecture ensures strong interaction and enables better connectivity. In realizing this goal, we report a simple technique to fabricate a core-shell nanostructure consisting of a ferrimagnetic core of CoFe2O4 and a piezoelectric shell of ZnO. The core size is varied and the elastic strain mediated magnetoelectric coupling mechanism through the interface of the core-shell nanostructure is examined.

Optical response of a topological-insulator–quantum-dot hybrid interacting with a probe electric field

We study the interaction between a topological insulator nanoparticle and a quantum dot subject to an applied electric field. The electromagnetic response of the topological insulator is derived from axion electrodynamics in the quasistatic approximation. Localized modes are quantized in terms of dipolar bosonic modes, which couples dipolarly to the quantum dot. Hence, we treat the hybrid as a two-level system interacting with a single bosonic mode, where the coupling strength encodes the information concerning the nontrivial topology of the nanoparticle. The interaction of the hybrid with the environment is implemented through the coupling with a continuum reservoir of radiative output modes and a reservoir of phonon modes. In particular, we use the method of Zubarev's Green functions to derive an expression for the optical absorption spectrum of the system. We apply our results to a realistic system which consists of a topological insulator nanoparticle made of TlBiSe$_{2}$ interacting with a cadmium selenide quantum dot, both immersed in a polymer layer such as poly(methyl methacrylate). The optical absorption spectrum exhibits Fano resonances with a line shape that strongly depends on the polarization of the electric field as well as on the topological magnetoelectric polarizability $\theta$. Our results and methods can also be applied to nontopological magnetoelectric materials such as Cr$_{2}$O$_{3}$.

Antisite disorder driven magnetodielectric and magnetocaloric effect in double perovskite La2−xSrxCoMnO6 (x = 0.0, 0.5, 1.0)

We report magnetic, dielectric, magnetodielectric, and magnetocaloric responses of La2CoMnO6 (LCMO) and Sr doped La2−xSrxCoMnO6 (x = 0.5 and 1.0) induced by antisite disorder. The antisite disorder is enhanced with Sr-doping at La-sites. Co ions have mixed valence states on Sr-doping, with Co3+ and Co2+. Mn is present in mixed valence of Mn4+ and Mn3+ states with Sr doping. The dielectric constant of Sr doped LCMO was found to increase, whereas the magnetodielectric coupling was found suppressed due to the increase of antisite disorder. The magnetic field-dependent magnetodielectric effect clearly shows M2 behavior for all the samples in the field range of 0 to ±6 T in their respective ferroic phases. All the samples show spin glass like ordering in the ground state. We also report the magnetic entropy change in magnetoelectric material La2−xSrxCoMnO6 (x = 0, 1.0) samples. The change in magnetic entropy ΔSm originates mainly from the combined effect of the ferromagnetic/antiferromagnetic interaction and the magnetodielectric effect in La2−xSrxCoMnO6 (x = 0, 1.0). The observed value of the magnetocaloric effect (1.2 J/kg K) for x = 1.0 is likely to originate from the antisite disordered phases near Curie temperature.

Intrinsic role of ↑↑↓↓-type magnetic structure on magnetoelectric coupling in Y2NiMnO6

Structure-property correlations are a major challenge in the investigation of magnetoelectric multiferroic materials. We have systematically investigated the intrinsic role of ↑↑↓↓-type order in magnetoelectric coupling in Y2NiMnO6. The calculated results reveal that the ferromagnetic (FM) order is the magnetic structure of the ground state and the total energy of ↑↑↓↓-type order is close to that of the FM order. The electric polarization is calculated to be 0.78 μC/cm2 along the crystallographic b-axis for UNi = UMn = 3 eV. In addition to the exchange-striction mechanism, a more noticeable contribution from redistribution of polarized charge is found in our study. Magnetic hysteresis loops show the ferromagnetism in Y2NiMnO6, which can be explained by magnetic field-induced spin flop transition from the E-type to FM order. Our DFT + U theoretical investigations also proposed a switching adiabatic path of magnetoelectric coupling, in which the 180° reverse of electric polarization is driven by rotation of spins.

Magnetoelectric Materials for Miniature, Wireless Neural Stimulation at Therapeutic Frequencies

A major challenge for miniature bioelectronics is wireless power delivery deep inside the body. Electromagnetic or ultrasound waves suffer from absorption and impedance mismatches at biological interfaces. On the other hand, magnetic fields do not suffer these losses, which has led to magnetically powered bioelectronic implants based on induction or magnetothermal effects. However, these approaches have yet to produce a miniature stimulator that operates at clinically relevant high frequencies. Here, we show that an alternative wireless power method based on magnetoelectric (ME) materials enables miniature magnetically powered neural stimulators that operate up to clinically relevant frequencies in excess of 100Hz. We demonstrate that wireless ME stimulators provide therapeutic deep brain stimulation in a freely moving rodent model for Parkinson's disease and that these devices can be miniaturized to millimeter-scale and fully implanted. These results suggest that ME materials are an excellent candidate to enable miniature bioelectronics for clinical and research applications.

Concepts from the linear magnetoelectric effect that might be useful for antiferromagnetic spintronics

We discuss the correspondence between the current-induced spin polarization in non-centrosymmetric magnetic metals and the linear magnetoelectric effect in non-centrosymmetric magnetic insulators using a linear-response theory and the concept of magnetoelectric multipoles. We show that the magnetoelectric toroidal moment is a particularly useful quantity since it determines the ground-state antiferromagnetic domain of a non-centrosymmetric antiferromagnet in the presence of a steady-state electric current. We analyze two prototypical antiferromagnetic spintronic materials—Mn2Au and CuMnAs—and show that the experimentally reported domain reorientations are consistent with the alignment of their toroidal moments parallel to the applied electric current. Finally, we determine whether similar behavior should be expected in the prototypical insulating magnetoelectric materials, Cr2O3 and LiMPO4, if they could be doped into a semiconducting or metallic regime.

Interplay of 4f−3d interactions and spin-induced ferroelectricity in the green phase Gd2BaCuO5

In most of the spin-induced multiferroics, the ferroelectricity is caused by inversion symmetry breaking by complex spin structures of the transition-metal ions. Here, we report the importance of interplay of 4 f − 3 d magnetic interactions in inducing ferroelectricity in the centrosymmetric (Pnma) green phase compound G d 2 BaCu O 5 . With decreasing temperature, a long-range incommensurate ordering of both G d 3 + and C u 2 + spins at T N = 11.8 K occurs with the modulation vector k = ( 0 , 0 , g ) and a lock-in transition to a strongly noncollinear structure with k c = ( 0 , 0 , ½ ) at T loc ∼ 6 K . Both spin structures induce electric polarization consistent with the polar magnetic space groups P m 1 ′ ( α , 0 , g ) s s and P a c a 2 1 , respectively. Based on the symmetry analysis of magnetoelectric interactions, we suggest that the ferroelectricity in both commensurate and incommensurate phases is driven by a complex interplay of two-spins and single-spin contributions from magnetic ions located in noncentrosymmetric environments. Our study demonstrates that the green phase family of compounds may serve as a playground for studying the multiferroic phenomena, where the interplay of 4 f − 3 d interactions demonstrates an alternative route to find magnetoelectric materials.

Trompe L\u2019oeil Ferromagnetism

The characteristics of ferro-(ferri)magnetism with non-zero magnetization include magnetic attraction, magnetic circular dichroism, and magneto-optical Kerr (MOKE), Faraday, and various anomalous Hall-type (Hall, Ettingshausen, Nernst, and thermal Hall) effects. Non-magnetic or antiferromagnetic materials in external electric fields or other environments (called specimen constituents) can share symmetry operational similarity (SOS) with magnetization (boldsymbol{mathcal{M}}) in relation to broken symmetries. These specimen constituents can be associated with non-zero magnetization and/or show ferromagnetism-like behaviors, so we say that they exhibit Trompe L’oeil Ferromagnetism. Examples include linear magnetoelectric materials such as Cr2O3 under electric fields, Faraday effect in chiral materials such as tellurium with current flow, magnetic field induced by the motion of Neel- or Bloch-type ferroelectric walls, and magneto-optical Kerr (MOKE), Faraday effect, and/or anomalous Hall-type effects in certain antiferromagnets such as Cr2O3, MnPSe3, Mn4(Nb,Ta)2O9, and Mn3(Sn,Ge,Ga). A large number of new specimen constitutes having SOS with boldsymbol{mathcal{M}} are proposed, and require future experimental verification of their ferromagnetism-like behaviors, and also theoretical understanding of possible microscopic mechanisms.

Optical intersubband properties of a core–shell semiconductor–topological insulator quantum dot described by θ-electrodynamics

The optical properties of a spherical topological insulator embedded concentrically in a single-electron system consisting of a core-shell GaAs quantum dot are analyzed, when the system is under a uniform external magnetic field. The topological insulator's magnetoelectric response is computed in the effective framework of $\theta$-electrodynamics, which allows analytical calculations for the induced electric and magnetic potentials by Green's Function method. The GaAs Hamiltonian is constructed in the effective-mass approximation, and its corresponding Schr\"odinger equation is numerically solved through the Lagrange-mesh method. We compute the total absorption coefficients and refractive index changes given by the non-linear iterative density matrix formalism up to third order. Our results show that the presence of the magnetoelectric material causes new dipolar transitions otherwise not allowed. Also, an enhancement of the photon absorption is found when the incident light polarization is oriented parallel to the external magnetic field, in comparison with perpendicular polarization. Moreover, we report an appreciable blue shift in the optical functions when the values of the $\theta$-parameter are increased. These results can be useful for indirect experimental measures of the magnetoelectric polarizability which is proportional to the QED fine-structure constant $\alpha$.

Magneto-electric coupling and transport properties of LaFeO3–Pb(Zr0.58Ti0.42)O3–organic poly(vinylidene fluoride) nanocomposite

The magneto-electric material of LaFeO3–Pb(Zr0.58Ti0.42)O–poly(vinylidene fluoride) has been prepared by a chemical “pyrophoric reaction technique” and followed by “solid state route”. The formation of LaFeO3, Pb(Zr0.58Ti0.42)O3 and poly(vinylidene fluoride) phases is confirmed by X-ray diffraction technique. The magneto-electric coupling and electrical response have been carried out at room temperature (300 K). The prepared composite reveals the strain mediated magnetoelectric effect at room temperature with longitudinal and transverse configurations at lower frequency region under an external magnetic field. The impedance spectroscopy is used to study the complex electrical modulus and electrical transport properties of the prepared composites at room temperature. The complex modulus and impedance spectra study also helps to understand the mechanism of the electrical transport process, which depicts a non-Debye type of conduction mechanism of the system.