Giant Magnetoelectric Coupling Research Articles

Magnetoelectric and MIESST effects in spin crossover materials exhibiting symmetry-breaking.

Giant magnetoelectric coupling and magnetic-field-induced spin state trapping (MIESST) were recently reported in spin crossover materials with polar phases. We discuss these phenomena considering the distinct contributions of the change of the molecular spin state, driven by the magnetic field, and the coupled structural symmetry-breaking during the stepwise change of electric polarisation or MIESST.

In a search for effective giant magnetoelectric coupling: Magnetically induced elastic resonance in Ni-Mn-Ga/P(VDF-TrFE) composites

Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) is a piezoelectric polymer suitable for applications in electromechanical and magnetoelectric (ME) systems. Ni-Mn-Ga alloys exhibit a giant magnetoelastic response related to their structural transformations of martensitic type, accompanied by noticeable volume changes. Together, in a thin film composite containing an ensemble of Ni-Mn-Ga particles (10 wt.%) distributed in the P(VDF-TrFE) piezopolymer, they ensure an unprecedented resonance amplification of the ME effect. Thus, a giant value of ME coefficient of 6.05 V·cm−1· Oe−1 under AC magnetic drive field of 0.2 Oe and DC bias field of 1300 Oe is experimentally observed and discussed. The physical mechanism of the proposed ME response amplification has been explained theoretically through the volume magnetostriction of the magnetostrictive particles and resonant elastic oscillation of the piezoelectric polymer matrix.

In situ formation of composite thin film with (111) oriented Ni0.5Zn0.5Fe2O4 pillar array surrounded by BaTiO3 for ferroelectric-ferromagnetic coupling

For a new breakthrough of highly efficient magnetoelectric (ME) coupling of multiferroic composite thin film in application of next generation multifunctional devices, it is important to control constituent magnetic phase pillar array independently embedded inside piezoelectric phase. In this work, in situ spin-coated xNi0.5Zn0.5Fe2O4/(1-x)BaTiO3 composite thin films on Si substrate with high magnetoelectric coupling are successfully obtained via phase separation. Results show that hexagonal Ni0.5Zn0.5Fe2O4 (NZFO) grain grows (111)-oriented as single crystal pillars arrayed independently uniformly and surrounded by BaTiO3 (BTO) phase. Ti and Fe ions are doped into the NZFO and BTO phases respectively and decreased with the decrease in corresponding constituent phases. Grain size and lattice constant of the cubic NZFO are from ~1 to ~0.5 μm and from 0.8383 nm to 0.8369 nm respectively in terms of x. The orientation degree of thin films is> 56% when x is above 0.8. The 0.8NZFO/0.2BTO thin film with and without pure BTO after-spincoated shows giant ME coupling effect, about 40% change of magnetization of NZFO in terms of phase transition of ferroelectric BTO at Curie temperature ~398 K. It is much larger than others on Si substrate ever reported and may be applied cost-effectively, coupling-efficiently and widely in Si-based chips area.

Significant improving magnetoelectric sensors performance based on optimized magnetoelectric composites via heat treatment

Laminated magnetoelectric (ME) composites consisting of magnetostrictive and piezoelectric materials have been investigated and proved to realize strong ME coupling, which shows great benefits to fabricate high sensitivity ME magnetic sensors. In this work, optimized L–T mode ME composites consisting of heat-treated Metglas ribbons and [110]-oriented Mn-doped 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (Mn-doped PMN-PT) single crystal fibers were reported, which achieves giant ME coupling and ultrahigh ME electric field coefficient of 4.26 × 104 V cm−1 Oe−1 at the electromechanical resonance. The equivalent magnetic noise of the ME sensor based on the proposed ME composites is only 2.89 fT Hz−1/2 at the electromechanical resonance, which exhibits great prospect in the application of precision magnetic field detection. Based on the characterization of heat-treated Metglas samples and the finite element simulation of the ME composites, the improved performance of the ME composites and ME sensors can be attributed to the enhanced properties of heat-treated Metglas (higher piezomagnetic coefficient d 33,m, higher induced magnetic flux density and lower mechanical loss) due to the enhancement of nanocrystallization and the stronger magnetic flux concentration effect corresponding to the dimension of the Metglas ribbons.

Strain-Mediated Giant Magnetoelectric Coupling in a Crystalline Multiferroic Heterostructure.

Multiferroic heterostructures based on the strain-mediated mechanism present ultralow heat dissipation and large magnetoelectric coupling coefficient, two conditions that require endless improvement for the design of fast nonvolatile random access memories with reduced power consumption. This work shows that a structure consisting of a [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (001) substrate on which a crystalline FeGa(001)/MgO(001) bilayer is deposited exhibits a giant magnetoelectric coupling coefficient of order 15 × 10–6 s m–1 at room temperature. That result is a 2-fold increment over the previous highest value. The spatial orientation of the magnetization vector in the epitaxial FeGa film is switched 90° with the application of electric field. The symmetry of the magnetic anisotropy is studied by the angular dependence of the remanent magnetization, demonstrating that poling the sample generates a switchable uniaxial magnetoelastic anisotropy in the film that overcomes the native low 4-fold magnetocrystalline anisotropy energy. Magnetic force microscopy shows that the switch of the easy axis activates the displacement of domain walls and the domain structures remain stable after that point. This result highlights the interest in single-crystalline structures including materials with large magnetoelastic coupling and small magnetocrystalline anisotropy for low-energy-consuming spintronic applications.

Giant Magnetoelectric Coupling and Magnetic-Field-Induced Permanent Switching in a Spin Crossover Mn(III) Complex.

We investigate giant magnetoelectric coupling at a Mn3+ spin crossover in [MnIIIL]BPh4 (L = (3,5-diBr-sal)2323) with a field-induced permanent switching of the structural, electric, and magnetic properties. An applied magnetic field induces a first-order phase transition from a high spin/low spin (HS-LS) ordered phase to a HS-only phase at 87.5 K that remains after the field is removed. We observe this unusual effect for DC magnetic fields as low as 8.7 T. The spin-state switching driven by the magnetic field in the bistable molecular material is accompanied by a change in electric polarization amplitude and direction due to a symmetry-breaking phase transition between polar space groups. The magnetoelectric coupling occurs due to a γη2 coupling between the order parameter γ related to the spin-state bistability and the symmetry-breaking order parameter η responsible for the change of symmetry between polar structural phases. We also observe conductivity occurring during the spin crossover and evaluate the possibility that it results from conducting phase boundaries. We perform ab initio calculations to understand the origin of the electric polarization change as well as the conductivity during the spin crossover. Thus, we demonstrate a giant magnetoelectric effect with a field-induced electric polarization change that is 1/10 of the record for any material.

Low-power eddy current detection with 1-1 type magnetoelectric sensor for pipeline cracks monitoring

Pipeline systems, such as oil and natural gas pipelines, which are normally buried underground or distributed under the sea, are susceptible to corrosion and pressure destruction, and hence timely and reliable nondestructive testing (NDT) is necessary. Conventional nondestructive testing methods are generally based on ultrasonic, eddy current and magnetic flux leakage mechanism. With respect to eddy current testing (ECT) technologies, the current challenge is to develop magnetic sensors with high detection ability, extremely low power consumption and compatible with Internet of Things (IoT). Giant resonant magnetoelectric (ME) coupling has been previously reported in our proposed 1-1 ME composites. Here, we further presented an investigation on the eddy current testing (ECT) using 1-1 type ME sensor. The proposed ECT probe was built by integrating a small exciting coil surrounding the ME sensor. Simulation results indicate ECT based on ME sensors is especially applicable for non-ferromagnetic and low-conductivity materials, e.g. steel. One-dimensionally distributed cracks with varying crack sizes in a steel pipeline was then experimentally identified and located using ECT method. More importantly, the power consumption of our proposed ECT probe is as low as 0.625 uW, which shows 2–3 orders of magnitude improvement compared with other probes based on e.g. magnetoresistive (MR) sensors. Our research here provides a fundamental insight into NDT using ME sensors as a ECT probe and represents a crucial step towards online low-power monitoring of pipeline cracks.

Magneto-acoustic resonance in layered structure of ferrite and piezoelectric bimorph

The manuscript discusses a theoretical model that predicts a giant magnetoelectric (ME) coupling in laminates of ferrite and piezoelectric bimorph at the coincidence of electromechanical resonance for the electrical subsystem and ferromagnetic resonance for the ferrite. In such structures, the ME interaction is a result of mechanical strain. Using the piezoelectric bimorph gives rise to the excitation of high-order harmonic modes that are suppressed in ferrite-piezoelectric bilayers. ME coefficients, on the order of 590 V/A at 4.96 GHz, is predicted for the third resonance mode in laminate of yttrium-iron garnet and langatate bimorph. The phenomenon can be used for the realization of microwave sensors based on ME interaction.

Interfacial bonding effect on nonlinear magnetoelectric response of multiferroic composites

Magnetoelectric materials incorporate both ferroelectric and ferromagnetic phases to induce giant magnetoelectric coupling effect, which is one of the most important features and absent in either ferromagnetic or ferroelectric materials alone. ME effects is achieved through elastic deformation between the ferromagnetic and ferroelectric phases. It also depends on the constituent phase properties, the volume concentration and the interfacial conditions. In this paper, we investigate the interfacial effects on the nonlinear ME response of the multiferroic composites consisting both ferromagnetic and ferroelectric through epoxy bonding by using a unified micromechanics model. First, the nonlinear coupling behaviors of each individual ferromagnetic or ferroelectric phase are studied by consideration of evolution of the microstructure due to domain switching. Then, the coated or bonded inclusions are treated as a two-phase composite and a homogenization approach is applied to obtain the equivalent properties of the homogenized coated inclusions. Finally, the micromechanics approach is applied again to investigate the overall effective coupling properties of the multiferroic composites consisting coated inclusions and matrix. With a focus on the Terfenol-D/PZT/Terfenol-D system, we demonstrate how its coupling coefficients α33, and voltage coefficient αE33depend on the interfacial bonding. Comparisons between the theoretical calculations and the existing experimental data agree well.

Electric field control of magnetic susceptibility in laminate magnetostrictive/piezoelectric composites: Phase-field simulation and theoretical model

Electric field control of magnetic susceptibility in laminate magnetostrictive/piezoelectric composites promises to create a new class of magnetoelectric elements, voltage tunable inductors. To elucidate the underlying mechanism of electric field modulated magnetic susceptibility at the domain level, phase-field modeling, and computer simulation are employed to systematically study the laminate magnetoelectric composites of Terfenol-D and PZT, where polycrystalline Terfenol-D can provide a giant magnetoelectric coupling that is important for high-tunability voltage tunable inductors. The simulations focus on the interplay between magnetocrystalline anisotropy and stress-induced anisotropy that is induced by electric field and reveal three regimes of magnetic susceptibility behaviors: constant (regime I), fast-varying (regime II), and reciprocal linear (regime III), where regimes II and III can give rise to a high tunability. Such three regimes are attributed to different magnetization distribution and evolution mechanisms that are modulated by the stress-induced anisotropy. To further characterize the electric field control of magnetic susceptibility behaviors, a general theoretical model of laminate magnetoelectric (ME) composites based on polycrystalline magnetostrictive materials is developed, which reproduces the three regimes of susceptibility behaviors for polycrystalline Terfenol-D material. The general theoretical model for this specific system can also be extended to other laminate polycrystalline ME composites.

Field-induced magnetic incommensurability in multiferroicNi3TeO6

Using single crystal neutron scattering we show that the magnetic structure Ni$_3$TeO$_6$ at fields above 8.6 T along the $c$ axis changes from a commensurate collinear antiferromagnetic structure with spins along c and ordering vector $Q_C$= (0 0 1.5), to a conical spiral with propagation vector $Q_{IC}$= (0 0 1.5$\pm\delta$),$\delta\sim$0.18, having a significant spin component in the ($a$,$b$) plane. We determine the phase diagram of this material in magnetic fields up to 10.5 T along $c$ and show the phase transition between the low field and conical spiral phases is of first order by observing a discontinuous jump of the ordering vector. $Q_{IC}$ is found to drift both as function of magnetic field and temperature. Preliminary inelastic neutron scattering reveals that the spin wave gap in zero field has minima exactly at $Q_{IC}$ and a gap of about 1.1 meV consisting with a cross-over around 8.6 T. Our findings excludes the possibility of the inverse Dzyaloshinskii-Moriya interaction as a cause for the giant magneto-electric coupling earlier observed in this material and advocates for the symmetric exchangestriction as the origin of this effect.

Giant magnetoelectric coupling observed at high frequency in NiFe2O4-BaTiO3 particulate composite.

A giant magnetoelectric voltage coupling coefficient without direct current magnetic field observed in NiFe2O4–BaTiO3 particulate composite is reported. The particulate composite was obtained by combining hydrothermal and sol–gel method, and was studied for their crystallographic structure, morphology, magnetic, dielectric and magnetoelectric properties. Results of Mössbauer spectra demonstrated the presence of interface phase in particulate composite, where the changes of the magnetic properties in composite compared to the pure NiFe2O4 also confirmed this. The particulate composite exhibits remarkable magnetoelectric effect through both static measurement and dynamic measurement. The special magnetoelectric property of the particulate composite is beneficial for applications in high frequency devices.

Giant Magnetoelectric Coupling in Multiferroic PbTi1-x V x O3 from Density Functional Calculations.

Giant magnetoelectric coupling is a very rare phenomenon that has gained much attention in the past few decades due to fundamental interest as well as practical applications. Here, we have successfully achieved giant magnetoelectric coupling in PbTi1–xVxO3 (x = 0–1) using a series of generalized gradient-corrected GGA (generalized gradient approximation), including on-site Coulomb repulsion (U)-corrected spin-polarized calculations based on accurate density functional theory. Our total energy calculations show that PbTi1–xVxO3 stabilizes in C-type antiferromagnetic ground state for x > 0.123. With the substitution of V into PbTiO3, the tetragonal distortion is highly enhanced accompanied by a linear increase in polarization. In addition, our band structure analysis shows that for lower x values, the tendency to form two-dimensional magnetism of PbTi1–xVxO3 decreases. The orbital magnetic polarization was calculated with self-consistent field method by including orbital polarization correction in the calculation as well as from the computed X-ray magnetic dichroism spectra. A nonmagnetic metallic ground state is observed for the paraelectric phase for V concentration (x) = 1 competing with a volume change of 10% showing a large magnetovolume effect. Our orbital-projected density of states as well as orbital ordering analysis suggest that the orbital ordering plays a major role in the magnetic-to-nonmagnetic transition when going from ferroelectric to paraelectric phase. The calculated magnetic anisotropic energy shows that the direction [110] is the easy axis of magnetization for x = 1 composition. The partial polarization analysis shows that the Ti/V–O hybridization majorly contributes to the total electrical polarization. The present study adds a new series of compounds to the magnetoelectric family with rarely existing giant coupling between electric- and magnetic-order parameters. These results show that such kind of materials can be used for novel practical applications where one can change the magnetic properties drastically (magnetic to nonmagnetic, as shown here) with external electric field and vice versa.

Polarization-induced selective growth of single-crystal heterostructured multiferroic nanoplates with giant magnetoelectric coupling

Single-crystal heterostructured multiferroic (PbTiO3) PTO-(CoFe2O4) CFO nanoplate composites were prepared by a simple two-step hydrothermal process. The CFO nanoparticles with the size of 20–80 nm selectively grow on the positively polarized surface of the single-crystal and single-domain PTO nanoplate. The TEM results demonstrate an epitaxial growth relation between the PTO nanoplates and CFO nanoparticles. The results of the temperature-dependence magnetization of the composites under zero field cooled (ZFC) condition show a novel broad diffuse region around the PTO ferroelectric phase transition (Tc) for the first time. The total change of magnetization (Δ M) near Tc is determined to be (2.71 ± 0.5) × 10−3 emu, a change of 46.2%, implying a giant magnetoelectric coupling in these single-crystal heterostructured multiferroic PTO-CFO nanoplate composites. Such effect has been attributed to the absence of the substrate clamping and single domain in ferroelectric PTO nanoplate.

First-Principles Study of Magnetoelectric Coupling at Fe/BiFeO3(001) Interfaces

Multiferroics are important for controlling magnetization via electric field (rather than electric current), which is a main theme of spintronics research. However, single-phase multiferroic materials are not practical, due to their small magnetoelectric couplings. Here first-principles calculations predict giant magnetoelectric coupling at the interface between a single-phase multiferroic and a ferromagnet. The study provides microscopic physical insights into the control of magnetization by the electric field at a multiferroic interface, which should open a route to enhancing the efficiency of spintronic devices through low-power magnetic bit manipulation.

Magnetoelectricity in multiferroic hexaferrites as understood by crystal symmetry analyses

Magnetoelectric (ME) properties under rotating magnetic field H are comparatively investigated in two representative hexaferrites Y-type Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 and Z-type Ba0.52Sr2.48Co2Fe24O41, both of which have exhibited a similar transverse conical spin structure and giant ME coupling near room temperature. When the external H is rotated clockwise by 2pi, in-plane P vector is rotated clockwise by 2pi in the Y-type hexaferrite and counterclockwise by 4pi in the Z-type hexaferrite. A symmetry-based analysis reveals that the faster and opposite rotation of P vector in the Z-type hexaferrite is associated with the existence of a mirror plane perpendicular to c-axis. Moreover, such a peculiar crystal symmetry also results in contrasting microscopic origins for the spin-driven ferroelectricity; only the inverse DM interaction is responsible for the Y-type hexaferrite while additional p-d hybridization becomes more important in the Z-type hexaferrite. This work demonstrates the importance of the crystal symmetry in the determination of ME properties in the hexaferrites and provides a fundamental framework for understanding and applying the giant ME coupling in various ferrites with hexagonal crystal structure.

Vortex ferroelectric domains, large-loop weak ferromagnetic domains, and their decoupling in hexagonal (Lu, Sc)FeO3

The direct domain coupling of spontaneous ferroelectric polarization and net magnetic moment can result in giant magnetoelectric (ME) coupling, which is essential to achieve mutual control and practical applications of multiferroics. Recently, the possible bulk domain coupling, the mutual control of ferroelectricity (FE) and weak ferromagnetism (WFM) have been theoretically predicted in hexagonal LuFeO3. Here, we report the first successful growth of highly-cleavable Sc-stabilized hexagonal Lu0.6Sc0.4FeO3 (h-LSFO) single crystals, as well as the first visualization of their intrinsic cloverleaf pattern of vortex FE domains and large-loop WFM domains. The vortex FE domains are on the order of 0.1–1 μm in size. On the other hand, the loop WFM domains are ~100 μm in size, and there exists no interlocking of FE and WFM domain walls. These strongly manifest the decoupling between FE and WFM in h-LSFO. The domain decoupling can be explained as the consequence of the structure-mediated coupling between polarization and dominant in-plane antiferromagnetic spins according to the theoretical prediction, which reveals intriguing interplays between FE, WFM, and antiferromagnetic orders in h-LSFO. Our results also indicate that the magnetic topological charge tends to be identical to the structural topological charge. This could provide new insights into the induction of direct coupling between magnetism and ferroelectricity mediated by structural distortions, which will be useful for the future applications of multiferroics.

Voltage control of magnetism in NiZn ferrite/mica/PMNPT heterostructure with giant tunability and narrow linewidth

Recently, large magnetoelectric coupling of a spinel/piezoelectric heterostructure has been reported. However, the linewidth of the spinel is very large due to lattice mismatch when ferrite is directly deposited on piezoelectric substrates. This indicates a large magnetic loss, which impedes the spinel/piezoelectric heterostructure from useful device applications. Mica is a well-known 2D material, which can be split manually layer by layer without the substrate clamping effect. In this report, NiZn ferrite was deposited on a mica substrate by a spin-spray deposition technique. Spin-spray deposition is a wet chemical synthesis technique involving several chemical reactions for generating high-quality crystalline spinel ferrite films with various compositions directly from an aqueous solution. The thickness of ferrite is 2 μm, and the linewidth of the ferromagnetic resonance (FMR) is 115 Oe which is suitable for RF/microwave devices. The large FMR field tuning of 605 Oe was observed in NiZn ferrite/mica/PMN-PT heterostructures with minimal substrate clamping effect by reducing the thickness of the mica substrate. These multiferroic heterostructures exhibiting combined giant magnetoelectric coupling and narrow ferromagnetic resonance linewidth offer great opportunities for flexible RF magnetic devices.

Giant magneto-electric coupling in 100 nm thick Co capped by ZnO nanorods.

Here we report a giant, completely reversible magneto-electric coupling of 100 nm polycrystalline Co layer in contact with ZnO nanorods. When the sample is under an applied bias of ±2 V, the Co magnetic coercivity is reduced by a factor 5 from the un-poled case, with additionally a reduction of total magnetic moment in Co. Taking into account the chemical properties of ZnO nanorods measured by X-rays absorption near edge spectroscopy under bias, we conclude that these macroscopic effects on the magnetic response of the Co layer are due to the microstructure and the strong strain-driven magneto-electric coupling induced by the ZnO nanorods, whose nanostructuration maximizes the piezoelectric response under bias.

Voltage-Controlled On/Off Switching of Ferromagnetism in Manganite Supercapacitors.

The ever-growing technological demand for more advanced microelectronic and spintronic devices keeps catalyzing the idea of controlling magnetism with an electric field. Although voltage-driven on/off switching of magnetization is already established in some magnetoelectric (ME) systems, often the coupling between magnetic and electric order parameters lacks an adequate reversibility, energy efficiency, working temperature, or switching speed. Here, the ME performance of a manganite supercapacitor composed of a ferromagnetic, spin-polarized ultrathin film of La0.74 Sr0.26 MnO3 (LSMO) electrically charged with an ionic liquid electrolyte is investigated. Fully reversible, rapid, on/off switching of ferromagnetism in LSMO is demonstrated in combination with a shift in Curie temperature of up to 26 K and a giant ME coupling coefficient of ≈226 Oe V-1 . The application of voltages of only ≈2 V results in ultralow energy consumptions of about 90 µJ cm-2 . This work provides a step forward toward low-power, high-endurance electrical switching of magnetism for the development of high-performance ME spintronics.