Large Magnetoelectric Coupling Research Articles

Magnetic‐Field Controllable Displacement‐Type Ferroelectricity Driven by Off‐Center Fe2+ Ions in CaFe3Ti4O12 Perovskite

AbstractDisplacement‐type ferroelectrics usually exclude magnetic d‐electron contribution. Applying a magnetic field thus can little change the electric polarization. Herein, a magnetic ionic driven displacement‐type perovskite ferroelectric CaFe3Ti4O12 is reported. In this compound, magnetic Fe2+ ions contribute to both ferroelectric and antiferromagnetic orders respectively at TC ≈107 and TN ≈ 3.1 K, resulting in coupled electric and magnetic domains. A moderate magnetic field can induce a metamagnetic transition toward ferromagnetic correlations. External magnetic fields can thus readily tune the magnetic and the joint ferroelectric domains, giving rise to exceptional magnetic‐field controllable displacement‐type polarization with a large magnetoelectric (ME) coupling coefficient. This study opens up a new avenue to find unprecedented ME effects in displacement‐type ferroelectrics for numerous applications.

Magnetic Phase Transition-Induced Modulation of Ferroelectric Properties in Hexagonal RFeO3 (R = Tb and Ho).

Hexagonal rare-earth iron oxides (h-RFeO3) exhibit spontaneous magnetization and room-temperature ferroelectricity simultaneously. However, achieving a large magnetoelectric coupling necessitates further exploration. Herein, we report the impact of the magnetic phase transition on the ferroelectric properties of epitaxial h-RFeO3 (R = Tb and Ho) films prepared by pulsed laser deposition. The metastable h-RFeO3 phase is successfully stabilized with high crystallinity and low leakage current due to the ITO buffer layer, making it possible to investigate the ferroelectric properties. The h-TbFeO3 film exhibits a magnetic-field-induced transition from antiferromagnetic (AFM) to weak ferromagnetic (wFM) phases below 30 K, while also exhibiting ferroelectricity at 300 K. The dielectric constants change with the magnetic phase transition, demonstrating hysteresis in the magnetocapacitance. In contrast, the h-HoFeO3 film exhibits antiferroelectric-like behavior and an AFM-wFM phase transition. Notably, the h-HoFeO3 film shows a rapid increase in the remnant polarization during the AFM-wFM phase transition accompanied by an increase in the ferroelectric component. Considering the strong connection between the antiferroelectric behavior in the h-RFeO3 system and the ferroelectric domain wall motion, this considerable modification of ferroelectric properties during the magnetic phase transition is probably due to the faster movement of the ferroelectric domain walls in the wFM phase induced by the clamping effect. Our findings indicate the effectiveness of magnetic phase transitions in enhancing the magnetoelectric coupling, particularly when utilizing domain wall clamping properties.

Tunable self-biased magnetoelectric effect in magnetization-graded magnetoelectric composites

Magnetoelectric (ME) composites, which are magnetostrictive-piezoelectric composites, have garnered attention for use in various application fields owing to their large ME coupling compared with single-phase multiferroic materials. The maximum ME coupling is observed when an increased DC magnetic bias field is applied, which results in large devices with degraded sensitivity due to electromagnetic noise. To address this problem, a strong self-biased ME composite that generates the maximum ME response in a zero-bias field was proposed in this study. Highly self-biased ME composites were prepared by combining soft magnetic Ni and highly permeable Metglas magnetostrictive layers with a Pb(Mg1/3Nb2/3)O3–PbZrTiO3 piezoelectric single-crystal laminate structure and inducing a magnetization gradient. The maximum ME voltage value without a DC bias field was evaluated to be 4.2 V/cm∙Oe for an MMNPNMM (M: Metglas foil, N: nickel, P: PMN-PZT) structure, which is 625 % higher than that of conventional ME composites. Therefore, the relatively bulky means of the DC-bias application on ME materials could be eliminated, resulting in a simple ME device with a small volume using the magnetization gradient concept.

Can the ferroelectric soft mode trigger an antiferromagnetic phase transition?

Type-II multiferroics, where spin interactions induce a ferroelectric polarization, are interesting for new device functionalities due to large magnetoelectric coupling. We report on a new type of multiferroicity in the quadruple-perovskite BiMn3Cr4O12, where an antiferromagnetic phase is induced by the structural change at the ferroelectric phase transition. The displacive nature of the ferroelectric phase transition at 125 K, with a crossover to an order-disorder mechanism, is evidenced by a polar soft phonon in the THz range and a central mode. Dielectric and pyroelectric studies show that the ferroelectric critical temperature corresponds to the previously reported Néel temperature of the Cr3+ spins. An increase in ferroelectric polarization is observed below 48 K, coinciding with the Néel temperature of the Mn3+ spins. This increase in polarization is attributed to an enhanced magnetoelectric coupling, as no change in the crystal symmetry below 48 K is detected from infrared and Raman spectra.

Controlling magnetoelectric coupling effect of CoFe2O4–Ba0.8Sr0.2TiO3 multiferroic fluids by viscosity

The multiferroic fluids has an obvious magnetodielectric effects, and presents large magnetoelectric coupling coefficient of 89.8 V (cm Oe)−1.

Enhancement of magnetoelectric coupling and anisotropy by Galfenol/PZT/Galfenol magnetoelectric sandwich device

In this work, we reported the large magnetoelectric coupling coefficient and magnetoelectric coupling anisotropy in Galfenol/PZT/Galfenol 2-2 symmetric magnetoelectric sandwich devices. The directional solidification method was used to produce a Galfenol alloy with <001> orientation, which possesses a significant magnetostriction of 279 ppm and a piezomagnetic coefficient of 14.8 ppm/Oe. A magnetoelectric coupling laminate of Galfenol/PZT/Galfenol was also prepared. The magnetoelectric coupling coefficient can reach 55.0 V/cm Oe at the resonance frequency under a 0.35 Oe AC excitation magnetic field due to the significant magnetostriction and high piezomagnetic coefficient. Furthermore, there was excellent linearity and sensitivity between the magnetoelectric output voltage and the AC excitation magnetic field. Simultaneously, the device displayed in-plane magnetoelectric anisotropy and cosine variation as the magnetic field angle changed. At its resonance frequency, the device produced a maximum power of 1.4 mW. Finally, the device was shown to power 42 LEDs and a temperature/humidity sensor, demonstrating that the device withGalfenol/PZT/Galfenol sandwich structure has potential in magnetic field sensing and energy harvesting applications. • The device presented the in-plane anisotropy of ME coupling and cosine variation with the change of magnetic field angle. • The produced maximum power of the device was successfully demonstrated to power 42 LEDs and temperature/humidity sensors at its resonance frequency.

Magnetic and ionic liquid inclusions in soft materials and engineering enhanced electro-magneto-mechanical response

Magnetoelectric soft materials that polarize in the existence of external magnetic field and magnetize in response to an applied electric voltage have several promising technological applications. However, finding the suitable candidate for device fabrication has been a challenging task. Previous experiments and numerical modeling suggested an enhanced electrostrictive properties for soft materials composites made by depositing high permittivity liquid inclusions. Similarly, it has been reported that small magnetic inclusions significantly improve the magnetostrictive response of a soft composite. In this work, we highlight a simple yet effective mechanism to design soft materials composites with unusually large magnetoelectric coupling, merely by adding minute spherical liquid inclusions. Using a simple homogenization model, we explore the interplay of electrostatics, magnetostatics, soft solids and liquid inclusions on the effective coupling behavior of the soft composite while properly accounting for the capillary effects. This soft composite, which naturally allows large deformations, is also capable of generating electric voltage when subject to an external magnetic field. Meticulous selection of the size of liquid or solid inclusions, volume fraction and matrix materials properties significantly impacts the magnetoelectric coupling coefficient of the soft composite. In particular, choosing ferrofluids improves magnetoelectric response by 134% or higher. Moreover, in the absence of an electric field, a stronger magnetostrictive effect is revealed by ionic liquid inclusions compared to stiff ones, even in the presence of an applied mechanical strain.

Room-temperature multiferroicity in GaFeO3 thin film grown on (100)Si substrate

Room-temperature magnetoelectric multiferroicity has been observed in c-axis oriented GaFeO3 thin films (space group Pna21), grown on economic and technologically important (100)Si substrates by a pulsed laser deposition technique. Structural analysis and comprehensive mapping of the Ga:Fe ratio across a length scale range of 104 reveals coexistence of epitaxial and chemical strain. It induces formation of finer magnetic domains and large magnetoelectric coupling—a decrease in remanent polarization by ∼21% under ∼50 kOe. Magnetic force microscopy reveals the presence of both finer (&amp;lt;100 nm) and coarser (∼2 μm) magnetic domains. Strong multiferroicity in epitaxial GaFeO3 thin films, grown on a (100)Si substrate, brighten the prospect of their integration with Si-based electronics and could pave the way for development of economic and more efficient electromechanical, electrooptic, or magnetoelectric sensor devices.

Magnetoelectric, and dielectric based switching properties of co-doped BiFeO3 for low energy memory technology: A first-principles study

First-principles calculations are carried out to grow half-metallicity, tune dielectric and magnetoelectric properties of pure and doped bismuth ferrite BiFeO3 (BFO) with lanthanum (La) at A-site and cobalt (Co) at B-site as mono- and co-dopants. These calculations are performed in the Cambridge Serial Total Energy Package (CASTEP) code using ultra-soft pseudopotential (USP). A large band gap has been observed in the pure rhombohedral phase. The Co impurity atom is more favorable to decrease the band gap while La pushes the BFO towards half-metallic behavior, which develops 100% polarization in all doped BFO systems. From the dielectric response of BFO, high spin current density <s> of 8.7 × 103 A/m2 and charge current density (j) of 6.3 × 10–11 A/m2 have been observed in the La doped system. In the case of magnetic properties, the strong magnetization (M) 32.13 MA/cm2 and the large magnetoelectric coupling coefficient of 6.72× 10−6 s/m have been observed in co-doped BFO.

Modifying the Magnetic and Electronic Properties of Monolayer 2H‐VS 2 via Ferroelectric Substrate with Different Surface Terminations

A promising strategy to tailor the magnetic and electronic properties of 2D van der Waals magnets is to integrate them with a ferroelectric (FE) substrate. Herein, the FE substrate effect of BiFeO3(0001) with different surface terminations is explored using density functional theory calculations for the ferromagnetic 2H-VS2 monolayer. It is observed that depending on the polarization direction and surface termination of the BiFeO3(0001) FE substrate, the 2H-VS2/BiFeO3(0001) interface exhibits a substantially varied charge transfer behavior. The magnetic and electronic properties of the monolayer 2H-VS2 are significantly modulated by the interface charge transfer. Furthermore, in the 2H-VS2/BiFeO3(0001) heterostructures, large interface magnetoelectric coupling coefficients are predicted. The in-plane magnetic and electronic properties of monolayer 2H-VS2 can be effectively tuned by the out-of-plane FE polarization, paving the way for a novel class of spintronic devices based on the 2H-VS2/BiFeO3(0001) hybrid system.

Strong magnetoelectric coupling at an atomic nonmagnetic electromagnetic probe in bismuth ferrite

Isolated nonmagnetic substitutional defect ions experience huge coupled electric magnetic interaction in the single-phase multiferroic ${\mathrm{BiFeO}}_{3}$. In the ferroelectric state above the magnetic N\'eel temperature ${T}_{N}$, the electric environment generates a single symmetric electric field gradient (EFG) parallel to the electric polarization direction. Below ${T}_{N}$, a distinct magnetic interaction arises, monitored by the probe nuclei via their magnetic moment. Two magnetic environments arise, given by the relative angle of the local magnetic moment within its easy magnetic plane with respect to the EFG orientation. The angle between field gradient orientation and magnetic field direction is the most stable fitting parameter. The magnetic interaction concomitantly increases the EFG dramatically which reflects an outstandingly large local magnetoelectric coupling. In the set of best fits, two different electric environments form concurrently with two distinctly different local magnetic fields. The magnetic ordering in ${\mathrm{BiFeO}}_{3}$ thus completely distorts the electric environment of the nonmagnetic probe nucleus. The implications for the local effect of dopants in ${\mathrm{BiFeO}}_{3}$ are discussed. A third probe environment arising independent of temperature is identified and associated with an iron vacancy.

Observation of Anomalously Large Magnetoelectric Coupling in the Hexagonal Z‐Type Ferrite Films

AbstractAlthough the bulk hexaferrites are known to exhibit strong magnetoelectric (ME) effects near room temperature, the same effects are not realized in a thin film form. Herein, the growth of nearly epitaxial Co2Z‐type hexaferrite Ba0.3Sr2.7Co2Fe24O41 (BSCFO) thin films on a SrTiO3 (111) substrate by a chemical solution deposition method is reported. The reciprocal space mapping on the annealed BSCFO films reveals broadening along the qx directions in the (0014) and (0018) peaks, indicating that the oxygen planes belonging to the off‐centered octahedra have randomly distributed out‐of‐plane tilt to indicate significant disorder in the crystallographic orientation. Quantitative investigations reveal that both ME susceptibility and modulated electric polarization (ΔP) by magnetic field up to 370 K in the BSCFO films are always larger than those of the Co2Z‐type single crystal by ≈2–15 times and further increase upon having enhanced qx broadening in the (0014) and (0018) peaks. As the off‐centered octahedral sites can be a primary source of ΔP as predicted by the p–d hybridization mechanism, these results indicate that effective off‐centering could be further enhanced by the orientational disorder. This study identifies the potential of applying the ME hexaferrite films for multifunctional devices.

Observation of Spin‐Induced Ferroelectricity in a Layered van der Waals Antiferromagnet CuCrP2S6

AbstractCuCrP2S6, a van der Waals magnet having stacked layers of 2D honeycomb lattice made of CuS3 triangles and CrS6 octahedra, exhibits an A‐type antiferromagnetic order with the Néel temperature (TN) = 32 K. Upon in‐plane magnetic field (H) being applied below TN, H‐induced modulation of the c*‐axis electric polarization (ΔPc*) is found at fields lower than the saturation field µ0HS = 6.1 T, at which a forced ferromagnetic alignment sets in. Based on the symmetry analyses and dependence of ΔPc* on H and the azimuthal angle of applied H direction, a microscopic origin of the magnetoelectric (ME) coupling is attributed to the spin‐direction‐dependent p–d hybridization that is allowed due to the presence of off‐centered Cr3+ octahedra. A comparative study on CuCrP2Se6, however, finds no H‐induced P modulation due to cancellation of P between neighboring layers with the doubling of a crystallographic unit cell at TN. As the p–d hybridization mechanism allows generation of P in a single Cr atom–ligand pair, the results imply that large ME coupling should exist even in a single layer limit of CuCrP2S6.

The origin of the large magnetoelectric coupling in the ceramic Ba0.1Bi0.9(Ti0.9Zr0.1)0.1Fe0.9O3

57Fe Mössbauer spectrometry and x-ray powder diffraction are conducted to examine the structure and the local magnetic order at the level of Fe sites of Ba0.1Bi0.9(Ti0.9Zr0.1)0.1Fe0.9O3 ceramic. The Mössbauer spectra in the temperature range of 77 K–623 K were analyzed using a discrete distribution of hyperfine field, indicating that the Néel temperature T N was about 603 K. The ceramic Ba0.1Bi0.9(Ti0.9Zr0.1)0.1Fe0.9O3 remains stable in the rhombohedral structure (R3c) in the temperature range of 300 K–800 K. The anomaly of volume below T N, as detected from the model Debye–Gruneissen, reveals the presence of magnetoelastic coupling in this compound. The total polarization (P) obtained from Rietveld refined atomic positions is found to depend on the magnetic order that leads to the decrease of the total polarization (P) through the anomaly volume. The reduction in the polarization by ΔP ∼ −2.4 μC cm−2 suggests negative magnetoelectric interaction. The total polarization (P) obtained from Rietveld refined atomic is coupled with the magnetic ordering mediated by magnetoelastic coupling. The hyperfine field (B hf) dependence of polarization (P) at a temperature range below T N exhibits a linear evolution, confirming the linear magnetoelectric coupling. At room temperature, the linear magnetoelectric coefficient is about α ME ≈ 1.84 × 10−9 s m−1.

Tunable Magnetic Properties in SrRuO3/BiFeO3 Heterostructures via Electric Field

Tailoring the magnetism of multiferroic perovskite oxide heterostructures is vital for endowing spintronic devices with high density, small size, and low power consumption. In this work, the magnetism involving the magnetic moment and magnetic anisotropy of SrRuO3 (SRO)/BiFeO3 (BFO) heterostructures with different stacking patterns and electric field strengths is studied using first-principles calculations. It is found that the magnetic moments of part of the Ru atoms in SRO/BFO heterostructures can change from positive to negative with changes in the electric field strength. The inversion of the Ru magnetic moment induces a large magnetoelectric coupling strength of 1.31 × 10–10 G cm2/V. In addition, the SRO/BFO heterostructures show perpendicular magnetic anisotropy (PMA). The magnitude of PMA significantly changes with different stacking patterns and electric field strengths. These results suggest that the stacking pattern and the electric field strength are effective methods to modulate the magnetism in multiferroic perovskite oxide heterostructures, which is beneficial to promote the development of high-performance spintronic devices.

Magnetoelectric coupling in micropatterned BaTiO3/CoFe2O4 epitaxial thin film structures: Augmentation and site-dependency

The prominent magnetoelectric (ME) effect in ME composites usually originates from an interfacial strain-mediated coupling between ferroelectric and ferromagnetic components. While ME composite bilayer thin films have been proposed for microdevice applications, the ME coupling is usually diminished because of the substrate clamping effect. Here, we apply simple CMOS/MEMS compatible top-down fabrication techniques to ferroelectric BaTiO3 (BTO) and ferromagnetic CoFe2O4 (CFO) bilayer epitaxial thin films to control the substrate clamping. We found augmented ME coupling in micro-patterned bilayer thin films compared to the as-deposited films due to the reduced substrate clamping. In addition, a site-dependent ME coupling within the microstructure was observed. Larger ME coupling was obtained near the edge of the microstructure, and site-dependent ferroelectric imprints were observed on the micropattern. This can be attributed to the non-uniform substrate clamping across the film, and the strain gradient developed in the BTO layer due to the magnetostriction of CFO. Our findings provide additional insights to the design of micro- and nanoscale devices based on 2–2 ME composite thin films.

Multiferroic properties of the antiferroelectric-antiferromagnetic Cu9O2(SeO3)4Cl6

The recently experimentally observed multiferroic properties of the antiferroelectric-antiferromagnetic - Cu9O2(SeO3)4Cl6 are studied using a microscopic model and a Green's function technique. The sublattice polarization increases with decreasing temperature and increasing magnetic field h. For the total polarization which is zero without electric field E is observed a double hysteresis loop. The dielectric constant shows two anomalies at the two transition temperatures TN and TE. The magnetodielectric ratio increases with increasing magnetic field below TN. It is shown that a large magnetoelectric coupling g (E=0) or a strong external electric field E (g=const) induces a weak ferromagnetism in this compound. In analogy g (h=0) or an external magnetic field h (g=const) can lead to a weak ferroelectricity.

Yttrium iron garnet (YIG)/barium titanate (BTO) an engineered multiferroic nanocomposite

Novel lead-free multiferroic composites have recently attracted much attention due to large magneto-electric coupling achieved via mechanical strain. We fabricated multiferroic composites containing BaTiO3 (BTO) and Y3Fe5O12 (YIG) powders as (x = 0, 10, 30, 50 and 100 wt%). The phase formation, microstructure and magnetic properties were investigated successively. XRD confirms the Ia3̅d cubic symmetry of ferromagnetic YIG phase which is well dispersed in the tetragonal BTO ferroelectric matrix. The morphology revealed that the composites exhibit two well distributed phases. HRTEM images confirm that the nanocomposites have both YIG and BTO phase. The static and dynamic magnetic properties were studied using VSM and FMR. It is observed that saturation magnetization and anisotropy of nanocomposites increases with YIG wt% in BTO matrix and the Gilbert damping constant decreases with the increase of magnetization. The room temperature magneto-capacitance measurements revealed enhanced capacitance of about 20% at 120 Hz for an applied magnetic field of 14 kOe demonstrating improved magneto-electric coupling.

Antiferromagnetic-to-ferrimagnetic phase transition with large electric-polarization change in a frustrated polar magnet CaBaCo4O7

We investigate phase transitions of a geometrically frustrated polar magnet ${\mathrm{CaBaCo}}_{4}{\mathrm{O}}_{7}$, which exhibits the largest magnetoelectric (ME) effect in multiferroic compounds reported so far. Measurements of magnetization, sound velocity, and neutron diffraction of single crystals reveal an antiferromagnetic phase between the ferrimagnetic transition temperature ${T}_{\mathrm{C}}\ensuremath{\sim}60$ $\mathrm{K}$ and ${T}^{*}\ensuremath{\sim}69$ $\mathrm{K}$. In the antiferromagnetic phase, the ordered Co moments on the triangular layers remain nearly disordered. We demonstrate that a large electric-polarization change emerges upon the antiferromagnetic-to-ferrimagnetic transition. The large ME coupling can be attributed to the exchange striction.

Metamagnetoelectric transitions-enhanced multicaloric effect in multiferroics A2Cu2Mo3O12 (A=Rb and Cs) quantum spin chain

The multicaloric properties of multiferroic A 2 Cu 2 Mo 3 O 12 (A = Rb and Cs) compounds are theoretically investigated through a frustrated one-dimensional spin ribbon chain of CuO 2 . The system submitted to external magnetic and electric field constraints grants the particular interest of metamagnetoelectric effect arising at relatively low temperatures. The isentropes of Rb 2 Cu 2 Mo 3 O 12 and Cs 2 Cu 2 Mo 3 O 12 exhibit about four major sharper dips by lowering temperature. This highlights four meta-transitions points which in turn are simultaneously metamagnetic and metaelectric, and therefore conveniently treated as metamagnetoelectric transitions. In the vicinities of the metamagnetoelectric transitions and in the quantum critical region, the thermal entropies are relatively large, which thus results in metamagnetoelectric transitions-enhanced multicaloric effect. Furthermore, this enhancement appears in the cooling process where the adiabatic magnetic and electric cooling rates diverge in the vicinity of the metamagnetoelectric transition points indicating the prominent low-temperature multicaloric effect. It is then certain that by making use of such large magnetoelectric coupling at metamagnetoelectric transition regions, the refrigerating efficiency of multiferroic materials will be further improved. • The multicaloric properties of multiferroic A 2 Cu 2 Mo 3 O 12 (A = Rb and Cs) compounds are theoretically investigated. • The system submitted to external magnetic and electric field constraints exhibits the metamagnetoelectric effect. • The metamagnetoelectric transitions increase the thermal entropy, leading to an enhancement of the multicaloric effect. • The adiabatic cooling rates at the metamagnetoelectric transitions emphasize prominent low-temperature multicaloric effect.