Large Magnetoelectric Response Research Articles

Mg doping enhanced magnetoelectric effect in the polar magnet Fe2Mo3O8

Magnetoelectric (ME) effect has given rise to a new design principle for novel low-power electronic devices. The polar magnet ${\mathrm{Fe}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ with linear ME effect is one of the promising candidates. Unfortunately, for this material, a large ME response only appears in the ferrimagnetic state, which needs a high magnetic field to be activated. In this work, we successfully synthesize single-crystal ${({\mathrm{Fe}}_{0.95}{\mathrm{Mg}}_{0.05})}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ (FMMO), which achieves a linear ME effect in the antiferromagnetic ground state and shows a significantly improved ME coefficient in the ferrimagnetic state. Compared with the parent phase, six times linear ME coefficient and more than ten orders of magnitude second-order ME coefficient are accomplished in the FMMO. The spin-lattice coupling and the exchange-striction mechanism are believed to play a crucial role in creating the giant ME effect. The present study provides an idea for designing materials with strong ME coupling.

Large magnetoelectric effect in BaFe12O19-(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 particulate composite

Multiferroic composites with a large magnetoelectric response are gaining attractive interests for the design of magnetoelectric (ME) functional devices. In this work, the particulate ME composites (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3–xBaFe12O19 (x=0, 0.1, 0.2, 0.3, 0.4 and 1) were prepared, and their structural, dielectric, magnetic, ferroelectric, piezoelectric properties and magnetoelectric coupling were systematically investigated. The composites consisted of only two chemically separated phases with well-bonded interface. Dielectric and impedance analyses indicated the co-contribution of grain and grain boundary to polarization. Well-saturated ferroelectric and magnetic hysteresis loops demonstrated multiferroic nature. ME response was investigated elaborately by employing magnetically induced polarization, together with measuring ME voltage coefficient and magnetodielectric value. Specifically, a large ME coefficient of 26.78 ​mV/cm·Oe was achieved for x=0.3, which is higher than that in single-phase BaFe12O19 and its coupled composites.

New Type of Anticommutative Dynamical Magnetoelectric Response.

Axion field induced topological magnetoelectric response has attracted lots of attention since it was first proposed by Qi etal. [Phys. Rev. B 78, 195424 (2008).PRBMDO1098-012110.1103/PhysRevB.78.195424]. Here we find a new type of anticommutative magnetoelectric response β^{ξ}(ω), which can induce a dynamical magnetoelectric current driven by a time-varying magnetic field. Unlike the Chern-Simons axion term, this magnetoelectric response term is gauge independent and nonquantized, and manifests in the systems breaking the symmetries of the time reversal, inversion, and mirror. In particular, we propose the antiferromagnetic material Mn_{2}Bi_{2}Te_{5} as a material candidate to observe dynamical magnetoelectric current, in which a large magnetoelectric response term β^{ξ}(ω) originates from band inversion.

Strain-Mediated Magneto-Electric Effects in Coaxial Nanofibers of Y/W-Type Hexagonal Ferrites and Ferroelectrics

Nanofibers of Y- or W-type hexagonal ferrites and core–shell fibers of hexagonal ferrites and ferroelectric lead zirconate titanate (PZT) or barium titanate (BTO) were synthesized by electrospinning. The fibers were found to be free of impurity phases, and the core–shell structure was confirmed by electron and scanning probe microscopy. The values of magnetization of pure hexagonal ferrite fibers compared well with bulk ferrite values. The coaxial fibers showed good ferroelectric polarization, with a maximum value of 0.85 μC/cm2 and 2.44 μC/cm2 for fibers with BTO core–Co2W shell and PZT core–Ni2Y shell structures, respectively. The magnetization, however, was much smaller than that for bulk hexaferrites. Magneto-electric (ME) coupling strength was characterized by measuring the ME voltage coefficient (MEVC) for magnetic field-assembled films of coaxial fibers. Among the fibers with Y-type, films with Zn2Y showed a higher MEVC than films with Ni2Y, and fibers with Co2W had a higher MEVC than that of those with Zn2W. The highest MEVC of 20.3 mV/cm Oe was measured for Co2W–PZT fibers. A very large ME response was measured in all of the films, even in the absence of an external magnetic bias field. The fibers studied here have the potential for use in magnetic sensors and high-frequency device applications.

Role of magnetic ordering in the phase coexistence at the structural instability of the multiferroic BiFeO3–PbTiO3

A promising approach for obtaining a large magnetoelectric response at room temperature in single-phase materials is to make use of phase-change phenomena at structural instabilities of a multiferroic state. This is the case of perovskites showing the morphotropic phase boundary (MPB) between ferroelectric polymorphs with differentiated magnetic orderings, like in BiFeO3–PbTiO3. Indeed, distinctive magnetoelectric effects were recently shown in Mn-modified BiFeO3–PbTiO3, associated with the electric field-induced phase transition between the coexisting MPB phases. We report here analogous effects under the magnetic field in 0.7BiFeO3–0.3PbTiO3, which shed light on the reversibility of the phase-change phenomena and the role of the magnetic ordering in the phase coexistence at the structural instability characteristic of the MPB. Results demonstrate magnetic field-driven phase-change phenomena.

Magnetoelectric effect in flexible nanocomposite films based on size-matching.

Flexible magnetoelectric (ME) nanocomposites with a strong coupling between ferromagnetism and ferroelectricity are of significant importance from the point of view of next-generation flexible electronic devices. However, a high loading of magnetic nanomaterials is needed to achieve preferable ME response due to the size mismatch of the magnetostrictive phase and piezoelectric phase. In this work, ultra-small CoFe2O4 nanoparticles were prepared to match the size of the polar crystal in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) is introduced to enhance the interplay between P(VDF-TrFE) and CoFe2O4. The above multiple effects promote a good connection between the magnetostrictive phase and the piezoelectric phase. Therefore, an effective transference of stress from CoFe2O4 to P(VDF-TrFE) can be achieved. The as-prepared P(VDF-TrFE)/CoFe2O4@POTS exhibits a high ME coupling coefficient of 34 mV cm-1 Oe-1 when the content of CoFe2O4@POTS is 20 wt%. The low loading of fillers ensures the flexibility of ME nanocomposite films.

Enhanced ferromagnetism and magnetoelectric response in quenched BiFeO3-based ceramics**Project supported by the National Natural Science Foundation of China (Grant Nos. 51672261 and 51373161) and the National Key Research and Development Program of China (Grant No. 2017YFA0701301).

The piezoelectric, ferromagnetism, and magnetoelectric response of BiFeO3–BaTiO3 ceramics with the compositions around the morphotropic phase boundary (MPB) of the solid solution are systematically investigated after the ceramics have been quenched from a high temperature. We find that the ferromagnetism of the quenched ceramics is greatly enhanced. An enhanced piezoelectric response d33 larger than 200 pC/N, which could be sustained up to 350 °C, is measured. As a result of enhanced ferromagnetism and piezoelectric response, a large magnetoelectric response ∼ 1.3 V/cm·Oe (1 Oe = 79.5775 A·m−1) is obtained near the mechanical resonance frequency of the quenched ceramic samples. Our research also shows that in addition to the ferromagnetism and piezoelectric response, the mechanical quality factor is another important parameter to achieve high magnetoelectric response because the physical effects are coupled through mechanical interaction in BiFeO3-based materials. Our work suggests that quenching is an effective approach to enhancing the magnetoelectric response of BiFeO3-based materials and the materials belong to single-phase multiferroic materials with high magnetoelectric response.

Improved room temperature magnetoelectric response in CoFe2O4-BaTiO3 core shell and bipolar magnetostrictive properties in CoFe2O4

A large Magnetoelectric (ME) response at room temperature in CoFe2O4 - BaTiO3 core shell composite is crucial for the biomedical application because of its biocompatibility. Good ME response of core–shell system is directly related to synthesis conditions as it determinesextent of coupling between core and shell structures. In this work, CoFe2O4 - BaTiO3 core shell structures with improved ME response were prepared through hydrothermal and citric gel synthesis. Reitveld refinement analysis and microscopic images confirmed the successful formation of CoFe2O4 - BaTiO3 core shell structure. The core shell sample is composed of tetragonal BaTiO3 and cubic spinel CoFe2O4 phases. CoFe2O4 was found to exhibit both positive and negative magnetostriction at room temperature. ME coefficient of 12.38 mV/cm Oe was observed at room temperature, which is quite high and can enhance the efficiency of targeted drug delivery.

Carrier-Density-Induced Ferromagnetism in EuTiO_{3} Bulk and Heterostructures.

EuTiO_{3} is an antiferromagnetic (AFM) material showing strong spin-lattice interactions, large magnetoelectric response, and quantum paraelectric behavior at low temperatures. Using electronic-structure calculations, we show that adding electrons to the conduction band leads to ferromagnetism. The transition from antiferromagnetism to ferromagnetism is predicted to occur at ∼0.08 electrons/Eu (∼1.4×10^{21} cm^{-3}). This effect is also predicted to occur in heterostructures such as LaAlO_{3}/EuTiO_{3}, where ferromagnetism is triggered by the formation of a high-density two-dimensional electron gas in the EuTiO_{3}. Our analysis indicates that the coupling between Ti 3d and Eu 5d plays a crucial role in lowering the Ti 3d conduction band in the ferromagnetic (FM) phase, leading to an almost linear dependence of the energy difference between the FM and AFM ordering on the carrier concentration. These findings open up possibilities in designing field-effect transistors using EuTiO_{3}-based heterointerfaces to probe fundamental interactions between highly localized spins and itinerant, polarized charge carriers.

Electric Field Control of Magnetism in Iron Oxide Nanoporous Thin Films

Voltage control of the magnetic properties of oxide thin films is highly appealing to enhance energy efficiency in miniaturized spintronic and magnetoelectric devices. Herein, magnetoelectric effects in electrolyte-gated nanoporous iron oxide films are investigated. Highly porous films were prepared by the evaporation-induced self-assembly of sol-gel precursors with a sacrificial block-copolymer template. For comparison, films with less porosity but analogous crystallographic structure were also prepared using an identical procedure except without the polymer template. The films were found to be 70-85 nm in thickness as measured by scanning electron microscopy and primarily hematite as determined by Raman spectroscopy. The templated (highly porous) films showed a very large magnetoelectric response with a maximum increase in magnetic moment at saturation of a factor of 13 and a noticeable (2-fold) increase of coercivity (after applying -50 V). The nontemplated films also exhibited a pronounced increase of magnetic moment at saturation of a factor of 4, although the coercivity remained unaffected over the same voltage range. Magnetoelectric effects in these latter films were found to be fully reversible in the voltage window ±10 V. The observed changes in magnetic properties are concluded to be magneto-ionically driven with oxygen ion exchange between the iron oxide and the liquid electrolyte, as evidenced from Raman and X-ray photoelectron spectroscopy experiments.

Large magnetoelectric response in lead free BaTi1−xSnxO3/NiFe2O4 bilayer laminated composites

Magnetoelectric studies on BaTi1−xSnxO3/NiFe2O4 (x = 0.07, 0.08, 0.09 and 0.10) lead-free bilayer laminated composites were investigated at 1 kHz and resonance frequencies. The pure phase formation of BaTi1−xSnxO3 and NiFe2O4 samples was confirmed by X-ray diffraction technique. The ferroelectric BaTi1−xSnxO3 layers of different compositions having large piezocoefficient were used for the ME studies. The composites displayed their maximum magnetoelectric voltage coefficient at resonance peaks related to the 1st radial mode. The thickness dependent magnetoelectric studies on composites with x = 0.08 revealed a giant magnetoelectric voltage coefficient of 24.53 V cm−1 Oe−1 at 285 kHz under bias field condition. Remarkably, a large self-biased magnetoelectric response of the order of ~ 2–5 V cm−1 Oe−1 at resonance was exhibited by the composites. The observed large and self-biased magnetoelectric response in BaTi1−xSnxO3/NiFe2O4 composites enables them to be a useful lead-free alternative for several magnetoelectric related applications.

Construction of Magnetoelectric Composites with a Large Room‐Temperature Magnetoelectric Response through Molecular–Ionic Ferroelectrics

Magnetoelectric materials with a large magnetoelectric response, a low operating magnetic (or electric) field, and a room-temperature (or higher) operating temperature are of key importance for practical applications. However, such materials are extremely rare because a large magnetoelectric response often requires strong coupling between spins and electric dipoles. Herein, an example of a magnetoelectric composite is prepared by using a room-temperature multiaxial molecular-ionic ferroelectric, tetramethylammonium tetrachlorogallate(III) (1). Investigation of the magnetoelectric effect of the magnetoelectric laminate composite indicates that its room-temperature magnetoelectric voltage coefficient (αME ) is as high as 186 mV cm-1 Oe-1 at HDC = 275 Oe and at the HAC frequency of ≈39 kHz, providing a valid approach for the preparation of magnetoelectric materials and adding a new member to the magnetoelectric material family.

Reversible and magnetically unassisted voltage-driven switching of magnetization in FeRh/PMN-PT

Reversible control of magnetization by electric fields without assistance from a subsidiary magnetic field or electric current could help reduce the power consumption in spintronic devices. When increasing temperature above room temperature, FeRh displays an uncommon antiferromagnetic to ferromagnetic phase transition linked to a unit cell volume expansion. Thus, using the strain exerted by an adjacent piezoelectric layer, the relative amount of antiferromagnetic and ferromagnetic regions can be tuned by an electric field applied to the piezoelectric material. Indeed, large variations in the saturation magnetization have been observed when straining FeRh films grown on suitable piezoelectric substrates. In view of its applications, the variations in the remanent magnetization rather than those of the saturation magnetization are the most relevant. Here, we show that in the absence of any bias external magnetic field, permanent and reversible magnetization changes as high as 34% can be induced by an electric field, which remain after this has been zeroed. Bulk and local magnetoelectric characterization reveals that the fundamental reason for the large magnetoelectric response observed at remanence is the expansion (rather than the nucleation) of ferromagnetic nanoregions.

Enhanced magnetoelectric coupling in Ti and Ce substituted lead free CFO-BCZT laminate composites

Lead-free multiferroic composites with enhanced magnetoelectric properties and sensitivity have potential for various multifunctional devices. The magnetoelectric behaviour of CoFe2O4-(Ba0.85Ca0.15) (Zr0.1Ti0.9)O3, (CFO-BCZT) and substituted CFO-BCZT laminate composites prepared by epoxy bonding are investigated in this study. Magnetostrictive CoFe2O4 (CFO) substituted with Ti (CTFO) resulted in a very high piezo-magnetic coefficient (q) of ∼290 × 10−9 Oe−1. Lead free piezoelectric (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 [BCZT] substituted with Ce4+ (BCZCT) showed improved piezoelectric coefficients of d33 ∼ 675 pC/N and g33 ∼13 mV m/N. Two new trilayer multiferroic laminates were developed with a (2-2) composite connectivity by combining the pure and substituted ferroic phases. Magnetostrictive, ferroelectric, piezoelectric and magnetoelectric properties of CFO-BCZT and CTFO-BCZCT laminate composites were measured and compared in here. CTFO-BCZCT composite exhibited a large magnetoelectric response with a high ME coefficient (αME) of ∼950 mV/cm.Oe and also showed an improved magnetoelectric sensitivity at lower magnetic fields, making it a potential lead-free material for magnetoelectric sensing applications.

Large magnetoelectric response and its origin in bulk Co-doped BiFeO3 synthesized by a stirred hydrothermal process

In this work, we study the effect of Co-doping on the magnetoelectric (ME) response of multiferroic BiFeO3 (BFO) ceramics made of powder synthesized using a stirred hydrothermal method known to facilitate chemical reactions and favor good chemical homogeneity and particles size distribution. An unprecedented ME coefficient up to 11.3 mV/(Oe.cm) i.e. 8 times higher than pure BFO ceramic, measured with a direct method is achieved for 3–5% Co-doping which makes bulk Co-doped-BFO among the largest single-phase ME materials. We show that Co-doping can be seen as a chemical pressure i.e. a proxy hydrostatic pressure resulting into an increase of Néel antiferromagnetic temperature and especially a destabilization of the cycloidal magnetic modulation because of magnetoelastic coupling. By suppressing the cycloidal arrangement that we evidenced unambiguously by using low energy Raman spectroscopy, the linear ME effect is no more inhibited and can then take place explaining the large ME response. We argue that the combination of mechanical and chemical means during the stirred hydrothermal approach we used might be at the origin of such response by favoring Co-distribution and avoiding parasitic phases and therefore such a chemical route might be further explored in the future.

Large resonance magnetoelectric response in Ni(Terfenol-d)/Pb(Zr,Ti)O3 bilayer laminate composites

In this work we report magnetoelectric laminate composites made up of negative magnetostrictive Ni plates, positive magnetostrictive Tb0.3Dy0.7Fe2 (Terfenol-d) plates and piezoelectric Pb(Zr,Ti)O3 (PZT) plates, in which negative and positive magnetostrictive plates are bonded on the piezoelectric plate and conjugate longitudinally with various orders. Both Ni-Terfenol-d-Ni/PZT and Terfenol-d-Ni-Terfenol-d/PZT composites are constructed and compared with Ni/PZT and Terfenol-d/PZT composites. The bias magnetic field and the frequency dependences of the magnetoelectric coefficient suggest that Ni-Terfenol-d-Ni/PZT is an optimal configuration with excellent magnetoelectric effects such as a large magnetoelectric coefficient at a low bias magnetic field and a low resonance frequency at which the maximum ME voltage coefficient appears. Besides, compared with most of other bulk composites configuration with Terfenol-d plates, the Ni-Terfenol-d-Ni/PZT composite reduces the Terfenol-d usage. We believe that the Ni-Terfenol-d-Ni/PZT composite is useful for the application due to its simple configuration and large resonance magnetoelectric response at a low frequency.

Giant room temperature magnetoelectric response in strain controlled nanocomposites

We report giant magnetoelectric coupling at room temperature in a self-assembled nanocomposite of BiFeO3-CoFe2O4 (BFO-CFO) grown on a BaTiO3 (BTO) crystal. The nanocomposite consisting of CFO nanopillars embedded in a BFO matrix exhibits weak perpendicular magnetic anisotropy due to a small out-of-plane compression (∼0.3%) of the magnetostrictive (CFO) phase, enabling magnetization rotation under moderate in-plane compression. Temperature dependent magnetization measurements demonstrate strong magnetoelastic coupling between the BaTiO3 substrate and the nanocomposite film, which has been exploited to produce a large magnetoelectric response in the sample. The reorientation of ferroelectric domains in the BTO crystal upon the application of an electric field (E) alters the strain state of the nanocomposite film, thus enabling control of its magnetic anisotropy. The strain mediated magnetoelectric coupling coefficient α=μodM/dE calculated from remnant magnetization at room temperature is 2.6 × 10−7 s m−1 and 1.5 × 10−7 s m−1 for the out-of-plane and in-plane orientations, respectively.

Controlling the Electrical and Magnetoelectric Properties of Epitaxially Strained Sr1−xBaxMnO3 Thin Films

The perovskite (Sr,Ba)MnO3 system is an ideal candidate for tailoring electrical and magnetoelectric properties through the accurate control of Ba content and epitaxial strain due to the strong coupling between polar instability, spin order, and lattice. Here, first, the polar order is proved to be induced in Sr1−xBaxMnO3 thin films through lattice expansion either by epitaxial strain or chemical pressure, which correlates with the evolution of the dielectric properties. Second, due to strong spin–phonon coupling, a large magnetoelectric response is found in the (Sr,Ba)MnO3 system, in which the dielectric constant drops up to 50% when the antiferromagnetic order emerges, larger than most magnetoelectric oxides. More important, this coupling between magnetism and dielectric properties can be tuned from ≈18% to ≈50% by appropriately selecting Ba content and epitaxial strain. Third, a clear trend of increasing the band gap energy on increasing the unit cell volume either by epitaxial strain or chemical pressure is found, which opens the way for engineering the semiconducting properties of (Sr,Ba)MnO3 system at will. Thus, this work proves the possibility to design the electrical response and the magnetoelectric coupling in (Sr,Ba)MnO3 system.

A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity.

There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3–BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3–BiMnO3–PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

Perovskite solid solutions with multiferroic morphotropic phase boundaries and property enhancement

Recently, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of phases in the BiFeO3–BiCoO3 perovskite binary system, associated with the existence of a discontinuous morphotropic phase boundary (MPB) between multiferroic polymorphs of rhombohedral and tetragonal symmetries. This might be a general property of multiferroic phase instabilities, and a novel promising approach for room temperature magnetoelectricity. We review here our current investigations on the identification and study of additional material systems, alternative to BiFeO3–BiCoO3 that has only been obtained by high pressure synthesis. Three systems, whose phase diagrams were, in principle, liable to show multiferroic MPBs have been addressed: the BiMnO3–PbTiO3 and BiFeO3–PbTiO3 binary systems, and the BiFeO3–BiMnO3–PbTiO3 ternary one. A comprehensive study of multiferroism across different solid solutions was carried out based on electrical and magnetic characterizations, complemented with mechanical and electromechanical measurements. An in-depth structural analysis was also accomplished when necessary.