Giant Magnetoelectric Research Articles

Strain-induced specific orbital control in a Heusler alloy-based interfacial multiferroics

For the development of spintronic devices, the control of magnetization by a low electric field is necessary. The microscopic origin of manipulating spins relies on the control of orbital magnetic moments (morb) by strain; this is essential for the high performance magnetoelectric (ME) effect. Herein, electric-field induced X-ray magnetic circular dichroism (XMCD) is used to determine the changes in morb by piezoelectric strain and clarify the relationship between the strain and morb in an interfacial multiferroics system with a significant ME effect; the system consists of the Heusler alloy Co2FeSi on a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Element-specific investigations of the orbital states by operando XMCD and the local environment via extended X-ray absorption fine structure (EXAFS) analysis show that the modulation of only the Fe sites in Co2FeSi primarily contributes to the giant ME effect. The density functional theory calculations corroborate this finding, and the growth of the high index (422) plane in Co2FeSi results in a giant ME effect. These findings elucidate the element-specific orbital control using reversible strain, called the ‘orbital elastic effect,’ and can provide guidelines for material designs with a giant ME effect.

High magnetoelectric coupling in piezoelectric modified BNT and magnetic NZFO particulate composite

Lead-free magnetoelectric (ME) particulate composite comprising piezoelectric 72.5Bi0·5Na0·5TiO3-22.5Bi0·5K0·5TiO3–5BiMg0·5Ti0·5O3 (MBNT) and piezomagnetic Ni0·7Zn0·3Fe2O4 (NZFO) in varying phase fraction, i.e., (1-x)MBNT-xNZFO (x = 0.05–0.30; Δx = 0.05) was prepared by solid state reaction route. Their structural, electrical, magnetic and ME properties were investigated. The high temperature sustainability up to 390 °C and the relaxor behavior was confirmed by their dielectric study. The room temperature dielectric constant (∼1081 at 1 kHz), saturation polarization (∼37.12 μC/cm2) and electro-strain (∼0.22 %) was observed maximum for pure MBNT, which decreases in composites with the induction of non-ferroelectric NZFO content. All composites exhibited magnetic hysteresis behavior where net increase in magnetization was associated with the relative increase in NZFO that possessed a saturation magnetization of 74.52 emu/g. At the optimum phase fraction of composite (i.e., 0.80MBNT-0.20NZFO), giant ME coefficient (∼58.12 mV/cm.Oe at 800 Oe) was observed at low frequency of 10 Hz, which suggest its credibility for energy harvester.

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.

A Low-Frequency MEMS Magnetoelectric Antenna Based on Mechanical Resonance.

Antenna miniaturization technology has been a challenging problem in the field of antenna design. The demand for antenna miniaturization is even stronger because of the larger size of the antenna in the low-frequency band. In this paper, we consider MEMS magnetoelectric antennas based on mechanical resonance, which sense the magnetic fields of electromagnetic waves through the magnetoelectric (ME) effect at their mechanical resonance frequencies, giving a voltage output. A 70 μm diameter cantilever disk with SiO2/Cr/Au/AlN/Cr/Au/FeGaB stacked layers is prepared on a 300 μm silicon wafer using the five-masks micromachining process. The MEMS magnetoelectric antenna showed a giant ME coefficient is 2.928 kV/cm/Oe in mechanical resonance at 224.1 kHz. In addition, we demonstrate the ability of this MEMS magnetoelectric antenna to receive low-frequency signals. This MEMS magnetoelectric antenna can provide new ideas for miniaturization of low-frequency wireless communication systems. Meanwhile, it has the potential to detect weak electromagnetic field signals.

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.

Collinear magnetic structure and multiferroicity in the polar magnet Co2Mo3O8

Among numerous multiferroic phenomena observed in spin frustrated lattice, giant magnetoelectricity in honeycomb lattice ${(\mathrm{Fe},\phantom{\rule{0.28em}{0ex}}\mathrm{Mn})}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ has stimulated great interest and substantial effort in searching for novel members in this 238 family. In this work, we synthesize successfully compound ${\mathrm{Co}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$, a structural analogue of ${\mathrm{Fe}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$, and present a series of characterizations on its structural, magnetic, and electric properties. An antiferromagnetic transition takes place at the Neel temperature ${T}_{N}=39\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ with appearance of electric polarization and dielectric anomaly, which provides clear evidence of simultaneous magnetic and ferroelectric transitions. The neutron powder diffraction (NPD) and magnetic susceptibility data confirm the $c$-axis collinear antiferromagnetic orders and emergent ferroelectric polarization. In particular, such antiferromagnetic order is relatively robust against magnetic field up to 9 T, different from ${\mathrm{Fe}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ with ferrimagnetic transition or ${\mathrm{Mn}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ with spin flop in the low-field region. Our data on single crystals demonstrate the second-order magnetoelectric effect in terms of magnetic field dependence of ferroelectric polarization response, while no linear magnetoelectric response is allowed. It is suggested that ${\mathrm{Co}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ provides a unique platform on which rich multiferroic physics in the presence of collinear magnetic order can be explored.

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.

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.

Thermal effects in magnetoelectric properties of NiFe2O4/Pb(Zr0.52Ti0.48)O3/NiFe2O4 tri-layered composite

ABSTRACTLayered composite electro-ceramics can be designed to exhibit the magnetoelectric (ME) effect based on stress transfer from magnetostriction of ferromagnetic layer to the ferroelectric layer. Many studies in search of giant ME coefficients in layered composites have been made but there are less studies regarding the ME effect in these ceramic materials as a function of temperature, mainly at low temperatures. With the influential increase in magnetoelectric sensing devices use in extreme, minute or precise field monitoring, a broadband temperature dependent analysis on ME effect of these sensors is much required. In this work the effect of temperature on ME effect in a NiFe2O4/Pb(Zr0.52Ti0.48)O3/NiFe2O4 layered composite are studied and any major/minute change have been analyzed. Dynamic ME measurements shows a maximum linear ME coefficient (αME = 238 mV/cm.Oe) by applying an AC magnetic field in a frequency of 600 Hz at room. Highly reduced αME values are observed at low temperatures. Magnetocapacitance effect studies showed a strong magnetoelectric coupling at room temperature and, also, a dramatic reduction in the magnetoelectric coupling at 200 K and 100 K. Analyzing the phenomena mathematically shows that there is a secondary effect interaction which influences the ME effect intensity depending on temperature.

Inverse bilayer magnetoelectric thin film sensor

Prior investigations on magnetoelectric (ME) thin film sensors using amorphous FeCoSiB as a magnetostrictive layer and AlN as a piezoelectric layer revealed a limit of detection (LOD) in the range of a few pT/Hz1/2 in the mechanical resonance. These sensors are comprised of a Si/SiO2/Pt/AlN/FeCoSiB layer stack, as dictated by the temperatures required for the deposition of the layers. A low temperature deposition route of very high quality AlN allows the reversal of the deposition sequence, thus allowing the amorphous FeCoSiB to be deposited on the very smooth Si substrate. As a consequence, the LOD could be enhanced by almost an order of magnitude reaching 400 fT/Hz1/2 at the mechanical resonance of the sensor. Giant ME coefficients (αME) as high as 5 kV/cm Oe were measured. Transmission electron microscopy investigations revealed highly c-axis oriented growth of the AlN starting from the Pt-AlN interface with local epitaxy.

Nonlinear resonant magnetoelectric coupling model for dual-peak phenomenon in magnetoelectric laminates

We investigated the dual-peak phenomenon in the response curve of the magnetoelectric (ME) coupling coefficient versus magnetic field for Terfenol-D/PZT/Terfenol-D tri-layer magnetoelectric laminated composites. Using nonlinear constitutive relations for the magnetostrictive material, an expression for the resonance ME coefficient that considers nonlinear resonance mechanical loss is established with the aid of the equivalent circuit method. The established model effectively predicts the complex behavior related to dual-peak phenomenon in regard to pre-stress, bias magnetic field, frequency of the alternating magnetic field, and nonlinear mechanical loss, and explains the origin of the dual peaks. The response curves obtained are consistent with experimental results. It can be found from the further predictions that in a given resonance frequency band, selecting an appropriate pre-stress can regulate two peaks in dual-peak curve, so that a giant ME coupling effect is obtained on the first peak, or a stronger resonance peak is achieved by adjusting stress to merge two peaks. With our resonance ME dual-peak model, we also demonstrate a giant ME coupling by regulating the dual-peak resonances by pre-stress engineering.

Giant magnetoelectric effect in negative magnetostrictive/piezoelectric/positive magnetostrictive semiring structure

Magnetoelectric (ME) Ni/PZT/TbFe2 and TbFe2/PZT composites with two semiring structures are prepared. The dependence between ME coupling and magnetostrictive property of the composite is discussed. Because Ni possesses negative magnetostrictive property and TbFe2 shows positive magnetostrictive property, the ME voltage coefficient of Ni/PZT/TbFe2 semiring structure is much larger than that of TbFe2/PZT. In these composites, the ME voltage coefficient increases and the resonance frequency gradually decreases with the increase of the semiring radius, showing that structural parameters are key factors to the composite properties. Due to the strong ME coupling effect, a giant ME voltage coefficient αE = 44.8 V cm−1 Oe−1 is obtained. This approach opens a way for the design of ME composites with giant ME voltage coefficient.

Magnetic origin of giant magnetoelectricity in doped Y-type hexaferrite Ba(0.5)Sr(1.5)Zn(2)(Fe(1-x)Al(x))(12)O(22).

We investigated site-specific magnetic behaviors of multiferroic Ba(0.5)Sr(1.5)Zn(2)(Fe(1-x)Al(x))(12)O(22) using Fe L(2,3)-edge x-ray magnetic circular dichroism. The Al dopants mostly replace the Fe(3+) ions at octahedral (O(h)) sites, which contribute unquenched angular momenta through off-centering displacements. This replacement greatly reduces the magnetic anisotropy energy to change the magnetic order from a helical to a heliconical type with enhanced magnetoelectric susceptibility (α(ME)). The tetrahedral (T(d)) Fe sites exhibit magnetic hysteresis distinguishable from that of the O(h) sites, especially at low magnetic fields. These results provide essential clues for the heliconical order with a giant α(ME) and multibit memory effects in the Al-doped Y-type hexaferrite.

Enhancing the magnetoelectric response of Terfenol-D/polyvinylidene fluoride/Terfenol-D laminates by exploiting the shear mode effect

Magnetoelectric (ME) composites have demonstrated high sensitivity for magnetic field sensor applications. Here, we report a ME laminate heterostructure consisting of magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy and piezoelectric polyvinylidene fluoride (PVDF) layers, both operated in shear mode. We show that the shear mode ME sensor exhibits a marked improved ME effect compared with the traditional ME composites operated in longitudinal and transverse piezoelectric and magnetostrictive modes using the same materials. A giant ME coefficient of 7.93 V/(cm·Oe) is obtained under a DC magnetic bias of 2300 Oe. The improved ME coefficient derives from the shear-mode heterostructure design, which allows both the Terfenol-D and PVDF to operate in shear mode that has maximum magnetoelectrical coupling coefficient.

Equivalent circuit method for resonant analysis of multilayer piezoelectric-magnetostrictive composite cantilever structures

In this paper, we discuss a theoretical model by the equivalent circuit method for magnetoelectric (ME) response at resonant frequencies corresponding to bending mode oscillations. A dynamic theoretical model of arbitrary multilayer cantilever with alternating piezoelectric (PE) and magnetostrictive (MS) layers on a substrate (Sub) was conducted. The equivalent circuit of the bending mode vibration has obtained by solving the piezoelectric, magnetostrictive and substrate constitutive equations under boundary conditions. The dependence of resonant frequencies and resonant ME coefficients on the material properties and structural dimensions is investigated. The ME coefficients were normalized by the total thickness of MS and PE layers and quality factor. As a demonstration, our theory for multilayer composite cantilever was then applied to specifically Metglas-AlN-Si systems. Our results demonstrate that the structural dimensions strongly influenced the neutral plane in the composite cantilever and then in turns strongly influenced the ME response. In addition, characteristics of multilayer ME cantilever in static (low frequency) station will be analyzed. The theory shows good agreement with experimental data. Our discussion may be helpful to the designing and fabrication of the giant ME cantilever with more realistic and optimal geometry.

The giant magnetoelectric effect in Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites

The Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites with excellent magnetoelectric (ME) coupling effect were synthesized by electrostatic spray depositing. The ME coupling characteristics of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites were investigated. It is found that the appropriate thickness ratio between magnetostrictive layers and piezoelectric layers (tm/tp) will be favorable to raise the resonance ME field output performance. The resonance frequency of ME field coefficient can be tuned by controlling tm/tp. The optimum resonance ME field coefficient of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites achieves 259.2 V/cm Oe at mechanical resonance frequency at 11.5 kHz with the dc bias magnetic field is 60 Oe. Remarkably, the proposed composites exhibit a giant ME effect and a higher ME voltage coefficient than the previous Terfenol-D/PZT laminated composites. It indicates that the mentioned Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites have great potential for the application of highly sensitive magnetic field sensing and vibration energy harvesting.

Investigation of optimized end-bonding magnetoelectric heterostructure for sensitive magnetic field sensor

This paper reports an optimized end-bonding magnetoelectric (ME) heterostructure FeCuNbSiB-PZT-FeCuNbSiB (FPF) for sensitive magnetic field sensor. The heterostructure is made by attaching magnetostrictive Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB) foils at the free ends of piezoelectric Pb(Zr1-x,Tix)O3 (PZT) plates. Due to the structural advantages, the FPF has ∼3.12 times larger resonance voltage coefficient (αME,r) than traditional FeCuNbSiB/PZT laminate. And compared with the Metglas-PZT-Metglas heterostructure, the FPF heterostructure has stronger ME responses for the excellent magnetic characteristics of FeCuNbSiB. In experiments, the FPF heterostructure is optimal designed through adjusting the thickness of PZT plate (tp) and the length of FeCuNbSiB foil (L). The results demonstrate that the maximum αME,r of 662.1 (V/cm Oe) is observed at 13 Oe DC bias magnetic field when L = 15 mm and tp = 0.6 mm. Based on the giant ME coupling, the DC magnetic field sensitivity for the optimized FPF heterostructure is 3.89 nT at resonant frequency. These results are very promising for the cheap room-temperature magnetic field sensing technology.

Enhanced Multipeak Magnetoelectric Effects in Ferromagnetic/Ferroelectric Composite With H-Shaped Elastic Substrate

A magnetoelectric (ME) composite consisting of FeCuNbSiB foils, Terfenol-D plates, piezoelectric PZT plates, and an H-shaped elastic substrate has been developed. The H-shaped elastic substrate severs as the multipeak frequency determining element. Due to the coupling between the H-shaped elastic substrate beams, an enhancement in the multipeak ME effect can be obtained compared with the conventional composite using a rectangle elastic substrate. The ME coefficient of the composite with two PZT plates electrically connected in series reaches 58.2 V/cm·Oe, which is ~4 times higher than that of the ME composite with the rectangle structure. The multipeak ME effects, along with the giant ME coupling, can be used in multifunctional devices, such as broadband energy harvesters or magnetic field sensors.

Enhanced magnetoelectric effect in ferromagnetic–elastic–piezoelectric composites

The non-magnetostrictive magnetoelectric (ME) effect was realized in a simple ferromagnetic–elastic–piezoelectric (FEP) composite. The FEP composite comprised two piezoceramic Pb(Zr,Ti)O3 (PZT) plates and NdFeB magnets elastically coupled by a cantilever beam made of phosphor copper-sheet. The effects of the beam length on the ME coefficient and the linear relationship between the ME voltage output and the applied magnetic field at the resonant frequency were experimentally investigated. A notably superior ME coefficient of 3800V/cmOe at extremely low resonant frequency of 5.524Hz was obtained for the FEP composite with the phosphor copper-sheet beam length of 8cm. Such a composite structure shows the possibility to obtain a magnetic sensor element with ultrahigh sensitivity in low frequency range. The results are of great importance for the basic understanding of the new way to realize giant ME effect and the optimal design of such a composite structure with high ME coefficient.