Weak Magnetoelectric Coupling Research Articles

Exotic role of poling protocol on augmentation of magnetoelectricity in BCZT/CNZF layered composites

Here, we report exotic role of electrical poling of layered BCZT-CNZF bulk composite for a sustainable advancement of magnetoelectric (ME) technology. Practically, it seems quite difficult to access full potential of ME composites due to their weak ME coupling performances. Using a standard poling protocols, we successfully deployed coupling performance of laminated ME composite, comprises of ferroelectric (FE) layer of BCZT and a ferrite layer of CNZF. However, the ME coupling constant of laminated composite is optimized by lowering volume fraction of FE component to strengthen the mechanical strain in piezoelectric layer, while fixing the thickness of the magnetostrictive ferrite layer. Here, we employed systematic zero field cooled (ZFC) and field cooled (FC) electrical poling protocol on morphotropic phase boundary (MPB) based BCZT composition, well-appreciated for it’s remarkable electromechanical activity. We report a record augmentation in magnetoelectric coupling as a consequence of prudent field cooled poling mechanism. On the basis of our findings, we emphasize that the degree of magnetoelectricity may be significantly improved for miniaturization of efficient devices via proper execution of poling technique.

Spin dynamics, critical scattering and magnetoelectric coupling mechanism of Mn4Nb2O9

The spin dynamics of Mn4Nb2O9 were studied using inelastic neutron scattering. A dynamic model is proposed to explain the observed spin-wave excitation spectrum from Mn4Nb2O9. The model indicates that the exchange interactions along the chain direction are weakly ferromagnetic while the exchange interactions between the neighbour chains are strongly antiferromagnetic. The antiferromagnetic interactions on the two MnO6 octahedron networks are dominant in the spin dynamics of this compound. A spin gap of about 1.4 meV was observed at the zone centre, which is attributed to the weak easy-axis magnetic anisotropy of Mn2+ ions. Magnetic critical scattering from Mn4Nb2O9 was studied in the vicinity of its Néel temperature T N as well, indicating homogeneous development of magnetic correlations. According to the symmetry analysis and its magnetic structure, the weak magnetoelectric coupling effect in Mn4Nb2O9 is ascribed to the uncancelled exchange striction on the two non-equivalent Mn2+ sites.

Lattice symmetry breaking transition and critical size limit for ferroic orders in nanophase BiFeO3

Finite size effects on the ferroic orders in $\mathrm{BiFe}{\mathrm{O}}_{3}$ are studied by atomic pair distribution function analysis and magnetic measurements. While bulk rhombohedral $\mathrm{BiFe}{\mathrm{O}}_{3}$ exhibits ferroelectricity and antiferromagnetism with a cycloidal magnetic moment arrangement leading to zero magnetization and weak magnetoelectric coupling, $\mathrm{BiFe}{\mathrm{O}}_{3}$ nanoparticles with a size smaller than the spin cycloid period of 62 nm preserve their polar rhombohedral structure and develop ferromagnetism, thus exhibiting coexisting polarization and nonzero magnetization that enhances the magnetoelectric coupling. When the nanoparticles become smaller than 17 nm, however, their crystal lattice expands and becomes nonpolar cubic. They also become superparamagnetic and thus simultaneously cease exhibiting both ferroelectricity and ferromagnetism. Our findings shed light on the interaction between the lattice structure and ferroic orders in nanophase perovskites and also provide a rare example of a lattice symmetry breaking phase transition that determines their critical size.

Electric-field-controlled magnetism due to field-induced transition of Pna21/R3c in Bi1-xGdxFeO3 ceramics

BiFeO3 has been recognized as one of the most important room-temperature single-phase multiferroic materials, but it still suffers from several drawbacks especially the weak magnetoelectric coupling. In the present work, the electric-field-controlled magnetism is achieved in Bi1-xGdxFeO3 system, which involves a field-induced transition of Pna21/R3c at the morphotropic phase boundary region, and the magnetic state is switched between cycloidal state and canted antiferromagnetic state. The electric-field-controlled magnetism becomes reversible with the help of annealing, which is confirmed by magnetic hysteresis loops and the quantitative ratio of the involved phases for the as-sintered, as-poled and as-annealed samples. Compared with the systems of Bi1-xNdxFeO3 and Bi1-xSmxFeO3, it is easier to tune the symmetry from R3c to Pna21 with lower rare earth-content, and the field-induced transition is more apparent and subsequently leads to more significant electric-field-controlled magnetism in a wider composition range.

Pressure and magnetic field effects on ferroelastic and antiferromagnetic orderings in honeycomb-lattice Mn2V2O7

The multiferroic nature of the honeycomb-lattice $\mathrm{M}{\mathrm{n}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ was investigated through detailed temperature, high-pressure, and magnetic-field-dependent measurements. A first-order martensiticlike structural phase transition with the thermal hysteresis associated with magnetic, heat-capacity, and dielectric anomalies was observed between ${T}_{Mh}$ (303 K) and ${T}_{Mc}$ (291 K). External pressure up to 15.41 kbar suppresses the thermal hysteresis in the magnetization data, indicating that the high-temperature \ensuremath{\beta}-phase persists down to the lower temperature under 15.41 kbar. Furthermore, isothermal capacitance-stress hysteresis loops along with crystallographic Aizu notation of $2/mF\overline{1}$ supports a martensitic phase transition driving ferroelastic ordering near or below room temperature. At low temperature, a long-range antiferromagnetic ordering was observed at ${T}_{N}\ensuremath{\sim}17\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. With increasing the external pressure up to 15.41 kbar, 100% enhancement of ${T}_{N}$ was observed and a metamagnetic transition at 5 K was enhanced near 3 T. High-field magnetization study up to 60 T induces multiple metamagnetic transitions below ${T}_{N}$. Below ${T}_{N}$, a magnetostriction induced magnetoelectric coupling was observed and further supported by the temperature-dependent x-ray studies. Taking these comprehensive research findings into account, we established that $\mathrm{M}{\mathrm{n}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ is a unique multifunctional material with the coexistence of ferroelastic and antiferromagnetic orderings and with weak magnetoelectric coupling.

Constructing Asymmetrical Ni-Centered {NiN2O4} Octahedra in Layered Metal-Organic Structures for Near-Room-Temperature Single-Phase Magnetoelectricity.

Layered metal-organic structures (LMOSs) as magnetoelectric (ME) multiferroics have been of great importance for realizing new functional devices in nanoelectronics. Until now, however, achieving such room-temperature and single-phase ME multiferroics in LMOSs have proven challenging due to low transition temperature, poor spontaneous polarization, and weak ME coupling effect. Here, we demonstrate the construction of a LMOS in which four Ni-centered {NiN2O4} octahedra form in layer with asymmetric distortions using the coordination bonds between diphenylalanine molecules and transition metal Ni(II). Near room-temperature (283 K) ferroelectricity and ferromagnetism are observed to be both spontaneous and hysteretic. Particularly, the multiferroic LMOS exhibits strong magnetic-field-dependent ME polarization with low-magnetic-field control. The change in ME polarization with increasing applied magnetic field μ0H from 0 to 2 T decreases linearly from 0.041 to 0.011 μC/cm2 at the strongest ME coupling temperature of 251 K. The magnetic domains can be manipulated directly by applied electric field at 283 K. The asymmetrical distortion of Ni-centered octahedron in layer spurs electric polarization and ME effect and reduces spin frustration in the octahedral geometry due to spin-charge-orbital coupling. Our results represent an important step toward the production of room-temperature single-phase organic ME multiferroics.

Ferroelectrically tunable magnetism in BiFeO3/BaTiO3 heterostructure revealed by the first-principles calculations

The perovskite oxide interface has attracted extensive attention as a platform for achieving strong coupling between ferroelectricity and magnetism. In this work, robust control of magnetoelectric (ME) coupling in the BiFeO3/BaTiO3 (BFO/BTO) heterostructure (HS) was revealed by using the first-principles calculation. Switching of the ferroelectric polarization of BTO induce large ME effect with significant changes on the magnetic ordering and easy magnetization axis, making up for the weak ME coupling effect of single-phase multiferroic BFO. In addition, the Dzyaloshinskii-Moriya interaction (DMI) and the exchange coupling constants J for the BFO part of the HSs are simultaneously manipulated by the ferroelectric polarization, especially the DMI at the interface is significantly enhanced, which is three or four times larger than that of the individual BFO bulk. This work paves the way for designing new nanomagnetic devices based on the substantial interfacial ME effect.

Magneto dielectric coupling in Bi2Fe4O9

This work reports multiferroic behaviour of bulk Bi2Fe4O9 exhibiting both weak ferromagnetic and ferroelectric behaviour at room temperature. Importantly the ferroelectric parameters and dielectric constant are observed to be sensitively dependent upon the magnetic field indicating the occurrence of spin charge coupling. Based on the dielectric measurements under the application of magnetic field, the magneto dielectric coupling (MD %) is found to vary from 0% to about −20% with increasing magnetic field. The observed variation in MD% is attributed to the weak magnetoelectric coupling in such systems.

Reversible modulation of magnetic anisotropy and coercivity triggered by external bias voltage in CoFe2O4/Pb(Mg1/3Nb2/3)O3–PbTiO3 multiferroic heterostructures

Multiferroic materials have been studied extensively in recent years as their abundant fundamental physics and technological applications. As we known, although multi order of ferroics can exist in one compound, these materials usually exhibit weak magnetoelectric coupling and low Curie temperature. Therefore multiferroic heterostructure is employed as a solution for the enhanced magnetoelectric response and its wide temperature survival. In this study, the magnetic property of, especially under electric field, multiferroic heterostructure CoFe2O4/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (CFO/PMN-PT) has been comprehensively explored. By the magneto-optical Kerr effect measurement, it is found that the magnetic properties of CoFe2O4 (CFO) thin film is tunable and reversible by the external electric field as the piezoelectric nature of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT). The in-plane magnetic anisotropy of CFO film is observed distinctly, and the difference value of the coercive field with magnetic field along PMN-PT [0 0 1] and [1 1¯ 0] changes from 608 to 841 Oe by the electric field. The strain dependence of the change of coercive field has been demonstrated by both experimental and theoretical study, revealing the coupling mechanism in the heterostructure. Our result shows that the multiferroic heterostructure CFO/PMN-PT exhibits the application of electric field controlled exchange bias and the electric field assisted data storage device.

Magnetocrystalline anisotropy in the Co/Fe codoped Aurivillius oxide with different perovskite layer number

AbstractPerpendicular magnetic anisotropic materials are of great interest for their huge potential to realize high‐density nonvolatile memory and logic chips. Designing such materials with lower cost and better magnetoelectric coupling still remains major challenges. In this work, aurivillius oxide ceramics with highly [00l]‐oriented grains were prepared by a facile pressureless sintering method, and the perovskite layer number was modified by varying the cobalt content. Afterwards, the unique perpendicular magnetic anisotropy and the intriguing anisotropic ferroelectric properties have been observed. The magnetic properties of the Aurivillius oxides with different layer numbers have been carefully investigated by field cooling, zero field cooling, and the magnetization with a varying field. The magnetic anisotropy in the oriented ceramics is demonstrated to be caused by the magnetocrystalline anisotropy with the easy magnetization direction along the c‐axis, which possibly arises from the unquenched 3d orbitals combined with the special layered crystal structures. The magnetocrystalline anisotropy becomes weaker in the ceramics with lower numbered perovskite layers, whereas the orientation degree of the ceramics and the ferroelectric anisotropy show quite opposite trends. Furthermore, the weak magnetoelectric coupling is also observed in the ceramics. This special anisotropic multiferroic properties may open up a new window for the Aurivillius materials.

Temperature dependence of electric field tunable ferromagnetic resonance lineshape in multiferroic heterostructure

Herein, we experimentally investigate the effect of temperature on the electric field tunable ferromagnetic resonance (FMR) in a ferroelectric/ferromagnetic heterostructure, and demonstrate the tuning of abnormal change in FMR using the polarization of the ferroelectric layer above 200 K. The FMR was found to be almost unchanged under different electric field strength at 100 K owing to frozen polarization, which causes extremely weak magnetoelectric coupling. More interestingly, negative effective linewidth was observed when an electric field greater than 10 kV/cm was applied above 220 K. The simultaneous electrical control of magnetization and its damping via FMR based on linear magnetoelectric coupling are directly relevant to use of composite multiferroics for a wide range of devices.

Electric and Magnetic Properties of ALD-Grown BiFeO3 Films

The magnetization and electric polarization in thin bismuth ferrite films (BFO) films have been under extensive study for high technological potential of single-phase multiferroic materials. Surpassing the antiferromagnetic nature and weak magneto-electric coupling of bulk BFO has required highly specialized substrates and epitaxial growth methods so far. Polycrystalline single-phase multiferroic BFO (50–500 nm thick) films were grown by atomic layer deposition (ALD) on technologically simple Pt/SiO2/Si substrates. The BFO films were found to exhibit strong saturating ferromagnetism and coercivity at temperatures ranging from cryogenic to room temperature even with 500 nm thick layers, a property which cannot be obtained with thick epitaxial films or bulk BFO. The magnetization mechanism was associated with magnetic domain wall dynamics and collapsing of the helimagnetic spin modulation. The electric properties were found to be strongly dependent on the film thickness. The film crystallization, compositio...

Magnetoelectric coupling characteristics in multiferroic heterostructures with different thickness of nanocrystalline soft magnetic alloy

Magnetoelectric(ME) coupling characteristics in multiferroic heterostructures with different thickness of nanocrystalline soft magnetic alloy has been investigated at low frequency. The ME response with obvious hysteresis, self-biased and dual-peak phenomenon is observed for multiferroic heterostructures, which results from strong magnetic interactions between two ferromagnetic materials with different magnetic properties, magnetostrictions and optimum bias magnetic fields Hdc,opti. The proposed multiferroic heterostructures not only enhance ME coupling significantly, but also broaden dc magnetic bias operating range and overcomes the limitations of narrow bias range. By optimizing the thickness of nanocrystalline soft magnetic alloy Tf, a significantly zero-biased ME voltage coefficient(MEVC) of 14.8mV/Oe (185 mV/cm⋅ Oe) at Tf = 0.09 mm can be obtained, which is about 10.8 times as large as that of traditional PZT/Terfenol-D composite with a weak ME coupling at zero bias Hdc,zero. Furthermore, when Tf increases from 0.03 mm to 0.18 mm, the maximum MEVC increases nearly linearly with the increased Tf at Hdc,opti. Additionally, the experimental results demonstrate the ME response for multiferroic heterostructures spreads over a wide magnetic dc bias operating range. The excellent ME performance provides a promising and practicable application for both highly sensitive magnetic field sensors without bias and ME energy harvesters.

Direct observation of magnetodielectric effect in type-I multiferroic PbFe0.5Ti0.25W0.25O3

In type-I multiferroics, where ferroelectricity and magnetism arise from different origins, the explicit measurement of magnetoelectric effect is commonly prohibited due to the weak magnetoelectric coupling. From our investigation of magnetic and dielectric properties in a perovskite PbFe0.5Ti0.25W0.25O3, we have directly demonstrated magnetic-field-driven change of dielectric constant in a highly non-linear fashion. Our result offers a potential utilization of magnetoelectric functionality in type-I multiferroics.

Magnetoelectric coupling across the interface of multiferroic nanocomposites

In recent decades, magnetoelectric effect in multiferroic materials has attracted extensive attention owing to the upcoming demands for new-generation multi-functional magnetoelectronic devices, such as transducer, sensor and so on. This gives people a strong push to explore the multiferroic materials with a reduced dimension and effective coupling between electric and magnetic orderings, especially at room temperature. Due to the weak magnetoelectric coupling strength in sing-phase multiferroic materials, scientists start to design nanocomposites and artificial nanostructures with strong coupling among order parameters (lattice, charge, spin and orbital). In this review, we will introduce recent major progresses of magnetoelectric coupling in multiferroic nanocomposites across their interfaces from the following four aspects: strain effect, charge transfer, magnetic exchange interaction and orbital hybridization, based on their coupling mechanisms. Through a full understanding of the above coupling among these orderings, it is possible to achieve the nanoscale modulation of magnetization (ferroelectric polarization) by external electric (magnetic) field. Apart from the magnetoelectric coupling, those artificially functional nanocomposites provide us a platform to explore and study the emerging physical phenomena so that we can design self-assembled nanostructures to tailor novel functionalities in future applications.

Using Raman and dielectric spectroscopy to elucidate the spin phonon and magnetoelectric coupling in DyCrO3 nanoplatelets

In this study, we report the phonon-mode assignment and possible weak magnetoelectric coupling by Raman & dielectric spectroscopy along with efficient photocatalytic activity of DyCrO3 nanoplatelets.

Multiferroic / Magneto-Electric Composite Thin Films: A Review of Recent Patents

Composites (3-0 and 2-0) and multilayers (2-2 geometry) of magnetoelectric multiferroics have recently attracted immense research interest owing to their potential applications like memory/storage devices, FETs, energy harvesters, sensors and transducers. Thin film based multiferroics and magnetoelectrics have special significance because of their direct integration into the device fabrication industry. Hence, a fundamental research in this area along with the fabrication of versatile devices needs a thorough investigation. This review article mainly focuses on the developments of device level works in this particular area in which the discussion of recent patents is highlighted. Generally, thin film magneto electrics and multiferroics show weak magneto electric coupling properties compared to their bulk cousins due to their high substrate clamping. However, some of the recent research developments in thin film based magneto electrics and multiferroics show promising future. In this article, a general patent search in thin films is provided along with a special thrust given to the nanocomposite based multiferroics and magneto electric films. Keywords: Magnetism, magnetoelectrics, multiferroics, piezoelectrics, spintronics, storage medium.

Giant self-biased magnetoelectric response with obvious hysteresis in layered homogeneous composites of negative magnetostrictive material Samfenol and piezoelectric ceramics

Giant self-biased magnetoelectric (ME) response and obvious hysteresis are observed in trilayer homogenous ME laminate composite consisting of negative magnetostrictive Samfenol (SmFe2) plates and piezoelectric ceramic PZT (Pb(Zr,Ti)O3) plates. The large anisotropic field of SmFe2 oriented the direction [111] of easy magnetization results in an enhanced internal bias due to its huge intrinsic anisotropic constant. The experimental results demonstrate that this composite exhibits ∼30 times higher ME voltage coefficient than that of composite FeNi/PZT/FeNi with weak ME coupling at zero bias. These results provide the possibility of this homogeneous ME composite for ultra-sensitive magnetic field sensing without bias.

Stepwise technique for accurate and unique retrieval of electromagnetic properties of bianisotropic metamaterials

Metamaterials (MMs) are artificial materials that have received attention recently because their built-in features create collective electromagnetic effects that are otherwise impossible, such as negative refraction, and because of their exotic electromagnetic applications, namely, perfect lens and invisibility cloaks. Depending on wave propagation characteristics, MMs possessing normally weak magneto-electric coupling coefficients start to exhibit stronger bianisotropic effects. Therefore, accurate electromagnetic characterization of these MMs is important. In this study, we adapt a stepwise method based on the Nicolson–Ross–Weir technique for accurate and unique retrieval of electromagnetic properties of bianisotropic MM slabs. For this goal, we have derived explicit expressions for unique retrieval of electromagnetic properties of these slabs and compared these expressions with those in the literature in the retrieval process. From the comparison, we note that derived expressions are appropriate for unique determination of electromagnetic properties of bianisotropic MM slabs. In the performance analysis of the stepwise method for different measurement scenarios, we considered different bianisotropic MM cell configurations (split-ring and Omega-shaped resonators as well as the same resonators with wire strips) and extracted their electromagnetic properties when measured/simulated scattering parameters have some thermal noise. We note that for most of the frequencies, the stepwise method retrieves correct electromagnetic properties even when a relatively higher normally distributed noise with zero mean value and with standard deviations of 0.015 is present. In addition to the influence of thermal noise on performance of the stepwise method, we also analyzed the effect of both increasing length slab and the frequency band on retrieved electromagnetic properties of the analyzed various bianisotropic MM slabs.

Multifunctional hybrid structures of ferromagnetic FePt and ferroelectric BaTiO3nanoparticles: facile synthesis and characterization

Nanohybrid structures of FePt and BaTiO3 with bifunctional properties were synthesized by a two step synthesis procedure including solid state and solvothermal methods. Two different compositions of FePt and BaTiO3 nanoparticle samples were synthesized. The hybrid composite, having the lower FePt concentration, exhibited bifunctionality including superparamagnetism with a blocking temperature near room temperature and ferroelectricity at ambient conditions. Magnetocapacitive measurements of this bifunctional FePt–BiTiO3 sample showed behaviour typical of weak magnetoelectric coupling. This synthetic approach provides a general method for preparing advanced multifunctional and technologically important ceramic–alloy hybrids.