Magnetoelectric effect in antiferromagnetic crystals

Magnetoelectric experiments provide information on spin configurations, critical indices and microscopic ionic interactions. The basic theory of the magnetoelectric effect in antiferromagnets is rederived in this article and extended to situations in which there is an external magnetic field including the spin-flop phase. It is found that measurements of the magnetoelectric tensor α as a function of field in the antiferromagnetic and spin-flop phases of an antiferromagnet can provide more complete information in all three categories above. Certain higher-order terms are examined and it is found that it is possible to measure the staggered susceptibility directly in magnetoelectric materials. It is shown that a non-zero value of α causes a tetragonal antiferromagnet to be optically biaxial. A pedagogical discussion of the origins of magnetoelectric effects is given in the Appendix.     

Magnetoelectric effect in one-dimensional metallic conductors

The effect of a transverse magnetic field on a one-dimensional metallic current carrying conductor is considered. The field produces a transverse electric polarization which is wavevector dependent, and which causes a transverse magnetoelectric field. The magnitude of the effect is estimated for typical one dimensional conductors.     

Magnetoelectric effect in a magnetostrictive-piezoelectric bilayer structure

The results of theoretical and experimental investigations of the magnetoelectric effect in a magnetostrictive-piezoelectric bilayer structure have been presented. The expression for the magnetoelectric voltage coefficient in the region of electromechanical resonance has been derived based on the joint solution of the equations of motion for the magnetostrictive and piezoelectric media and the constitutive relations. The dependence of the magnitude of the effect on the thickness of the ferrite and piezoelectric layers has been analyzed. The experimental results for nickel-lead zirconate-titanate bilayer structures have been reported. The theoretical results agree perfectly with the experimental data.     

Thermovoltaic effect in samarium sulfide-based heterostructures

The thermovoltaic effect in samarium sulfide-based bulk heterostructures with compositions Sm_{1 − x} Eu _x S and Sm_{1 − x} Gd _x S is considered in the temperature interval 300–460 K. It is shown that this effect can be observed when an external temperature gradient is absent, i.e., when the sample temperatures near the contacts from which a generated voltage is tapped off are the same. The temperature is measured with thermocouples and also by a contactless method using a thermal imager.     

Dynamic magnetoelectric effect in terbium molybdate

The electric polarization induced in ferroelectric terbium molybdate by a magnetic field linearly varying with time is measured. The measurements are performed in fields up to 19 T at different specified rates of change in the magnetic field at temperatures of 273 and 219 K. The results obtained indicate that there are magnetoelectric effects of two types. One of them is a conventional magnetoelectric effect, which is appropriately referred to as the static magnetoelectric effect. The other effect is characterized by the fact that the electric polarization increases with an increase in the rate of change in the magnetic field and relaxes with time to zero at a fixed nonzero field. This phenomenon is termed the dynamic magnetoelectric effect.     

Magnetoelectric effect in amorphous FeNiSiC ferromagnet-piezoelectric planar structures

The magnetoelectric (ME) effect is studied in composite two- and three-layer disk structures containing magnetostriction layers of an amorphous FeNiSiC ferromagnet and a lead zirconate titanate piezoelectric layer. Due to a high magnetostriction (∼33 × 10⁻⁶) and a low saturation field (∼200 Oe), an FeNiSiC layer has a high piezomagentic coefficient, which results in an effective ME coupling in low fields (∼25 Oe). The ME effect is ∼0.2 V cm⁻¹ Oe⁻¹ at a low frequency and increases to 11.9 and 13.2 V cm⁻¹ Oe⁻¹ when bending and in-plane mechanical vibrations are excited in a resonance manner in the structures at frequencies of ∼8.2 and ∼170.0 kHz, respectively. Structures containing amorphous FeNiSiC layers are promising for magnetic field transducers and electric energy generators and converters.     

Heating-induced endothermal effect in semiconducting samarium sulfide

The effect of heat absorption is revealed in the temperature range where the thermovoltaic effect occurs in single-crystal samarium sulfide (SmS). It is shown that the heat absorption is caused by the collective injection of electrons from donor levels into the conduction band.     

Magnetoelectric effect in an asymmetric layered magnet-piezoelectric structure

The magnetoelectric effect in magnet-piezoelectric layered composite structures is discussed. The magnetoelectric voltage and the magnetoelectric coefficient are calculated taking into account bending deformations that accompany tensile and compressive strains in structures with asymmetric positions of magnetic layers relative to the neutral plane. It is demonstrated that bending deformations lead to a nonuniform distribution of the electric field over the thickness of the piezoelectric layer and to a nonmonotonic dependence of the magnetoelectric coefficient on the thickness ratio of the layers in the structure.     

Anisotropy of the magnetoelectric effect in terbium molybdate

Anisotropy of the nonlinear magnetoelectric effect in a single-crystal, single-domain sample of the β′ metastable ferroelectric paramagnetic phase of terbium molybdate Tb₂(MoO₄)₃ was studied experimentally in dc magnetic fields of up to 6 T at temperatures of 4.2 and 1.8 K. It was shown that the existing models of the magnetoelectric effect cannot explain the experimental dependences of magnetic field-induced electric polarization on the direction of the applied magnetic field. A model of the magnetoelectric effect is proposed that qualitatively describes the observed angular dependence of the magnetic field-induced electric polarization.     

Magnetoelectric effect in multilayer ferromagnetic-piezoelectric structures and its application in electronics

Magnetoelectric effect in multilayer structures composed of magnetostrictive and piezoelectric layers, materials and technologies used to fabricate these structures, and the results of studying the magnetoelectric effect in them are considered. Magnetic field sensors, transformers, and voltage generators based on the magnetoelectric effect in multilayer structures are described.     

Magnetoelectric effect in thin-film magnetostriction-piezoelectric structures grown on a substrate

The theory of the magnetoelectric effect in a thin magnetoelectric film-passive substrate structure is presented. Based on the simultaneous solution of the constitutive equations and the equations of motion for the film and substrate, the dispersion law has been derived for elastic waves propagating in the sample plane. It has been shown that the elastic vibrations in the substrate propagate in a near-surface layer if the velocity of propagation of elastic vibrations in the substrate is higher than that in the magnetoelectric film. In this case, the substrate thickness almost does not influence the magnitude of the effect.     

Magnetoelectric effect in bilayer magnetostrictive-piezoelectric structure. Theory and experiment

Bilayer magnetostrictive-piezoelectric structures have certain advantages compared to bulk composites and this allows us to consider them as perspective materials for the development of devices based on the magnetoelectric effect. The theory of magnetoelectric effect in bilayer magnetostrictive-piezoelectric structure is presented taking into account the thickness dependence amplitude of the mechanical oscillations for the structures in form of rectangular plate. The equation for frequency dependence of the ME effect in the region on the electromechanical resonance was obtained, using motion equation, elastodynamics and electrostatic equations for the magnetostrictive, piezoelectric phases and taking into account the boundary conditions on the interface. The cases of longitudinal and transverse orientations of the electric and magnetic fields were considered. It is shown that the thickness dependence of the ME voltage coefficient has the maximum. The dependence between frequency and the thickness ratio of the layers is presented for both the theory and experiment.     

Magnetoelectric effect in perovskite quantum paraelectric EuTiO3

On the basis of successful theoretical explanation of the observed large magnetic-field effect (by ∼7% with 1.5 T) on the dielectric constant below the Néel temperature T_N of 5.5 K, we have demonstrated convincingly the magnetoelectric effect in an antiferromagnetic quantum paraelectric EuTiO₃ system. The mutual control of electric and magnetic properties is revealed by the variation of the electric-field-induced polarization with applied magnetic fields as well as the change of the magnetic-field-induced spin moments under the control of electric fields. It is found that the applied electric field (magnetic field) acts like a fictitious magnetic field (electric field) on the EuTiO₃ system. The magnetoelectric susceptibility is deduced to be proportional to the product of the magnetization, electrical polarization, magnetic susceptibility and dielectric susceptibility.     

Magnetoelectric effect in composites of magnet,metal-cap,and piezoceramic

We report on the magnetoelectric (ME) effect in three-phase magnet-metal-cap-piezoceramic composites of a thickness-polarized Pb(Zr,Ti)O₃ disk bonded between two truncated conical brass caps and two thickness-magnetized NdFeB magnets along the thickness direction. The effect originated from the product of the magnetic attractive–repellent effect in the magnets and the amplified piezoelectric effect in the cap-disk assembly. The composites exhibited a ME voltage coefficient α_V of ∼2.6 mV/Oe in the non-resonance frequency range of 0.1–10 kHz with good voltage-field linearity in the field range of 10^-3–10 Oe, besides an enhanced α_V of 167.4 mV/Oe at a resonance frequency of 14.4 kHz. Compared to conventional two-phase and three-phase magnetostrictive material-contained ME composites, these composites possessed two distinct benefits of higher property-tailorable flexibility and requiring no external dc bias magnetic field to enable an obvious α_V. PACS 77.84.-S; 75.80.+q; 77.84.Dy; 77.65.-j; 85.80.Jm     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Magnetoelectric gyrator

The magnetoelectric (ME) gyrator is a device that can convert not only active and reactive impedances, but also current and voltage. In this work, we have carried out research on three gyrators structures based on Terfenol-D/PZT/Terfenol-D, Metglas/PZT/Metglas and Nickel/PZT/Nickel. Detailed investigations of the ME gyrator based on these trilayer composite structures have been performed at the electromechanical resonance frequency.     

过渡族元素掺杂BaTiO3-Tb1-xDyxFe2-y层状复合材料中的磁电效应

用溶胶-凝胶法制备1.0%mol Mn,Cr,Co掺杂BaTiO3(BTO)粉体,在1350℃下烧结成多晶陶瓷样品.X射线衍射和差示扫描量热分析表明,室温下掺杂BaTiO3具有四方钙钛矿结构;居里点和相变潜热随Cr,Mn,Co掺杂逐渐降低.将掺杂BaTiO3与Tb1-xDyxFe2-y(TDF)胶合制成双层磁电复合材料,并研究了Cr:BTO-TDF,Mn:BTO-TDF,Co:BTO-TDF层状复合材料中的磁电效应.实验表明,在340×80 A·m-1偏置磁场下,Cr:BTO-TDF的横向磁电电压系数达到最大值586 mV·cm-1·(80 A·m-1-1.在400×80 A·m-1偏置磁场下,Mn:BTO-TDF和Co:BTO-TDF的横向磁电电压系数的最大值分别为480 mV·cm-1·(80 A·m-1-1和445 mV·cm-1·(80 A·m-1-1.研究表明掺杂BaTiO3-TDF层状复合材料中具有较强的磁电耦合.作为无铅压电材料,掺杂BaTiO3制备的磁电效应器件颇具应用前景.     

Magnetoelectric gradiometer

Gradiometer resembles in functionality a sensor measuring the magnetic field gradient whose sensitivity is determined the ability to quantify change with respect to base value. Magnetoelectric (ME) gradiometer designed in this study utilizes ME composites with ring-dot piezoelectric transformer structure working near electromechanical resonance, where ring acts as the input while dot acts as the output. Magnetostrictive disc was bonded on top of the output section resembling a bilayer composite structure. The resonance frequency of sample was found to be in the range of 91–94 kHz. The generated magnetic field due to converse ME effect interacts with the externally applied magnetic field producing flux gradient which is detected through the frequency shift and output voltage change of gradiometer. The measurements clearly illustrate that the proposed design has high sensitivity and it can be used for detecting magnetic field gradient.     

Magnetoelectric effect and magnetic dynamics in the Gd2CuO4 antiferromagnet

The magnetoelectric effect and the magnetic dynamics in Gd₂CuO₄ have been studied using a phenomenological approach and group-theory methods. Vector order parameters are introduced based on four magnetic sublattices. Invariant products of the order parameters are determined, from which the thermodynamic potential density is constructed. Using the spin-wave representation, the calculations can be significantly simplified and the ground orientation magnetic state can be presumably determined. The magnetic dynamics is described by the Landau-Lifshitz equations, from which the antiferromagnetic resonance frequency and the dynamic susceptibilities, namely, magnetic, antiferromagnetic, magnetoelectric, and antiferroelectric susceptibilities are found. The frequency and the susceptibility are shown to be controlled by applied electric field.