Magnetoelectric Properties Research Articles

Kramers nodal lines and Weyl fermions in SmAlSi

Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy connecting time-reversal invariant momenta. KNLs are robust to spin orbit coupling and are inherent to all non-centrosymmetric achiral crystal structures, leading to unusual spin, magneto-electric, and optical properties. However, their existence in in real quantum materials has not been experimentally established. Here we gather the experimental evidence pointing at the presence of KNLs in SmAlSi, a non-centrosymmetric metal that develops incommensurate spin density wave order at low temperature. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and magneto-transport methods, we provide evidence suggesting the presence of KNLs, together with observing Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. We discuss the nesting possibilities regarding the emergent magnetic orders in SmAlSi. Our results provide a solid basis of experimental observations for exploring correlated topology in SmAlSi

Annealing effect on the magneto-electric properties of SOT-MTJs from micro to nano-sized dimensions

Spin–orbit torque magnetic random-access memory exhibits great potential for next-generation memory. Annealing is an essential process for SOT magnetic tunnel junctions (SOT-MTJs) thin films. To optimize the SOT-MTJ thin films, studying the different dimensions from micro-size to nano-size is very necessary. Here, we investigate the annealing effect on magneto-electric properties of micro-scaled and nano-scaled SOT-MTJs. The tunnel magnetoresistance (TMR) and critical current density (J c) increase after annealing, attributing to the improved crystallization of CoFeB layers and perpendicular magnetic anisotropy (PMA), respectively. However, the TMR increment of micro-scaled SOT-MTJ is larger than that in nano-scale, due to the reduced defects of micro-scaled SOT-MTJs by annealing. Additionally, the J c of nano-scaled SOT-MTJ is decoupled from that of micro-scaled SOT-MTJ because of the improved PMA and diminished thermal effect. This work assesses the different annealing effects in micro- and nano-sized dimensions and supplies experiment foundations to optimize the performance of SOT-MTJs.

Magnetoelectric, spectroscopic, optical and elastic properties of Co-doped BaTiO3 ceramics

Magnetoelectric, spectroscopic, optical and elastic properties of Co-doped BaTiO3 ceramics

Unravelling the linear and biquadratic magnetoelectric coupling in Ba0.95Sn0.05Ti0.95 Ga0.05O3 – CoFe1.8Ga0.2O4 particulate multiferroic composites

Since multiferroic composites have substantially stronger magnetoelectric coupling between the order parameters than the single-phase multiferroics, they are more interesting prospects for next-generation multi-state memories and spintronic devices. In light of this, the current work outlines the fabrication of ferroelectric perovskite BaTiO3 and ferrimagnetic spinel CoFe2O4-based particulate multiferroic composites with general formulla (1-x) Ba0.95Sn0.05Ti0.95 Ga0.05O3 – x CoFe1.8Ga0.2O4 (x = 0.04, 0.08 & 0.12). At room temperature, the gallium and tin doping enhanced the dielectric properties of BaTiO3 (ε ´ =9200), and particulate composite (ε ´ =6000) with 12% of CoFe1.8Ga0.2O4 phase. In the same composite, the reduced leakage current density of 3.4 μA/cm2 and improved magnetoelectric properties, with linear and quardatic coupling coefficients of 3.41 mVcm−1Oe−1 and 3.4 × 10−4 mVcm−1Oe−2 were achieved. In composites with a larger magnetic phase, the decrease in cell volume and increased tetragonality produces the compressive strain, that in turn improves the ME coupling. Diffused ferroelectric transitions were ascertained by using the Curie- Weiss Law. Enhanced dielectric properties are linked to decrease in hopping and bond lengths, caused by the incorporation of non-magnetic Ga3+ ions in the CoFe2O4 lattice. A reduction in leakage current density was observed on Sn doping. The calculated square-ness ratios reveal an ordered multi-domain structure. Improved dielectric response along with linear and biquadratic coupling makes these Sn and Ga doped BaTiO3-CoFe2O4 particulate composites as potential candidates for magnetoelectric devices.

Study of Magnetoelectric Properties of Composites Based on Magnetic Particles of Fe2O3 and Bentonite Using Percolation Theory

Study of Magnetoelectric Properties of Composites Based on Magnetic Particles of Fe2O3 and Bentonite Using Percolation Theory

Development of a novel lead free (CoFe1.9Bi0.1O4/BaTi0.89Sn0.11O3/CoFe1.9Bi0.1O4) magnetoelectric composite via new design strategy

A novel lead free ceramic based magnetoelectric (ME) tri-layered composite with new design strategy has been fabricated by using sol-gel synthesized Bi3+ doped CoFe2O4 and Sn4+ doped BaTiO3. Structural, microstructural, magnetostriction, piezoelectric and magnetoelectric properties of the synthesized materials and developed system have been thoroughly investigated. CoFe1.9Bi0.1O4 have shown the improvement of magnetostriction (∼259 ppm) and strain sensitivity (∼323 ×10−9 Oe−1) compared to those of un-doped CoFe2O4 (magnetostriction ∼163 ppm and strain sensitivity ∼99 ×10−9 Oe−1). On the other hand, the piezoelectricity of BaTi0.89Sn0.11O3 has improved to 424 pC/N from a value of 194 pC/N for un-doped BaTiO3. The unique design strategy (where the output signal has been collected directly from the piezoelectric layer) and the simultaneous improvement of both the magnetostriction and piezoelectricity of the corresponding components have helped in achieving high ME coupling in the final device. The achievement of high values of in-plane ME coupling coefficients (αME) (α31) at off-resonance and zero-bias resonance conditions (αME ∼49 and 750 mV.cm−1. Oe−1, respectively) have proven the ability of the fabricated device in various potential applications related to magnetic field sensing and magnetoelectric effect.

Magnetoelectric Properties of Lead-Free Three-Layer Structure Barium–Titanate–Piezoceramic Nickel

The results of the comprehensive magnetoelectric interaction research in three-layer structure Ni–piezoceramic BaTiO3–Ni are presented. It has been theoretically shown and experimentally confirmed that, in the general case, the dependence of the magnetoelectric response has non-linear character. At low bias magnetic field, a quadratic dependence magnetoelectric response from an AC magnetic field is observed then there is a linear section, as well as at high values of the field magnetoelectric response has saturation. The obtained values of the magnetoelectric characteristics (αEmax = 32 V(cmOe) for resonance and 437 mV/(cmOe) for field dependence) for lead-free three-layer structure barium–titanate–piezoceramic nickel are comparable with the magnetoelectric characteristics for similar structures, based on lead-containing ceramics.

Tailing the Magnetoelectric Properties of Cr2Ge2Te6 by Engineering Covalently Bonded Cr Self-Intercalation: Ferromagnetic Half-Metal

Two-dimensional intrinsic ferromagnetic half-metals (HMs) are important for spintronics. Based on a systematic research of CrGeTe3 (CGT) bilayers and multilayers with the self-intercalated (SI) Cr (CrSI) atom, we find that self-intercalation can enhance interlayer magnetic coupling, which results in a super-exchange interaction between interlayers. The CGT bilayer keeps half-metallicity with the interlayer ferromagnetic (FM) order after Cr’s self-intercalation, independent of CrSI atoms’ concentration and stacking orders. Moreover, SI-CGT multilayers with interlayer FM order transform from HMs into normal spin-polarized metals, as the states at the Fermi level increase. Moreover, the magnetic anisotropy energies (MAEs) of SI-CGT-AA and SI-CGT-AB are −0.160 and −0.42 meV/f.u., respectively, which are modulated by the CrSI atoms. The MAEs of SI-CGT-AA and SI-CGT-AB are different, as the hybridization interactions between Cr’s d orbitals are different from each other. SI-CGT bilayers’ magnetic easy axis (EA) switches from the original [001] of CGT to the [100] direction, independent of the stacking orders. It is inferred that the MAE is mainly contributed by the hybridization between Te’s px and py, py and pz orbitals, and that this hybridization interaction is obviously weakened as CrSI atom is inserted. The SI-CGT bilayers and multilayers show good dynamic and thermal stability at 300 and 500 K. These findings offer a promising way to manipulate the interlayer exchange interaction and magnetoelectric properties of CGT multilayers and other vdW magnets.

Spin–Charge Conversion in Hybrid Structure PbZrO3/Y3Fe5O12/Pt

Multifunctional oxide heterostructures exhibiting magnetoelectric properties show great potential in advanced applications which are attracting a number of recent investigations. Herein, hybrid structures are presented including the antiferroelectricity film PbZrO3 (PZO) and the ferrimagnetic insulator (FMI) yttrium iron garnet (Y3Fe5O12, (YIG)) film by means of pulse laser deposition and magnetron sputtering, respectively. A visible double ferroelectricity hysteresis loop for PZO at low electrical field and the distinct X‐ray magnetic circular dichroism (XMCD) spectra for YIG are obtained. To study the spin current transfer processes between platinum (Pt) and the PZO/YIG system, the Pt film is deposited on the PZO/YIG bilayers as the conversion detector and the spin–charge conversion voltage can be obtained via inverse spin Hall effect (ISHE) under thermal gradient excitation. These results indicate that the hybrid structure PZO/YIG/Pt provides a potential route to realize an electric field control of spin–charge conversion and is instructive for future low‐power multiferroic heterostructures‐based spintronic devices.

Polarons: Energetics and their structural and electronic effects in ATiO3 perovskite systems

Understanding the formation of a polaron near vacancies in oxides is of vital importance for controlling defect properties and related functionalities. We examine the energetics and local structure of polarons in the vicinity of oxygen vacancies using density functional theory with the Hubbard on-site Coulombic correction. We systematically consider several $\mathrm{ATi}{\mathrm{O}}_{3}$ perovskite systems: cubic $\mathrm{SrTi}{\mathrm{O}}_{3}$ (c-STO), cubic $\mathrm{BaTi}{\mathrm{O}}_{3}$ (c-BTO), cubic $\mathrm{PbTi}{\mathrm{O}}_{3}$ (c-PTO), tetragonal $\mathrm{BaTi}{\mathrm{O}}_{3}$ (t-BTO), and tetragonal $\mathrm{PbTi}{\mathrm{O}}_{3}$ (t-PTO). The polaron formation energies vary by several orders of magnitude across the systems, where PTO systems have large polaron formation energies $(\ensuremath{\sim}\ensuremath{-}1.688\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$, c-BTO is intermediate (\ensuremath{-}0.234 eV), and c-STO and t-BTO have considerably smaller formation energies $(<\ensuremath{-}0.01\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$. The formation of a polaron is found to influence the charge density, atomic displacement, and electronic structure, with higher polaron energies corresponding to larger charge density changes and greater displacements of the ions surrounding the oxygen vacancy, especially the displacement of the first nearest neighbor A-site. Finally, a comparison of the projected band structures shows fictitious in-gap states present in the delocalized picture of the system moving to the conduction and valence bands in the polaron solution of the system, indicating an incompleteness of the description of a vacancy without considering charge localization as in the polaron picture. In this paper, we provide fundamental properties of polarons near vacancies, which can be used to control and tune defect, charge transport, magnetoelectric, and multiferroic properties of perovskite oxides.

Multicaloric effect in metamagnetoelectric linarite spin chain PbCuSO4(OH)2

The cross response of magnetic and electric fields on the ribbon CuO2 spin chain is used to investigate the multicaloric properties of linarite PbCuSO4(OH)2. The theory is built on a frustrated Heisenberg scheme. Following the magnetoelectric properties, the thermodynamic and caloric coefficients report multiple field–dependent criticalities attributed to the metamagnetoelectric effect. The isentropes of PbCuSO4(OH)2 particularly exhibit about five and six major sharper dips in magnetic and electric field sweeps respectively. This corresponds to the metamagnetoelectric transitions which in turn come along with a large temperature change in the entropy and heat capacity analyses and then increasing the cooling ability of linarite. Further analysis of the magnetocaloric as well as the electrocaloric effects shows a significant growth during the metamagnetoelectric transitions. A clear relationship is established between the magnetoelectric coupling constant, the magnetocaloric and the pyroelectric coefficients, witnessing the metamagnetoelectric transitions-driven multicaloric effect in PbCuSO4(OH)2. Obviously, the resulting total adiabatic temperature change expressed through the magnetocaloric or the pyroelectric coefficient depends on the sign of the magnetoelectric coupling constant. Therefore, the occurrence of the metamagnetoelectric effect with several magnetic and electric field-dependent transitions characterized by a set of positive and negative increases in the magnetoelectric coupling provides a great advantage by increasing the possibilities of a significant multicaloric effect in the linarite PbCuSO4(OH)2 cuprate spin chain.

Nontrivial spin textures induced remarkable topological Hall effect and extraordinary magnetoresistance in kagome magnet TmMn6Sn6

Kagome magnets RMn6Sn6 (R = lanthanides) manifest novel topological phases and field-induced transitions, owing to the interplay between strong correlations and geometrical frustration among the corner-sharing-triangle intralayers. Here we report the magnetometry and magnetoelectric transport properties of TmMn6Sn6 single crystal, which coexists with Tm and Mn magnetic sublattices. We reveal that this compound displays multiple magnetic structures with the increase of in-plane magnetic field. The combination of non-collinear magnetic structure and real-space Berry curvature leads to a remarkable topological Hall effect over an extensive temperature range. The in-plane magnetic transition is accompanied by a large magnetoresistance effect of -32 ∼ -17% from 10 K to 300 K at 7 T, and the magnetoresistance manifests two peaks with increasing the in-plane field. These observations suggest a robust Mn - Tm magnetic coupling, which provides a nontrivial ferrimagnetic network for the further investigation of new emergent topological magnetic structures.

PCMW2D and 2D Raman correlation spectroscopy evidence for presence of spin-phonon coupling in hexagonal LuMnO3

Two-dimensional correlation spectroscopy (2D-COS) and perturbation-correlation moving window two-dimensional correlation spectroscopy (PCMW2D) analysis are performed on the temperature-dependent Raman spectra of hexagonal LuMnO3 single crystal. Under the resonance with the on-site Mn d-d transitions, the correlation between the phonons which are relate to the vibration of Mn ions’ bonds and spin-excitation peaks suggest a strong spin-phonon coupling in LuMnO3. The PCMW2D results clearly show that the significant change in phonons and spin-excitation peaks occurs around the Néel temperature and the spin reorientation transition. The multiple components in the broad spin-excitation peaks also suggest variations in spin symmetries in the ground state. Furthermore, we propose that the 2D-COS and PCMW2D Raman correlation spectroscopies provide a simple and powerful method for investigating the couplings and the transitions, which would be very important for understanding systematically the magnetoelectric properties of multiferroic materials.

Magnetoelectric properties of CoFe2O4/BNT–BT0.08 biphasic nanocomposites, with 0–3 connectivity, prepared by sol-gel method

Motivated by the goal of developing ultralow power, smart and multifunctional nano (micro) electronic devices, research has shown unwavering interest in synthesis methods, architectures and interphase connectivity of composites containing magnetostrictive and piezoelectric phases, known as magnetoelectric (ME) materials. Herein we report on CoFe2O4/0.92Bi0.5Na0.5TiO3–0.08BaTiO3 biphasic ME composites, obtained by sol-gel chemistry, by mixing the precursor sols of the two phases into one precursor sol and further transforming it into gel, with the goal of obtaining homogeneous nanocomposites with magnetoelectric properties. The structural properties, the temperature dependance of dielectric properties, the magnetic and magnetoelectric properties of these biphasic mixtures, with various molar ratios CoFe2O4/BNT–BT0.08 = 0.5:1, 1:1 and 1.5:1, are investigated. It is observed that the amount of CoFe2O4 and the synthesis in situ of these composites influences their macroscopic properties showing a high difficulty of carrying out an efficient poling resulting in small piezoelectric and magnetoelectric response. It was concluded that the synthesis procedure, the type of architecture and the interphase connectivity are of outmost importance for magnetoelectric properties based on lead-free materials.

Investigation of the Ferroelectric, Magnetic and Magnetoelectric Properties in Honeycomb-Layered YCrTeO6

Investigation of the Ferroelectric, Magnetic and Magnetoelectric Properties in Honeycomb-Layered YCrTeO6

High-pressure single crystal growth and magnetoelectric properties of CdMn7O12

The concurrent presence of large electric polarization and strong magnetoelectric coupling is quite desirable for potential applications of multiferroics. In this paper, we report the growth of CdMn7O12 single crystals by flux method under a high pressure of 8 GPa for the first time. An antiferromagnetic (AFM) order with a polar magnetic point group is found to occur at the onset temperature of T N1 = 88 K (AFM1 phase). As a consequence, the pyroelectric current emerges at T N1 and gradually increases and reaches its maximum at T set = 63 K, at which the AFM1 phase finally settles down. Below T set, CdMn7O12 single crystal exhibits a large ferroelectric polarization up to 2640 µC m−2. Moreover, the spin-induced electric polarization can be readily tuned by applying magnetic fields, giving rise to considerable magnetoelectric coupling effects. Thus, the current CdMn7O12 single crystal acts as a rare multiferroic system where both large polarization and strong magnetoelectric coupling merge concurrently.

Effect of vacuum heat treatment on structural, optical, and magneto-electric properties in Bi-doped Y3Fe5O12 ceramics

Yttrium iron garnet (YIG; Y3Fe5O12) is an important material in the field of electronics because of its unique magnetic properties. This makes it ideal for use in devices such as microwave filters, amplifiers, sensors, and even magnetic storage devices. It is also used in spintronics, which is the study of the spin of electrons and how it can be manipulated for storage and computation. Additionally, it is highly stable and has low losses when exposed to electromagnetic fields, making it useful in applications such as controlling electric properties with magnetic fields or vice-versa, and magnetic resonance imaging (MRI). Herein, we have prepared YIG and Bi-doped YIG (Bi: YIG: Y2Bi1Fe5O12) nanoparticles (NPs) using the sol–gel auto-combustion method. The obtained garnet powders were sintered at 950 °C both in an air and vacuum environment. We have explored the structural, electrical, optical, magnetic, and magneto-electric (ME) properties of Bi-doped YIG sintered in a vacuum (YBIG-V) and compared it with YIG and Bi-doped YIG sintered in the air (YBIG-A). We found the enhancement in dielectric response, magnetic properties, and the reduction in leakage current for the YBIG-V ceramics than for YBIG-A, YIG ceramics. We have studied the magneto-electric (ME) coupling at room temperature and found that YBIG-V ceramics show the better coupling strength with a maximum coupling coefficient, αME of 354.3 mV/cm-Oe. The dielectric response of these samples significantly varies with the applied magnetic field, which will be positive in Bi-doped YIG ceramics and negative in pure YIG ceramics. Compared to YBIG-A, YBIG-V samples have better variation in dielectric response with the magnetic field, due to which they may be utilized for magnetic field sensing applications. We also observed that the resonance frequency varies with the applied magnetic field, which may be another parameter for field sensing applications. We attribute the enhancement of these properties in YBIG-V sample to the reduction in the average oxygen valency which is 1.63 for YBIG-A and 1.58 for YBIG-V. These values have been determined with the help of X-ray photoelectron emission spectroscopy data.

МАГНИТОЭЛЕКТРИЧЕСКИЕ ЭФФЕКТЫ И НОВЫЕ ЛОГИЧЕСКИЕ УСТРОЙСТВА СПИНТРОНИКИ

The paper discusses new logic spintronic devices and the prospects for the use of perovskite-type multiferroics as working elements of magnetoelectric components. The principle of operation of the considered logical devices is based on the use of two components - a magnetoelectric, in which the magnetic state is recorded due to energy-efficient magnetoelectric interaction, and a spin-orbital component, in which information is read out based on the conversion of spin into charge due to the spin-orbital interaction of electrons; both components are interconnected by a nanoelectrode. When designing new logic spintronic devices, it is necessary to take into account the effectiveness of the mechanisms of ME interactions; features of spin - polarized currents and associated torques influencing magnetic moments; as well as other factors affecting the speed of switching magnetic states and the sensitivity of the device to external agents. Multiferroic materials that are promising for use as elements of ME components of new logic devices must meet a number of requirements, the most significant of which are the magnitude of the magnetoelectric coupling coefficient and the temperature at which ME effects occur. The paper considers representatives of multiferroics with a perovskite structure that meet these conditions, to some extent partially, these are high-temperature multiferroic bismuth ferrite (BiFeO3) and Ruddlesden-Popper structures, in which high-temperature ferroelectric effects are already realized and under certain conditions an ME effect is possible. The crystal structure of these compounds is considered, and the role of crystallographic distortions responsible for the manifestation of magnetoelectric properties is analyzed. Expressions are obtained for the tensor of the magnetoelectric effect as functions of magnetic order parameters, and the fundamental possibility of realizing ME effects in Ruddlesden-Popper structures containing magnetic cations is shown.

Relationship between the Synthesis Method and the Magnetoelectric Properties of Bismuth Sodium-Potassium Titanate/Nickel Cobalt Ferrite Lead-Free Composites

In this work, the influence of the synthesis methods of piezoelectric and magnetostrictive phases on the final properties of the Bi0.5(Na0.8K0.2)0.5TiO3-Ni0.5Co0.5Fe2O4 composites was studied. Different routes were used to individually synthesize each phase, and the composites were prepared using different fractions for each phase. Composites were sintered, and the structural, microstructural, dielectric, and magnetoelectric properties were evaluated. According to the selected synthesis method employed for each phase, different particle sizes and reactivities of the individual phases were obtained. These differences determined the suitable sintering temperature for each set of composites and were responsible for the final properties. In fact, magnetoelectric properties were modulated by the combination of composition and synthesis routes.

Indicatrix of TE and TM- polarized wave velocities in crystal of classes 4mm, 3m, 6mm with magneto-electric effect

This work is devoted to the theoretical study of the laws of propagation of electromagnetic waves of TE and TM polarization in anisotropic media belonging to classes 4mm, 3m, 6mm, etc. having a magnetoelectric effect. The directions of the vectors of the phase and group velocities of the polarization waves TE and TM at the boundary of a uniaxial crystal with magnetoelectric properties are considered. In the analytical form, the values of the directions of the phase and group velocities of the TE and TM waves are indicated, depending on the direction of the wave vector of the incident wave. The consequences of the obtained results for uniaxial crystals in the absence of magnetoelectric properties are discussed. The solution of the tasks set in this paper is based on the use of the matrix method. On its basis, various problems of wave processes in an isotropic elastic medium, electromagnetic waves in crystals, the distribution of coupled elastic and electromagnetic waves in piezoelectric and piezomagnetic media with a magnetoelectric effect were previously considered. In the presence of a magnetoelectric effect for electromagnetic waves propagating through uniaxial crystals, the parameters of the wave vector, phase and group velocities are determined. The obtained results are analyzed for electromagnetic waves propagating through uniaxial crystals in the absence of a magnetoelectric effect. The indicatrices of the wave vectors propagating in the plane and the phase velocities of the TM polarization waves are limited ( 0 ) x z. Based on the Rayleigh equation, the values of the group velocity are obtained. The density of electromagnetic energy fluxes and their components are determined for TE and TM waves. The energy transfer rate and its direction are determined. It is shown that the group velocities and directions obtained from the Rayleigh equation and the Umov-Poynting vector do not coincide.