Direction Of Electric Polarization Research Articles

Ferroelectric control of ferromagnetism in CrTeI/In2Se3 heterostructure: A first-principles study

Ferromagnetic/ferroelectric heterostructures provide an effective avenue for designing new functional materials with novel properties by combining the advantages of different materials. In this context, we investigate systematically the structure, electronic properties, and ferromagnetism of CrTeI/In2Se3 heterostructures using the first-principles calculations. Through the incorporation of the ferroelectric In2Se3, we modulate the magnetocrystalline anisotropy, exchange interactions, Dzyaloshinskii-Moriya interaction, and other key magnetic parameters of the ferromagnetic CrTeI. Consequently, the easy magnetization direction can be reorientated from in-plane to out-of-plane by switching the electric polarization direction. The enhancement of ferromagnetic coupling and the weakening of antiferromagnetic coupling raise the Curie temperature significantly. Simultaneously, the modulation of the magnetic parameters refines the conditions for forming skyrmions in the heterostructures. The findings in this work hold reference value for understanding the ferroelectric control of ferromagnetism and benefit the applications of two dimensional magnetic materials in spintronics.

Large and nonlinear electric field response in a two-dimensional ferroelectric Rashba material

The achievement of electrical spin control is highly desirable. One promising strategy involves electrically modulating the Rashba spin orbital coupling effect in materials. A semiconductor with high sensitivity in its Rashba constant to external electric fields holds great potential for short channel lengths in spin field-effect transistors, which is crucial for preserving spin coherence and enhancing integration density. Hence, two-dimensional (2D) Rashba semiconductors with large Rashba constants and significant electric field responses are highly desirable. Herein, by employing first-principles calculations, we design a thermodynamically stable 2D Rashba semiconductor, YSbTe<sub>3</sub>, which possesses an indirect band gap of 1.04 eV, a large Rashba constant of 1.54 eV·Å and a strong electric field response of up to 4.80 e·Å<sup>2</sup>. In particular, the Rashba constant dependence on the electric field shows an unusual nonlinear relationship. At the same time, YSbTe<sub>3</sub> has been identified as a 2D ferroelectric material with a moderate polarization switching energy barrier (~ 0.33 eV per formula). By changing the electric polarization direction, the Rashba spin texture of YSbTe<sub>3</sub> can be reversed. These outstanding properties make the ferroelectric Rashba semiconductor YSbTe<sub>3</sub> quite promising for spintronic applications.

Electronic and Magneto-Electric properties of YFeO3

In this study, we have thoroughly investigated the electronic, magnetic, and electrical properties of yttrium orthoferrite using density functional theory (DFT) within the generalized gradient approximation (GGA) and the (GGA + U) approach, which incorporates the Hubbard term (U). Both approximations consistently reveal a semiconductor behavior and an antiferromagnetic behavior of type-G between the iron (Fe) ions. To delve deeper into the magnetic interactions within YFeO3, we have proposed a physical model. This model allows us to calculate the magnetic exchange coupling and magnetic anisotropy parameters through DFT calculations. Additionally, we have conducted computations to determine the electric polarization. Our results have shown that the electric polarization in YFeO3 is exclusively derived from electronic polarization. We have also explored the relationship between the direction of electric polarization and the easy-axis magnetization. In our investigation, we found that both the electric polarization and easy-axis magnetization align along the c-axis in both approximations. Furthermore, we have examined the influence of the Hubbard term on the direction of polarization. To assess the magnetic temperature transition, we employed Monte Carlo simulations using the Ising model. The critical temperature, denoted as TN, obtained with the GGA approximation is found to be 726.66 K. Remarkably, this value closely matches the experimental critical temperature when compared to the critical temperature obtained with the GGA + U approximation.

Intrinsic multiferroicity and magnetoelectric coupling in VSI2 monolayer

Two dimensional (2D) multiferroic materials have great potential for miniaturized electronic and high-density multi-states data storage devices due to the coexistence of electric and spin polarization. Because the origins of magnetism and ferroelectricity are mutually exclusive and difficult to coexist, there are still rare to date 2D multiferroic semiconductors with good performance. Here, we propose a 2D multiferroic material, VSI2 monolayer, which has both ferromagnetic and ferroelectric properties by first principles calculation. It shows robust ferroelectricity with an appropriate switching barrier (∼140 meV), and the in-plane ferroelectric polarization is 1.44 × 10−10 C/m. At the same time, the VSI2 monolayer magnetic easy axis is along the b-axis direction and owns a large magnetic anisotropy energy (MAE) (512 μeV/V-ion). Based on Monte Carlo simulations of the Heisenberg model, the Curie temperature (TC) is calculated to be approximately 92 K. In addition, biaxial strain can significantly change the MAE, and the in-plane magnetic easy axis can be switched to the out-of-plane direction by 5% biaxial tensile strain. In particular, we can change the magnetic moment at the two ends of VSI2 nanoribbons by switching the direction of electric polarization, providing an opportunity for the application of magnetic-electric control and memory devices. Our theoretical prediction provides a good platform for studying the 2D multiferroic effects and spintronic properties.

New ( αβγ )-incommensurate magnetic phase discovered in the MnCr2O4 spinel at low temperatures

The nuclear and magnetic structure of the spinel $\mathrm{Mn}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ is reinvestigated by magnetization, specific heat, and neutron diffraction experiments at different temperatures. Four samples of this spinel synthesized under different atmospheres are analyzed. Through these experiments, a new magnetic phase, with propagation vector ${\stackrel{P\vec}{k}}_{\mathrm{I}2}=(0.6597(1)\phantom{\rule{0.16em}{0ex}}0.5999(1)\phantom{\rule{0.16em}{0ex}}0.1996(2))$, not previously reported, is identified below 18 K when the sample is synthesized under a reductive atmosphere. A possible explanation for the different magnetic ground states observed is given based on the competition among the main exchange interactions present in the system. Using the magnetic superspace group formalism, the symmetry of the nuclear and magnetic structures is determined. The presence of transverse conical magnetic structures in the lower-temperature phases allows for multiferroicity in this compound, and the electric polarization direction is determined for each magnetic phase.

Two-Dimensional Ferroelectricity in a Single-Atom Adsorbed BiI3 Monolayer

Two-dimensional (2D) ferroelectric materials have received tremendous attention in recent years for their potential applications in high-performance electronic nanodevices, such as ferroelectric random-access memories. To increase the density of a ferroelectric memory, a 2D ferroelectric material with multiple ferroelectric states controllable via an external electric field is needed. However, 2D ferroelectric materials are still rare and most of them only have two equivalent ferroelectric states with opposite electric polarization directions. Here, we propose that a 2D ferroelectric material with multiple ferroelectric states can be realized by single-atom adsorption on a metal halide monolayer. Using first-principles calculations, we demonstrate that the 2D BiI3 monolayer adsorbed by Pd single atoms (denoted as Pd@BiI3) is a stable ferroelectric material, which possesses six equivalent ferroelectric states with different electric polarization directions. These findings provide a potential route to achieve multi-state 2D ferroelectric materials for multi-functional device applications.

Strong Field Enhancement and Unidirectional Scattering Based on Asymmetric Nanoantenna

Dielectric-metal nanostructures have lately emerged as one of the most promising approaches to modulating light at the optical frequency. Their remarkable electric and magnetic resonances give them a one-of-a-kind ability to augment local field enhancements with negligible absorption losses. Here, we propose a hybrid metal-dielectric-metal (MDM) nanoantenna that contains a dimer of three-layers of shell nanoparticles. In addition, we only theoretically and numerically show the optical properties of the hybrid dimer nanoantenna. We found that the nanoantenna sustained unidirectional forward scattering with narrow beamwidth (30.9 deg) and strong scattering intensity (up to 5 times larger than the single MDM particle). Furthermore, when the hybrid asymmetric dimer was excited by the plane wave with different electric polarization directions, our findings revealed that the hybrid nanoantenna boosted the gap’s electric near-field while also supporting unidirectional forward scattering. Finally, we analyzed the hybrid dimer with substrates of different materials. It supported strong electric high-order moments along the z-axis and x-axis in gaps between MDM nanoparticles and between MDM nanoparticles and the Ge substrate, owing to the intense displacement currents inside of the dielectric layer. We found that the local electric field of this MDM hybrid dimer nanoantenna with Ge substrate was well improved and attained 3325 v/m.

Robust ferroelectric-gating-dependent electronic and magnetic properties in a 1T-VSe2/BiAlO3(0001) multiferroic heterostructure

The modulation of magnetism and related electronic properties is highly desirable for advanced nanoscale electronic and spintronic applications, but volatility in electron spin manipulation is a major challenge that requires urgent attention. Here, we use density functional theory (DFT) calculations to show that the electronic and magnetic properties of a ferromagnetic [half-]metallic 1T-VSe2 monolayer can be effectively modulated via ferroelectric BiAlO3(0001) gating. In particular, the carry type in the 1T-VSe2 overlayer can be switched from being n-type to p-type or n+ -type through the reversal of the ferroelectric polarization. The magnetocrystalline anisotropy of the 1T-VSe2 monolayer can also be changed from easy-plane to easy-axis. In addition, the band offset, magnetic moments, exchange interaction, and Curie temperature (Tc) of the 1T-VSe2 overlayer show significant dependence on the electric polarization direction, with the calculated surface magnetoelectric coupling coefficients (αS) reaching 10−10 G cm [2]/V. This demonstration of robust ferroelectric-gating-dependent magnetism and related electronic properties holds great promise for the innovative design and implementation of next-generation nanoscale non-volatile ultra-low power devices.

Strong magnetoelectric coupling at an atomic nonmagnetic electromagnetic probe in bismuth ferrite

Isolated nonmagnetic substitutional defect ions experience huge coupled electric magnetic interaction in the single-phase multiferroic ${\mathrm{BiFeO}}_{3}$. In the ferroelectric state above the magnetic N\'eel temperature ${T}_{N}$, the electric environment generates a single symmetric electric field gradient (EFG) parallel to the electric polarization direction. Below ${T}_{N}$, a distinct magnetic interaction arises, monitored by the probe nuclei via their magnetic moment. Two magnetic environments arise, given by the relative angle of the local magnetic moment within its easy magnetic plane with respect to the EFG orientation. The angle between field gradient orientation and magnetic field direction is the most stable fitting parameter. The magnetic interaction concomitantly increases the EFG dramatically which reflects an outstandingly large local magnetoelectric coupling. In the set of best fits, two different electric environments form concurrently with two distinctly different local magnetic fields. The magnetic ordering in ${\mathrm{BiFeO}}_{3}$ thus completely distorts the electric environment of the nonmagnetic probe nucleus. The implications for the local effect of dopants in ${\mathrm{BiFeO}}_{3}$ are discussed. A third probe environment arising independent of temperature is identified and associated with an iron vacancy.

Giant magnetoresistance and tunneling electroresistance in multiferroic tunnel junctions with 2D ferroelectrics.

Multiferroic tunneling junctions (MFTJs), composed of two magnetic electrodes separated by an ultrathin ferroelectric (FE) thin film as a barrier, have received great attention in multi-functional devices. Recent theoretical and experimental works have revealed that ferroelectric polarization exists at room temperature in two-dimensional ferroelectric (2D FE) materials within the ultrathin thickness. Here we propose a novel MFTJ Ni/bilayer In2Se3/BN/Ni, in which the resistance of the tunneling spin polarization electrons can be modulated by different magnetization alignments of the electrode and electric polarization direction of the 2D FE In2Se3 layer, leading to multiple tunneling resistance states. The tunneling magnetoresistance (TMR) and electroresistance (TER) of MFTJs are enhanced by the inserted h-BN layer, achieving an ON/OFF TER ratio of 4188% as well as a TMR ratio of 581% with a much lower resistance area. The giant tunneling resistance ratio, multiple resistance states, and ultra-low energy consumption in 2D FE-based MFTJs suggest their great potential in non-destructive non-volatile memories.

Heat capacity anomaly near magnetic phase transition in GaFeO3

A heat capacity anomaly in the vicinity of magnetic transition was observed in single crystal GaFeO3 for the first time. The crystals grown along the expected electric polarization direction were characterized by X-ray diffraction, Mössbauer and magnetic measurements. Two separate data analyses of heat capacity showed similar results within the experimental accuracy. Critical exponent, α=-0.2(1), and amplitude ratios of positive and negative reduced temperatures near the critical point, A+/A-=1.2(1), are consistent with behavior of a 3-D Heisenberg ferromagnet.

Low magnetic-field induced high temperature dynamic magnetoelectric coupling performances in Z-type Sr3Co2Fe24O41

Magnetic-field induced dynamic magnetoelectric coupling effects and polarization performance of Z-type Sr3Co2Fe24O41 (SCFO) ceramic has been investigated. Results found that SCFO’s transverse tapered magnetic structure can induce electric polarization, and its electric polarization direction will not change under external magnetic effects. First-order dynamic magnetoelectric coupling coefficient (α) and second-order dynamic magnetoelectric coupling coefficient (β) of SCFO exhibited strong response main in magnetic structural phase transition region. The magnetoelectric structural phase transition position appeared in low magnetic field, and the magnetic moment vector and its corresponding electric polarization vector of SCFO exhibited the most unstable state near its equilibrium position, which is beneficial for inducing strong dynamic magnetoelectric coupling response. When the applied magnetic fields to SCFO increased, the magnetic moment stability near the equilibrium position increased, and the dynamic magnetoelectric coupling response decreased. Results showed that the dynamic magnetoelectric coupling response of SCFO can bear T 1 = 370 K high temperature. The dynamic magnetoelectric coupling response induced by low magnetic fields in SCFO contributes to its actual application in next generation magnetoelectric information storage devices.

Writing of strain-controlled multiferroic ribbons into MnWO4

Local and low-dimensional structures, such as interfaces, domain walls and structural defects, may exhibit physical properties different from the bulk. Therein, a wide variety of local phases were discovered including conductive interfaces, sheet superconductivity, and magnetoelectric domain walls. The confinement of combined magnetic and electric orders to spatially selected regions may be particularly relevant for future technological applications because it may serve as basis of electrically controllable magnetic memory devices. However, direct observation of magnetoelectric low-dimensional structures cannot readily be done partly because of the lack of experimental techniques locally probing their physical nature. Here, we report an observation of multiferroic ribbon-like domains in a non-multiferroic environment in MnWO4. Using optical second harmonic generation imaging, we reveal that a multiferroic phase is stabilized by locally generated strain while the bulk magnetic structure is non-multiferroic. We further find that the confined multiferroic state retains domains with different directions of electric polarization and we demonstrate deterministic writing of a multiferroic state embedded in a non-multiferroic environment.

Electric polarization tune enhanced photoelectrochemical performance of visible light active ferroelectric Bi0.5Na0.5TiO3 nanostructure photoanode

Significantly enhanced photoelectrochemical (PEC) performance of the visible light active photoanodes of ferroelectric Bi0.5Na0.5TiO3 nanostructure has been demonstrated by tuning the electrical polarization of the film. The photocurrent density of unpoled Bi0.5Na0.5TiO3 photoanode increases from 0.48 mA cm−2 at 1 V with respect to Ag/AgCl to 1.21 mA cm−2 after negative poling, whereas it decreases to 0.18 mA cm−2 after positive poling. The incident photon-to-current conversion efficiency (IPCE) of the nanostructure photoanodes has been observed to vary from 5% to 28% just by changing the direction of electric polarization. The change in the PEC performance and enhancement in the IPCE value after switching the polarization state of Bi0.5Na0.5TiO3 photoanodes have been attributed to the modification in the band bending at the interface of semiconductor electrode/electrolyte, leading to facilitate the increment in photogenerated charge transfer efficiency. The modulation in the band bending and variation in the charge transfer method after switching the polarization state are confirmed by Mott-Schottky (M-S) and electrochemical impedance spectroscopy (EIS) measurements. Our work provides a new visible light active ferroelectric nanostructure material for efficient visible light active photoelectrochemical performance.

Orbital-hybridization-created optical excitations in Li2GeO3

The three-dimensional ternary Li2GeO3 compound presents various unusual essential properties. The main features are thoroughly explored from the first-principles calculations. The concise pictures, the critical orbital hybridizations in Li–O and Ge–O bonds, are clearly examined through the optimal geometric structure, the atom-dominated electronic energy spectrum, the spatial charge densities, the atom and orbital-decomposed van Hove singularities, and the strong optical responses. The unusual optical transitions cover the red-shift optical gap, various frequency-dependent absorption structures and the most prominent plasmon mode in terms of the dielectric functions, energy loss functions, reflectance spectra, and absorption coefficients. Optical excitations, depending on the directions of electric polarization, are strongly affected by excitonic effects. The close combinations of electronic and optical properties can identify a significant orbital hybridization for each available excitation channel. The developed theoretical framework will be very useful in fully understanding the diverse phenomena of other emergent materials.

Terahertz emission spectrum of polar antiferromagnet Fe<sub>2</sub>Mo<sub>3</sub>O<sub>8</sub>

In polar materials, the transition of electrons in momentum space will change the spontaneous polarization. When excited by femtosecond pulse laser, the transient modulation of the electric polarization will radiate electromagnetic wave at terahertz frequency. In a magnetic ordered system, the coherent excited spin wave radiates electromagnetic waves of the same frequency in the process of precession and relaxation. The investigation of the terahertz emission spectra of these materials not only helps us to understand the ferroelectric and magnetic ordered dynamic processes of materials, but also provides a reference for searching for new terahertz sources. We study the terahertz emission spectrum of the polar antiferromagnet Fe<sub>2</sub>Mo<sub>3</sub>O<sub>8</sub>. Under the pumping of 800 nm laser, electrons in the material are excited across the band gap leading the electric polarization to be ultra-fast modulated. The broadband terahertz excitation spectrum from 0.1 to 3.5 THz is observed, and the direction of the terahertz electric field is along the inherent electric polarization direction of the material. After entering into the magnetic order state, two new single-frequency terahertz oscillations are observed, located at 1.25 THz and 2.7 THz respectively, which correspond to the excitation of the two antiferromagnetic spin waves of Fe<sub>2</sub>Mo<sub>3</sub>O<sub>8</sub>.

Bulk Photovoltaic Effect in a Pair of Chiral-Polar Layered Perovskite-Type Lead Iodides Altered by Chirality of Organic Cations.

The bulk photovoltaic effect (BPVE) is a promising optoelectronic phenomenon for generating a steady-state photocurrent without a bias voltage. Nevertheless, the simple and rational design of materials exhibiting the BPVE remains an important topic in the relevant fields. Here, we report the observation of the BPVE in a simple chiral-polar pair of layered perovskite-type lead iodides in the crystal space group of P1 (#1), which were synthesized by assembling R- and S-chiral organic cations, respectively. The sign of the zero-bias photocurrent is altered by the R/S-chirality of the assembled cations, which define the direction of electric polarization derived from the electric dipole moment of each chiral organic cation aligned in a crystal. The strategy of chirality control in a crystal is expected to be useful when searching for BPVE materials.

New physical insight in structural and electronic properties of InSb nano-sheet being rolled up into single-wall nanotubes

The structure evolution and the electronic properties of InSb monolayers and nanotubes were thoroughly studied by first-principles theory. The results showed that InSb monolayer exhibits intrinsic electric polarization of 12 pC/m, and the direction of electric polarization can be switched when strain or external electric fields are applied. InSb monolayer has a high electron and hole-mobility of ~7 × 103 and 0.7 × 102, respectively. When the monolayer is rolled up to form nanotubes, the optimized parameters, energy level, and electronic structure, were calculated for the armchair and the zigzag configurations. The calculated electronic structure shows that the monolayer has a direct band gap of 1.29 eV, while after being rolled up into small diameter InSb [6] and InSb (6,0) nanotubes, there is an increase of the band gap to 1.58 and 1.70 eV for the two aforementioned configurations, respectively. Furthermore, the strain energy of the nanotubes is lower than that of the monolayer. The increase of band gap when the monolayer was rolled up into nanotubes was attributed to p-p coupling between In-3p orbital in the conduction band of InSb in nanotubes. The findings of the present work suggest that InSb monolayer may have observable ferroelectricity; thus, it can qualify for consideration in information storage applications.

Analysis of magnetoelectric states in magnetic fields in DyMnO3

A phenomenological analysis of the experimental phase states of the DyMnO3 ferroelectromagnet with a modulated spin structure in magnetic fields along the X, Y, and Z axes was carried out, taking into account the fourth-order magnetic anisotropy. The possibility of a polarization flop (i.e., reorientation of the direction of electric polarization) is explained only in cases of a magnetic field direction along the X and Y axes. The relative values of the fourth-order magnetic anisotropy parameters consistent with measurements of magnetic moments are found.

Fabrication of high-qualified (Bi1−xBax)FeO3 multiferroic thin films by using a pulsed DC reactive sputtering method and demonstration of magnetization reversal by electric field

(Bi1−xBax)FeO3 multiferroic thin films with ferromagnetism and ferroelectricity were fabricated by a pulsed DC reactive sputtering and applied to create a magnetic domain using an electric field. The (001)-oriented (Bi1−xBax)FeO3 thin films, the electric polarization direction of which is perpendicular to the film plane, were fabricated onto a non-single-crystalline substrate with a Ta seedlayer/(111)-oriented Pt underlayer. A low pulse frequency (long time for sputtering OFF) and a high sputtering power (high-energy deposition) were effective for the acceleration of the crystallization of the (Bi1−xBax)FeO3 phase owing to the enhancement of the surface diffusion of sputtered atoms on the substrate surface. The saturation magnetization of the film was approximately 90 emu/cm3 and the coercivity was approximately 2.5 kOe. Magnetic force microscopy analysis of the (Bi0.48Ba0.52)FeO3 film confirmed that the magnetization was generated by applying only a local electric field. The multiferroic film described here is expected to be useful for electric-field-driven magnetic devices.