Multiferroic Oxide Research Articles

Synthesis and characterization of undoped and Co-Doped Bismuth Ferrite nanoparticles for photovoltaic applications

Abstract In this paper, we reported the structural, vibrational, and optical absorption properties of chemically synthesized multiferroic bismuth iron oxide (BiFeO3) (BFO) and cobalt-doped bismuth iron oxide (BFCO) nanoparticles. The nanoparticles were synthesized via sol–gel methods and annealed at 450 °C for a duration of two hours. Characterization was conducted through techniques such as UV–Vis spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM). XRD analysis revealed average crystallite sizes of 19.1 nm and 20.8 nm for BFO and BFCO, respectively, with no secondary phase observed in the cobalt-doped BFO nanoparticles. Structural analysis via XRD indicated a transformation from rhombohedral to orthorhombic symmetry in the doped BFO nanoparticles. The optical band gap energies were determined to be 2.43 eV for BFO and 2.33 eV for BFCO. The reduction in the band gap in BFCO may be help for relevant for the photovoltaic application. FTIR spectroscopy identified characteristic peaks, including the O–H single bond at 3417 cm−1 and vibrations corresponding to metal–oxygen/Fe–O, Bi–O stretching, and O–Fe–O bending vibrations in BFO and BFCO within the spectral range of 400–1000 cm−1. The morphology and crystallinity of these materials were assed using a SEM, revealing a progressively complex arrangement of flower structures in both BFO and BFCO.

Symmetry, magnetic transitions and multiferroic properties of B-site-ordered A2MnB'O6 perovskites (B' = [Co, Ni]).

The presence of magnetic atoms at the A and B sites and the coupling between these two spin subsystems in perovskites gives rise to a variety of exciting effects. In particular this coupling attracts interest from the field of novel multiferroic and magnetoelectric oxides. Moreover, magnetic double perovskites presenting cationic order at the B sites incorporate an additional modulation that can favor symmetry breaking, multiferroic, magnetoelectric and polar phases. Here, we describe the magnetic structures obtained from neutron diffraction and analyze the symmetry properties of well ordered A2MnB'O6 double perovskites with A= Lu, Yb, Tm, Er, Ho, Y, Tb, La0.5Tb0.5, La and B' = Co or Ni. A rich variety of magnetic orders is formed that have been identified and described, and their symmetry properties are discussed in relation to the multiferroic and magnetoelectric properties of the different compounds.

Probing Sub-Unit Cell Polarization Waves in Multiferroic Layered Oxides with EELS

Probing Sub-Unit Cell Polarization Waves in Multiferroic Layered Oxides with EELS

How Can 4D-STEM Inform Atom Probe Experiments? Relating Structure and Composition of Multiferroic Oxides at the Atomic Scale

How Can 4D-STEM Inform Atom Probe Experiments? Relating Structure and Composition of Multiferroic Oxides at the Atomic Scale

Exploring the Possibility of Thermally Assisted Creation and Annihilation of Anti‐Frenkel Defects in a Multiferroic Oxide for Tuning Interfacial Ferroelectricity

AbstractLattice defects such as oxygen vacancies, interstitials, and their complexes are present in crystalline oxide materials. In particular, anti‐Frenkel defects, which refer to charge‐neutral anion vacancy‐interstitial pairs, are strongly coupled with ferroelectric and dielectric properties as electric dipoles. However, in order to observe their macroscopic manifestation, delicate defect controls are required to the extent that electronic and ionic charges are almost completely suppressed. Here, the thermal cycle dependence of dielectric and piezoelectric properties is scrutinized in the strain‐driven morphotropic phase boundaries of multiferroic La‐substituted BiFeO3 thin films. Electrochemical impedance spectroscopy provides the Warburg feature that is considered evidence of the ionic origin. The observations are discussed based on anti‐Frenkel defects that are created or annihilated reversibly by thermal cycles through high‐temperature structural phase transition temperature or magnetic Néel temperature. The defect dipoles are spontaneously aligned by the flexoelectric effect in the phase boundaries inducing a metastable interfacial ferroelectric phase. The findings offer useful insight into defect dipoles.

Dynamic and controlled stretching of macroscopic crystalline membranes towards unprecedented levels

Imposing and controlling strain in materials such as semiconductors or ferroelectrics is a promising way to obtain new or enhance existing properties. Although the field of strain engineering has seen a rapid expansion over the last two decades, straining semiconductor membranes over large areas remains a challenge. A generic way of tuning strain and hence band structure and electric or magnetic properties of any crystalline material can be obtained by compression of a composite structure involving poorly compressible elastomers. Mechanically similar to the principle of a hydraulic press, this work proposes a device and describes analytically a methodology to easily strain macroscopic membranes up to unprecedented values. Using in-situ X-ray diffraction and Raman spectroscopy, we tuned the biaxial strain in silicon membranes up to a value of 2.1 %, paving the way for new studies in the field of strain related physics, from semiconductors to perovskite oxide multiferroics.

First-principles study of structural and electronic properties of multiferroic oxide Mn3TeO6 under high pressure

Abstract Mn3TeO6 (MTO) has been experimentally found to adopt a P21/n structure under high pressure, which exhibits a significantly smaller band gap compared to the atmospheric R3 phase. In this study, we systematically investigate the magnetism, structural phase transition and electronic properties of MTO under high pressure through first-principles calculations. Both R3 and P21/n phases of MTO are antiferromagnetic at zero temperature. The R3 phase transforms to the P21/n phase at 7.58 GPa, accompanied by a considerable volume collapse of about 6.47%. Employing the accurate method that combines DFT+U and G0W0, the calculated band gap of R3 phase at zero pressure is very close to the experimental values, while that of the P21/n phase is significantly overestimated. The main reason for this difference is that the experimental study incorrectly used the Kubelka-Munk plot for the indirect band gap to obtain the band gap of the P21/n phase instead of the Kubelka-Munk plot for the direct band gap. Furthermore, our study reveals that the transition from the R3 phase to the P21/n phase is accompanied by a slight reduction in the band gap.

Er2FeCrO6: Emerging efficient nanomaterials for multiferroics

The present work deals with the rare earth Erbium-based double perovskite. The chemical precipitation route was adopted followed by calcination at 700 °C for the synthesis of Er2FeCrO6 (EFCO). The phase identification was performed using Rietveld refinement. Morphological analysis shows the formation of nanoparticles of EFCO having an average size of ∼15 nm. The M − H curve recorded at 10 K shows the weak ferromagnetic nature of the sample. Temperature variation of magnetization illustrates that EFCO nanoparticles undergo ferromagnetic transition at Tc = 14 K. Temperature-dependent P-E studies display ferroelectric behaviour with a ferroelectric transition temperature (TCE = 453 K) which is beyond room temperature. The simultaneous existence of magnetic and electric orders may introduce EFCO as a new multiferroic oxide and a good alternative to the popular compound BiFeO3.

Exploration and quantification of magnetocaloric effect in EuTiO3 perovskite using extreme learning machine intelligent computational method

Perovskite EuTiO3 is a multi-ferroic titanate oxide material that exhibits huge magnetocaloric effect at low magnetic field without associated hysteresis loss due to the magnetic field and thermal energy. These unique features coupled with the presence of strong coupling existing between spin and lattice as well as the possibility to switch the magnetic ground state between ferromagnetism and anti-ferromagnetism, foster the potentials of this material for magnetocaloric effect based cooling technology application. Maximum magnetic entropy change of perovskite EuTiO3 determines the strength of magnetocaloric effect in the material and ultimately influences the usability of this material for cooling technology. However, experimental measurement of maximum magnetic entropy change is challenging and consumes appreciable resources and time. Maximum magnetic entropy change of intrinsic and doped EuTiO3 perovskite is modeled in this work using extreme learning machine intelligent algorithm (ELMIA) with the ionic radii, elemental concentration and applied magnetic field descriptors. The developed ELMIA-SINE with sine activation function performs better than ELMIA-SIG model with sigmoid activation function with performance superiority of 42.46%, 44.58% and 1.76% using root mean square error, mean absolute error and correlation coefficient performance yardstick, respectively. The developed ELMIA-SINE model further outperforms the existing particle swarm based support vector regression model with polynomial (PSVR-P) and Gaussian (PSVR-G) function with performance improvement of 37.03% and 14.11%, respectively. The dependence of applied magnetic field and dopant concentration on hugeness of magnetocaloric effect was established using the developed model. The precision and the ease of implementation of the developed ELMIA model as compared with the existing models would definitely facilitate exploration of magnetocaloric effect based system of refrigeration for addressing the present energy crisis.

Dielectric phenomena of multiferroic oxides at acoustic- and radio-frequency.

In this review, an overview of acoustic- and radio-frequency frequency dielectric properties of multiferroic oxides, the significant dynamic response of electrical polarization to small external ac electrical fields, are present based on the reports in literatures and our recent experimental progresses. The review is begun with some basic terms, concepts and mechanisms associated with dielectric response and dielectric anomalies, namely dielectric peak and plateau upon varying temperatures and dielectric relaxations upon varying frequencies. Subsequently, a variety of quantitative analyses and descriptions of various dielectric effects, including dielectric relaxation, relaxational and transport dynamics, ac conductivity, equivalent circuit models and impedance spectroscopy, are summarized in details. Next is the kernel section. We thoroughly outline various physical mechanisms behind acoustic-/radio-frequency dielectric responses and anomalies of multiferroic oxides. Spin order transition/spin rotation, charge disorder-order transition, exchange striction of the spin interactions, spin-dependentp-dhybridization mechanism, quantum electric-dipole liquids, the interaction of spin order and quantum paraelectric, the motions of charged defects and carriers, quasi-intrinsic and extrinsic heterogeneous interfaces, polar relaxor and multiglass, ferroic domain wall/boundary motions, etc, are involved in these mechanisms. Meanwhile, particular emphasis is placed on intrinsic or extrinsic magnetodielectric effects and related mechanisms in multiferroic oxides. Finally, the review ends with a short perspective of future dielectric research in multiferroic oxides. This review is able to provide the detailed and unique insights into abundant underlying fundamental physics in multiferroic oxides as well as the potential multiferroics-based technological applications.

Tuning the spin of Dirac fermions on the surface of topological insulators in proximity to a helical spin density wave

We investigate the spin tunability of Dirac fermions on the surface of a 3D topological insulator in proximity to a helical spin density wave, acting as an applied one-dimensional periodic potential for spins produced by spiral multiferroic oxide. It is observed that the spin mean values of Dirac fermion undergo oscillations under the influence of such a periodic potential created by the exchange field of magnetization. The tunability of spin is strongly affected by the strength, orientation and period of the exchange field. In particular, the mean values of spin are anisotropic around the Dirac point, depending strongly on the amplitude and spatial period of the periodic potential. We also find that the spin expectation values change significantly by changing the plane of magnetization. Interestingly, the in-plane components of spin mean values perform pronounced oscillations, whereas the out of plane component does not oscillate at all. The oscillations of planar components of spin are originated from the spin-momentum locking on the surface of topological insulator.

Relativistic ratcheting on the surface of topological insulator Bi2Se3 attached to spiral multiferroic oxide

Relativistic ratcheting of Dirac fermions on the surface of topological insulator Bi2Se3 attached to a spiral multiferroic oxide is investigated. We find that the Dirac fermions on the surface of topological insulator Bi2Se3 exhibit pronounced Brownian motion, tuned by the strength of exchange field established by the interaction of spin degrees of Dirac fermions and multiferroic oxide. The surface Dirac fermions show ratchet effect as a net current under the influence of orthogonal, commensurate ac drives in the presence of a symmetric periodic potential set by the exchange field.

A generalized synthesis method for freestanding multiferroic two-dimensional layered supercell oxide films via a sacrificial buffer layer

A generalized synthesis method for freestanding multiferroic two-dimensional layered supercell oxide films via a sacrificial buffer layer

Heterogeneous Integration of Freestanding Bilayer Oxide Membrane for Multiferroicity.

Transition metal oxides exhibit a plethora of electrical and magnetic properties described by their order parameters. In particular, ferroic orderings offer access to a rich spectrum of fundamental physics phenomena, in addition to a range of technological applications. The heterogeneous integration of ferroelectric and ferromagnetic materials is a fruitful way to design multiferroic oxides. The realization of freestanding heterogeneous membranes of multiferroic oxides is highly desirable. In this study, epitaxial BaTiO3 /La0.7 Sr0.3 MnO3 freestanding bilayer membranes are fabricated using pulsed laser epitaxy. The membrane displays ferroelectricity and ferromagnetism above room temperature accompanying the finite magnetoelectric coupling constant. This study reveals that a freestanding heterostructure can be used to manipulate the structural and emergent properties of the membrane. In the absence of the strain caused by the substrate, the change in orbital occupancy of the magnetic layer leads to the reorientation of the magnetic easy-axis, that is, perpendicular magnetic anisotropy. These results of designing multiferroic oxide membranes open new avenues to integrate such flexible membranes for electronic applications.

Multiferroic properties in Fe-site engineered PbFe1/2Nb1/2O3 with distinct antisymmetric spin interaction

Multiferroic Fe-site engineered lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN] was prepared by partially substituting Fe with Ni, Co, and Cr, which comprise distinct Bohr magnetons, to investigate the effect of the variation in spin configurations on magnetic and multiferroic properties. All the studied compositions exhibited a single-phase perovskite structure, wherein the lattice constant decreased with increasing substitutions. The inherent ferroelectric order was preserved when Ni or Co ions were introduced, while the introduction of Cr made the samples too lossy, which prevented the verification of the possible ferroelectricity. Substitution of Fe with different transition metals in PFN, which is originally paramagnetic at room temperature, resulted in oriented spin configurations that led to distinct magnetic orders: soft ferromagnetic, hard ferromagnetic, and antiferromagnetic orders for Ni, Co, and Cr, respectively. This distinction mainly stems from the interspin distance and the spin moment, both of which are important factors during the spin exchange interaction. The interspin distance of pristine and Cr-substituted PFN is too long and short, respectively, to induce ferromagnetic properties. Moreover, at room temperature, magnetic-field-dependent magnetoelectric coupling was observed only for the Ni- and Co-substituted PFN owing to their asymmetric spin configuration. This research could lead to a general method for modulating the magnetic properties of multiferroic perovskite oxides.

Epitaxial Growth of Aurivillius Bi3Fe2Mn2Ox Supercell Thin Films on Silicon

Nanoelectronic devices integrated with functional complex oxides have drawn much attention in recent years. However, due to material and processing compatibility issues, integrating functional complex oxides with Si-based devices is challenging, and success has been limited. As an example, the Bi3Fe2Mn2Ox (BFMO) supercell system, a single-phase layered oxide made by compositing BiFeO3 and BiMnO3, has been studied for much of the past decade for its unusual layered Aurivillius structure and magnetic and ferroelectric properties. However, most of the BFMO thin film growth has been demonstrated on single-crystal oxide substrates such as SrTiO3 and LaAlO3. In this work, we demonstrate that the BFMO layered supercell phase can be integrated on Si with high epitaxial quality using a buffer stack of TiN/SrTiO3/CeO2. Further understanding of the strain-controlled growth of the BFMO supercell phase has allowed such Si integration. Microstructure, magnetic, ferroelectric, and optical properties of the BFMO films on Si have been characterized and compared with those of BFMO on SrTiO3 single-crystal substrates, demonstrating comparable epitaxial quality and physical properties. Integrating multiferroic BFMO oxides on Si demonstrates the potential of layered supercell oxides in practical device applications such as ferroelectric field effect transistors.

Electric field control of magnetic states in ferromagnetic-multiferroic nanostructures.

Multiferroic oxides are considered as key elements of energy-consuming devices required for the development of scalable logic and information storage technologies. In this regard, understanding the mechanisms of magnetoelectric switching and finding the optimal way to switch magnetization by an electric field is of crucial importance. In this study, we develop a model for studying magnetic states in a nanoscale exchange-coupled ferromagnetic-multiferroic heterostructure subjected to the action of an electric field. Based on bias effects emerging due to the coupling between a ferromagnetic subsystem and an antiferromagnetically ordered multiferroic material, we explore the magnetic textures and the magnetization reversal processes in a ferromagnet. As the multiferroic material, we consider BiFeO3, where magnetic ordering and ferroelectric ordering are determined by the mutually perpendicular antiferromagnetic (L), weak ferromagnetic (M) and polarization (P) vectors. Application of an electric voltage removes degeneration from eight energetically equivalent positions of P|| 〈111〉, allocates the definite directions of vectors P, M, and L and as a consequence the unidirectional magnetic anisotropy axis in the reference ferromagnetic layer. Our study reveals the features of the magnetic configurations in systems of different geometries, with varying exchange and magnetic anisotropy, necessary to determine the optimal conditions for switching magnetic states in a multiferroic bi-layer by an electric field.

Effects of Multiple Local Environments on Electron Energy Loss Spectra of Epitaxial Perovskite Interfaces.

The role of local chemical environments in the electron energy loss spectra of complex multiferroic oxides was studied using computational and experimental techniques. The evolution of the O K-edge across an interface between bismuth ferrite (BFO) and lanthanum strontium manganate (LSMO) was considered through spectral averaging over crystallographically equivalent positions to capture the periodicity of the local O environments. Computational techniques were used to investigate the contribution of individual atomic environments to the overall spectrum, and the role of doping and strain was considered. Chemical variation, even at the low level, was found to have a major impact on the spectral features, whereas strain only induced a small chemical shift to the edge onset energy. Through a combination of these methods, it was possible to explain experimentally observed effects such as spectral flattening near the interface as the combination of spectral responses from multiple local atomic environments.

Visualizing Giant Ferroelectric Gating Effects in Large-Scale WSe2/BiFeO3 Heterostructures.

Multilayers based on quantum materials (complex oxides, topological insulators, transition-metal dichalcogenides, etc.) have enabled the design of devices that could revolutionize microelectronics and optoelectronics. However, heterostructures incorporating quantum materials from different families remain scarce, while they would immensely broaden the range of possible applications. Here we demonstrate the large-scale integration of compounds from two highly multifunctional families: perovskite oxides and transition-metal dichalcogenides (TMDs). We couple BiFeO3, a room-temperature multiferroic oxide, and WSe2, a semiconducting two-dimensional material with potential for photovoltaics and photonics. WSe2 is grown by molecular beam epitaxy and transferred on a centimeter-scale onto BiFeO3 films. Using angle-resolved photoemission spectroscopy, we visualize the electronic structure of 1 to 3 monolayers of WSe2 and evidence a giant energy shift as large as 0.75 eV induced by the ferroelectric polarization direction in the underlying BiFeO3. Such a strong shift opens new perspectives in the efficient manipulation of TMD properties by proximity effects.

Oxide magnonics: Spin waves in functional magnetic oxides

Spin waves or their quanta magnons are collective excitations in magnetically ordered materials. Magnonics have recently attracted tremendous interest for building next-generation nanoscale devices and circuits with low-power consumption. Oxide materials provide an excellent platform for achieving highly efficient spin-wave excitation and transmission for magnonic applications with versatile functionalities. In this article, we review some recent advances for oxide-based magnonics, including both magnetic oxides for hosting spin waves and non-magnetic oxides for manipulating spin waves. First, we introduce recent development on coherent propagation and incoherent transport of magnons in thin-film iron garnets, low-damping ferrimagnetic oxides widely used in magnonics. Then, we discuss spin-wave chirality due to the inversion symmetry broken in magnetic oxides. Magnonics in antiferromagnetic oxides is also presented, where the spin-wave resonance frequency enters THz regime. Nanoscale spin textures, such as magnetic skyrmions, can be stabilized in magnetic oxides, and provide additional versatilities by coupling their dynamics with spin waves. Last but not the least, we highlight the electrical control of spin waves based on multiferroic oxides toward applications for hybrid magnonics.