Ferroic Properties Research Articles

Controlling the dielectric constant values of nematic liquid crystals using ferroelectric and multiferroic nanoparticles

Notably, the simultaneous manifestation of ferromagnetic and ferroelectric properties at ambient temperature has spurred significant interest in incorporating multiferroic bismuth ferrite nanoparticles (BiFeO3) into liquid crystal matrices. In this study, the parallel and perpendicular dielectric components ( and ) and dielectric anisotropy () of two different nanoparticles, barium titanate (BaTiO3) and BiFeO3, doped into E7, were measured at various temperatures and frequencies. Nematic mixture E7, a widely utilized nematic liquid crystal in research and display technologies, is a eutectic mixture composed of four cyanobiphenyl derivatives i.e. 5CB, 7CB, 8OCB, and 5CT. The findings indicate a substantial reduction in dielectric anisotropy upon introducing nanoparticles into the nematic liquid crystal environment. This research highlights the significant influence of barium titanate nanoparticles, which are smaller (approximately 12 nm), on the dielectric constant. This effect was analyzed based on varying concentrations and compared to a nanoparticle with ferroic properties. Moreover, the dielectric constant can be modulated through an alternative approach. Specifically, applying an electric field during the filling process of liquid crystal cells leads to changes in the dielectric constant. These changes, observed for both nanoparticles, were particularly evident at a precise concentration of 0.1 wt%, resulting in a decreased dielectric constant.

Interfacial strain induced giant magnetoresistance and magnetodielectric effects in multiferroic BCZT/LSMO thin film heterostructures

Layered thin films of the ferroelectric perovskite Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) and the ferromagnetic half-metal La0.80Sr0.20MnO3 (LSMO) are well-known multiferroic systems that show promise for spintronic applications. In this work, the structure–property relationships are explored in novel BCZT/LSMO thin film heterostructures with optimized ferroic properties. Epitaxial BCZT/LSMO thin film heterostructures are grown by varying the lattice mismatch strains on single crystal LaAlO3 (LAO) (100) and MgO (100) substrates using the pulsed laser deposition technique. The epitaxial strain in the films gives rise to a tetragonal distortion of the BCZT and LSMO unit cells and significantly affects their magnetotransport and magnetodielectric properties. The BCZT/LSMO/LAO heterostructure exhibits a colossal magnetoresistance effect due to a large out-of-plane tensile strain, which induces enhanced carrier hopping in the LSMO layer as compared to the BCZT/LSMO/MgO film. The larger tetragonal distortion of the BCZT unit cell in BCZT/LSMO/MgO contributes to higher dielectric permittivity, with a greater dielectric maxima temperature and freezing temperature. Magnetodielectric measurements reveal a hitherto unobserved giant magnetodielectric effect in the BCZT/LSMO/MgO film, attributed to a large in-plane strain, which induces interfacial polarization distortion at the interfacial layer. Overall, this work elucidates the unique strain and charge-mediated cross-coupled phenomena of magnetic and electric orders in multiferroic thin film heterostructures, which are critical for their technological applications.

Observation of stabilized negative capacitance effect in hafnium-based ferroic films

A negative capacitance (NC) effect has been proposed as a critical pathway to overcome the ‘Boltzmann tyranny’ of electrons, achieve the steep slope operation of transistors and reduce the power dissipation of current semiconductor devices. In particular, the ferroic property in hafnium-based films with fluorite structure provides an opportunity for the application of the NC effect in electronic devices. However, to date, only a transient NC effect has been confirmed in hafnium-based ferroic materials, which is usually accompanied by hysteresis and is detrimental to low-power transistor operations. The stabilized NC effect enables hysteresis-free and low-power transistors but is difficult to observe and demonstrate in hafnium-based films. This difficulty is closely related to the polycrystalline and multi-phase structure of hafnium-based films fabricated by atomic layer deposition or chemical solution deposition. Here, we prepare epitaxial ferroelectric Hf0.5Zr0.5O2 and antiferroelectric ZrO2 films with single-phase structure and observe the capacitance enhancement effect of Hf0.5Zr0.5O2/Al2O3 and ZrO2/Al2O3 capacitors compared to that of the isolated Al2O3 capacitor, verifying the stabilized NC effect. The capacitance of Hf0.5Zr0.5O2 and ZrO2 is evaluated as −17.41 and −27.64 pF, respectively. The observation of the stabilized NC effect in hafnium-based films sheds light on NC studies and paves the way for low-power transistors.

Engineering polar distortions in multiferroic Sr1−xBaxMnO3−δ thin films

The physical properties of perovskite oxide thin films are governed by the subtle interplay between chemical composition and crystal symmetry variations, which can be altered by epitaxial growth. In the case of perovskite-type multiferroic thin films, precise control of stoichiometry and epitaxial strain allows for gaining control over the ferroic properties through selective crystal distortions. Here, we demonstrate the chemical tailoring of the polar atomic displacements by tuning the stoichiometry of multiferroic Sr1−xBaxMnO3−δ (0 ≤ x ≤ 0.5) epitaxial thin films. A combination of x-ray diffraction and aberration-corrected scanning transmission electron microscopy enables unraveling the local polarization orientation at the nanoscale as a function of the film’s composition and induced crystalline structure. We demonstrate experimentally that the orientation of polarization is intimately linked to the Ba doping and O stoichiometry of the films and, with the biaxial strain induced by the substrate, it can be tuned either in-plane or out-of-plane with respect to the substrate by the appropriate choice of the post-growth annealing temperature and O2 atmosphere. This chemistry-mediated engineering of the polarization orientation of oxide thin films opens new venues for the design of functional multiferroic architectures and the exploration of novel physics and applications of ferroelectric textures with exotic topological properties.

Structural analysis, ferroic properties with enhanced magnetoelectric coupling in novel (1-x)BiFeO3-(x)GdFeO3 nanocomposites

Multiferroic composites exhibit substantially greater magnetoelectric interaction among order variables as compared to single-phase multiferroics, making them particularly attractive for futuristic multi-state RAM and spintronic gadgets. The multiferroic nanocomposites (1-x)BiFeO3-xGdFeO3 (x = 0.05, 0.10, 0.15, & 0.20) are synthesized by using solid-state route. The crystallographic and profile parameters are extracted from the dual-phase refinement of the rhombohedral (R3c) and orthorhombic (Pbnm) crystal structures. The optimized density, crystallite size and homogenous microstructure may be responsible for the improved dielectric and ferroic properties. TEM images reveal a reduction in the particle size (67–59 nm) upon GdFeO3 (GFO) loading. The HRTEM images unravel the interplanar spacing and associated Bragg planes, while the SAED rings validate the polycrystalline features of the samples. The high Curie temperature (Tc ̴ 643 °C) with enhanced specific heat (Cp ̴ 29.5 J/g°C) in x= 0.10 sample ensures its stable operation, efficient heat dissipation, minimal overheating, and greater thermal stability for reliable performance in demanding conditions. The surface and finite-size effects enhanced the magnetization (MS=1.04emu/g) in nanostructured ferromagnetic nanocomposite, making it a promising candidate for high-density magnetic storage devices and sensors. The high polarization (Pmax=8.39µC/cm2) and ME-coupling coefficient (αE=0.16mVcm−1Oe−1) observed in the most dense nanocomposite make it a potential candidate for magnetoelectric applications.

In-Plane Ferrielectric Order in van der Waals β'-In2Se3.

van der Waals ferroic materials exhibit rich potential for implementing future generation functional devices. Among these, layered β'-In2Se3 has fascinated researchers with its complex superlattice and domain structures. As opposed to ferroelectric α-In2Se3, the understanding of β'-In2Se3 ferroic properties remains unclear because ferroelectric, antiferroelectric, and ferroelastic characteristics have been separately reported in this material. To develop useful applications, it is necessary to understand the microscopic structural properties and their correlation with macroscopic device characteristics. Herein, using scanning transmission electron microscopy (STEM), we observed that the arrangement of dipoles deviates from the ideal double antiparallel antiferroelectric character due to competition between antiferroelectric and ferroelectric structural ordering. By virtue of second-harmonic generation, four-dimensional STEM, and in-plane piezoresponse force microscopy, the long-range inversion-breaking symmetry, uncompensated local polarization, and net polarization domains are unambiguously verified, revealing β'-In2Se3 as an in-plane ferrielectric layered material. Additionally, our device study reveals analogous resistive switching behaviors of different types owing to polarization switching, defect migration, and defect-induced charge trapping/detrapping processes.

Ferroic Phases in Two-Dimensional Materials.

Two-dimensional (2D) ferroics, namely ferroelectric, ferromagnetic, and ferroelastic materials, are attracting rising interest due to their fascinating physical properties and promising functional applications. A variety of 2D ferroic phases, as well as 2D multiferroics and the novel 2D ferrovalleytronics/ferrotoroidics, have been recently predicted by theory, even down to the single atomic layers. Meanwhile, some of them have already been experimentally verified. In addition to the intrinsic 2D ferroics, appropriate stacking, doping, and defects can also artificially regulate the ferroic phases of 2D materials. Correspondingly, ferroic ordering in 2D materials exhibits enormous potential for future high density memory devices, energy conversion devices, and sensing devices, among other applications. In this paper, the recent research progresses on 2D ferroic phases are comprehensively reviewed, with emphasis on chemistry and structural origin of the ferroic properties. In addition, the promising applications of the 2D ferroics for information storage, optoelectronics, and sensing are also briefly discussed. Finally, we envisioned a few possible pathways for the future 2D ferroics research and development. This comprehensive overview on the 2D ferroic phases can provide an atlas for this field and facilitate further exploration of the intriguing new materials and physical phenomena, which will generate tremendous impact on future functional materials and devices.

K.A. Müller and research on ferroic and polaronic materials

K.A. Müller mentored work outside IBM on Ferroic and Polaronic Materials already in the 1970s and showed a keen interest in any progress made in these fields afterwards. He supported particularly research of the ferroelastic materials SrTiO3 and LaAlO3. He was also fascinated by research into polaronic states of WO3 and their effect on ferroic properties in perovskite samples. This demonstrates that his activities were not restricted to superconductivity but extended more generally in solid-state sciences including the field of phase transitions and pattern formations in nanomaterials.

Structural evolution and coexistence of ferroelectricity and antiferromagnetism in Fe, Nb co-doped BaTiO3 ceramics

Multiferroics are materials that exhibit two or more primary ferroic properties within the same phase and have potential applications in sensors, spintronics and memory devices. Here, the dielectric, ferroelectric and magnetic properties of novel multiferroics derived from BaTi1−x(Fe0.5Nb0.5)xO3 (BTFN, 0.01 ≤ x ≤ 0.10) ceramics are investigated. Multiferroism in these ceramics is manifested by the coexistence of ferroelectric long-range ordering and antiferromagnetism. With increasing x-value, there is a structural evolution from a tetragonal perovskite to a mixture of tetragonal and cubic phases, accompanied by a decrease in the temperature of maximum permittivity. At room temperature, ferroelectric behaviour is evidenced by the presence of current peaks corresponding to domain switching in the current-electric field loops, while the observation of non-linear narrow magnetic hysteresis loops suggests dilute magnetism. The results indicate that in the x = 0.07 composition the antiferromagnetic order is established through an indirect super-exchange interaction between adjacent Fe ions.

Wavelength dependence of polarization-resolved second harmonic generation from ferroelectric SnS few layers

Two-dimensional group-IV monochalcogenides such as GeS, GeSe, SnS, and SnSe were theoretically predicted as multiferroic materials with two or more ferroic properties. However, most of their bulk crystals are stacked layer by layer with an antiferroelectric manner, which lose the macroscopic in-plane ferroelectricity. In this work, we studied SnS in which the layers are stacked in a ferroelectric manner both experimentally and theoretically. We utilized polarization-resolved second harmonic generation (SHG) microscopy to investigate numerous flakes of ferroelectric SnS few layers on mica substrates. We found the SHG polar patterns dramatically varied in the range of 800 nm and 1000 nm due to the frequency-dependent SHG susceptibilities. First-principles calculations have been performed to study the frequency-dependent and layer-dependent SHG susceptibilities in the ferroelectric SnS with AA and AC stacking orders. The variation trend of calculated SHG polar patterns as a function of frequency agrees well with that of the experimental results. Since polarization-resolved SHG is a noncontact and nondestructive technique to determine the crystal orientation, understanding of its properties is important, especially for monitoring the transition of different ferroic phases.

Epitaxial growth of hexagonal GdFeO3 thin films with magnetic order by pulsed laser deposition

• Hexagonal GdFeO 3 films were prepared using pulsed laser deposition. • The films were obtained on indium tin oxide (ITO(111)) layer. • The hexagonal GdFeO 3 film showed weak ferromagnetism. Hexagonal rare-earth iron oxides, h - R FeO 3 , are promising multiferroic materials. The ferroic properties of h - R FeO 3 can be controlled by varying R . However, h - R FeO 3 exists in a metastable phase, resulting in a limit of available range of R . In this study, we fabricated h -GdFeO 3 phase via epitaxial stabilization. The h -GdFeO 3 epitaxial film with c -axis orientation was deposited on an indium tin oxide (ITO(111)) layer as the bottom electrode via pulsed laser deposition. The metastable hexagonal phase was obtained in a narrow range of deposition parameters. High-crystalline h -GdFeO 3 film was obtained at substrate temperature of 780 °C and oxygen pressure of 13 Pa. The a -axis of the h -GdFeO 3 phase is parallel to the [11–2] directions of ITO(111) layer. The h -GdFeO 3 film exhibited weak ferromagnetism with a Néel temperature of 43 K, which was lower than that of the previously reported h - R FeO 3 films ( R = Dy–Lu, Y and Sc) owing to the longer a -axis.

Enantiomeric Hydrogen-bonded Chains Driving Ferroelectric and Nonlinear Optical Behavior

Organic multiferroic materials have been widely investigated due to their novel physical properties and broad applications. However, the discovery of organic small-molecular multiferroic compounds is still rare. Herein, based on the chemical design strategy of introducing homochirality, we present a pair of enantiomeric organic small-molecular compounds [HDABCO (1,4-diazabicyclo[2.2.2]octonium)][l- and d-MA (malic acid)], which displays high Curie temperatures (Tc) of 409/412 K, superior optoelectronic performance, and unique ferroelectric and ferroelastic nature. In comparison with the reported ferroelectrics with the [HDABCO]+ cation chain structure, the enantiomers show a neutral one-dimensional chain, where hydrogen bonds connect [HDABCO]+ cations and [MA]− anions. Strikingly, [HDABCO][l- and d-MA] exhibit a large second harmonic generation (SHG) intensity of about 2.46 and 2.53 times that of KH2PO4 (KDP), exceeding those of all the organic ferroelectrics (about 0.2–1 × KDP). With excellent SHG signal and ferroic properties, as well as the merit of low acoustic impedance z0 matching that of the body and easy processing, [HDABCO][l- and d-MA] are potential candidates for future biocompatible electronic devices with multi-functionality.

Weak ferromagnetism in Tb(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)O3 high-entropy oxide perovskite thin films

High-entropy oxide thin films have recently been introduced as an attractive strategy to design and enhance ferroic properties. Here, the authors perform element-sensitive x-ray absorption spectroscopy and magnetometry on high-entropy oxide perovskite thin films, shedding light on how different transition metal elements contribute to the overall magnetic response. The results demonstrate not only how disorder can lead to enhancement of magnetic properties but also provide a route towards further improvements of other desired properties in corresponding oxide thin films.

First-principles indicators of ferroic parameters in epitaxial BiFeO3 and BiCrO3

Density-functional theory is used to validate spin-resolved and orbital-resolved metrics of localized electronic states to anticipate ferroic and dielectric properties of BiFeO3 and BiCrO3 under epitaxial strain. Using previous investigations of epitaxial phase stability in these systems, trends in properties such as spontaneous polarization and bandgap are compared to trends in atomic orbital occupation derived from projected density of states. Based on first principles theories of ferroic and dielectric properties, such as the Modern Theory of Polarization for spontaneous polarization or Goodenough–Kanamori theory for magnetic interactions, this work validates the sufficiency of metrics of localized electronic states to predict trends in multiple ferroic and dielectric properties. Capabilities of these metrics include the anticipation of the transition from G-Type to C-Type antiferromagnetism in BiFeO3 under 4.2% compressive epitaxial strain and the interval of C-Type antiferromagnetism from 3% to 7% tensile epitaxial strain in BiCrO3. The results of this work suggest a capability of localized electronic metrics to predict multiferroic characteristics in the BiXO3 systems under epitaxial strain, with single or mixed B-site occupation.

Intercalation-driven ferroelectric-to-ferroelastic conversion in a layered hybrid perovskite crystal

Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted intense interests due to their quantum well structure and tunable excitonic properties. As an alternative to the well-studied divalent metal hybrid perovskite based on Pb2+, Sn2+ and Cu2+, the trivalent metal-based (eg. Sb3+ with ns2 outer-shell electronic configuration) hybrid perovskite with the A3M2X9 formula (A = monovalent cations, M = trivalent metal, X = halide) offer intriguing possibilities for engineering ferroic properties. Here, we synthesized 2D ferroelectric hybrid perovskite (TMA)3Sb2Cl9 with measurable in-plane and out-of-plane polarization. Interestingly, (TMA)3Sb2Cl9 can be intercalated with FeCl4 ions to form a ferroelastic and piezoelectric single crystal, (TMA)4-Fe(iii)Cl4-Sb2Cl9. Density functional theory calculations were carried out to investigate the unusual mechanism of ferroelectric-ferroelastic crossover in these crystals.

Inside Cover Picture

Intermolecular interaction is crucial to the study of molecular dynamics. Hydrogen bond, as a special molecular interaction, has been proved an important weak interaction to influence the motions of molecular in an organic system, and it could optimize or may produce ferroelectric, ferroelastic, and ferromagnetic features. However, research on the above properties realized by hydrogen‐bond engineering is relatively rare in hybrid compounds. Therefore, we want to explore whether the enhancement of ferroic properties could be achieved through the construction of hydrogen bonds in molecular hybrid systems. Here, a ferroelastic phase transition temperature range of hybrid perovskite (Me‐Hdabco)Rb[BF4]3 is significantly increased by 71 K compared with that of [Medabco‐F]Rb[BF4]3 by constructing hydrogen bonds. This work provides the way for designing functional molecular hybrid crystals. More details are given in the article by Fu et al. on page 1559—1565.image

Enhancement of room-temperature magnetization in GaFeO3-type single crystals by Al and Sc doping

GaFeO3-type oxides are promising multiferroic materials due to the coexistence of spontaneous magnetization and ferroelectric polarization properties at room temperature. As these ferroic properties feature a large anisotropy, single crystals are required. However, the magnetization of GaFeO3-type single crystals remains low at room temperature. In this study, we largely enhanced the magnetization at room temperature of GaFeO3-type single crystals by increasing the Fe content and co-doping Sc3+ and Al3+. Single crystals of AlxSc0.1−xGa0.6Fe1.3O3 (x = 0.01–0.04) were prepared using the optical floating-zone method. The single crystals were rod-shaped, with a diameter and length of ∼6 mm and 7 cm, respectively. X-ray diffraction measurements confirmed the ferroelectric polarization of the crystals. In addition, they exhibited room-temperature ferrimagnetism, with Curie temperature in the range of 326–338 K; the crystals exhibit magnetic anisotropy along the a-axis. The magnetization of the single crystal at 300 K and 0.3 kOe was 13 emu g−1, which is over ten times larger than those of previously reported single crystals with GaFeO3-type crystal structure.

The Bright and Dark Shades of Transparent Conducting Perovskites: From Science to Global Market

From band theory of solids, it is well known that electrical conductivity and optical transparency are mutually exclusive properties. However, due to advancement in science and technology, controlled doping has allowed to merge these properties in few materials such as thin films, bulk oxides, conducting polymers and carbon-based materials and are collectively known as transparent conducting oxides (TCO) and transparent conducting films (TCF). Recently, this extraordinary property is also found in doped nano-perovskites and hence can further meets the diversified demand in the field of photovoltaics, LCDs, FETs, diodes, supercapacitors and many more. For such applications, doped perovskite TCOs have becomes highly important and cost effective for the future global markets. This paper will summarize the status and progress of various TCOs which are particularly perovskite in structure. Future direction and challenges of doped Perovskites in the techno-era are also discussed. Several examples of TCO-Perovskites are presented with a discussion of their ferroic, magnetic, electrical and optical properties. On addition, the concerns related to thermal and chemical stability of TCO-Doped Perovskites are vividly reviewed.

Magnetoelectric coupling susceptibility in novel lead-free 0–3 type multiferroic particulate composites of (1-x)Na0.5Bi0.5TiO3 -(x)CoCr0.4Fe1.6O4

Lead-free 0–3 particulate composites of chromium substituted cobalt nano-ferrite CoCr0.4Fe1.6O4 (CCFO) and sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) having molar ratio of (1-x)Na0.5Bi0.5TiO3 -(x)CoCr0.4Fe1.6O4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5& 1) have been investigated. XRD patterns reveal that the composites crystallized with binary rhombohedraland cubic phase, equivalent to room temperature crystal symmetry of host ferroelectric NBT and magnetic CCFO materials, respectively. SEM micrographs depict the presence of both parent phases with different micro-structural symmetries. The observed ferroic properties, derived from isothermal magnetization and polarization measurements, emphasize that all the (1-x)NBT - (x)CCFO compositions exhibit significant sensitivity towards the magnetic field as well as the electric field. To evaluate the degree of magnetoelectric coupling in CCFO-NBT composites, we employed the magneto-dielectric characterization technique as a sensitive probing tool. We note that magneto-dielectric property initially increases with x and is found to be maximum ∼ −0.78% (x = 0.4) and further decreases with x. This unconventional product behaviour of particulate composite system is availed through magnetostrictive nature of magnetic subsystem - CFO and piezoelectric characteristics of ferroelectric- NBT. These lead-free multiferroic composites may provide an opportunity for the miniaturization of environmental-friendly magnetoelectric (ME) devices.

Two-Dimensional Organoferroelasticity in a Single Crystal of 4-Iodoaniline

A ferroic property such as ferroelasticity in an organic molecular crystal is a lucrative and crucial area to explore and investigate, owing to its potentiality in developing mechanical materials. Direction-dependent mechanical deformations are probable in organic compounds; however, isotropic deformation seems improbable due to their anisotropic structural nature. In this work, we report two-dimensional ferroelasticity in 4-iodoaniline undergoing deformation on two mutually orthogonal planes on the application of external stress, which was investigated by force measurement and single-crystal X-ray diffraction techniques at macroscopic and microscopic levels.