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This is an update of a previous review (Naumis et al 2017 Rep. Prog. Phys. 80 096501). Experimental and theoretical advances for straining graphene and other metallic, insulating, ferroelectric, ferroelastic, ferromagnetic and multiferroic 2D materials were considered. We surveyed (i) methods to induce valley and sublattice polarisation (P) in graphene, (ii) time-dependent strain and its impact on graphene's electronic properties, (iii) the role of local and global strain on superconductivity and other highly correlated and/or topological phases of graphene, (iv) inducing polarisation P on hexagonal boron nitride monolayers via strain, (v) modifying the optoelectronic properties of transition metal dichalcogenide monolayers through strain, (vi) ferroic 2D materials with intrinsic elastic (σ), electric (P) and magnetic (M) polarisation under strain, as well as incipient 2D multiferroics and (vii) moiré bilayers exhibiting flat electronic bands and exotic quantum phase diagrams, and other bilayer or few-layer systems exhibiting ferroic orders tunable by rotations and shear strain. The update features the experimental realisations of a tunable two-dimensional Quantum Spin Hall effect in germanene, of elemental 2D ferroelectric bismuth, and 2D multiferroic NiI2. The document was structured for a discussion of effects taking place in monolayers first, followed by discussions concerning bilayers and few-layers, and it represents an up-to-date overview of exciting and newest developments on the fast-paced field of 2D materials. [ABSTRACT FROM AUTHOR]

Solid state compounds exhibiting multiple and coupled macroscopic orders, named multiferroics, represent a challenge for both theoretical and experimental modern condensed-matter physics. Spins and the electric polarisation in conventional magnetic and ferroelectric materials can be manipulated on their fundamental timescales, by means of femtosecond laser pulses. In view of the resounding success and popularity of the all-optical approach, it is only natural to wonder about the application of this scheme to study the intrinsic coupling between spins and charges in multiferroics. Deeply fundamental questions arise: can ultrashort laser pulses deterministically activate, enhance or suppress the magnetoelectric coupling on the femtosecond timescale? Can these processes be triggered in a fully coherent fashion, thus being unrestrained by any thermal load? Which mechanism of spin-charge coupling is most favourable to overcome these overarching and daunting challenges? This problem is interdisciplinary in nature, requiring contributions from materials science and condensed matter physics from both theoretical and experimental perspectives. High-quality materials suitable for optical investigations have to be identified, synthetized and characterised. General and valid models offer then a guide to the plethora of possible light-induced processes, resulting in the desired ultrafast multiferroic manipulations. Finally, healthy experimental schemes, able to unambiguously track the ultrafast dynamics of either the ferroelectric or the magnetic order parameter have to be developed and implemented. Our motivation to write this review is to lay a broad and multidisciplinary foundation, which may be employed as a starting point for non-equilibrium approaches to the manipulation of the multiferroicity on the femtosecond timescale. This was also one of the main goals of the COST Action MAGNETOFON, whose network constitutes the core of the authors of this review. The present work thus represents a part of the scientific legacy of MAGNETOFON itself. [ABSTRACT FROM AUTHOR]

Multiferroic materials have generated great interest due to their potential as functional device materials. Nanocomposites have been increasingly used to design and generate new functionalities by pairing dissimilar ferroic materials, though the combination often introduces new complexity and challenges unforeseeable in single-phase counterparts. The recently developed approaches to fabricate 3D super-nanocomposites (3D‐sNC) open new avenues to control and enhance functional properties. In this work, we develop a new 3D‐sNC with CoFe2O4 (CFO) short nanopillar arrays embedded in BaTiO3 (BTO) film matrix via microstructure engineering by alternatively depositing BTO:CFO vertically-aligned nanocomposite layers and single-phase BTO layers. This microstructure engineering method allows encapsulating the relative conducting CFO phase by the insulating BTO phase, which suppress the leakage current and enhance the polarization. Our results demonstrate that microstructure engineering in 3D‐sNC offers a new bottomâ€"up method of fabricating advanced nanostructures with a wide range of possible configurations for applications where the functional properties need to be systematically modified. [ABSTRACT FROM AUTHOR]

Interactions of terahertz radiations with matter can lead to the realization of functional devices related to sensing, high-speed communications, non-destructive testing, spectroscopy, etc In spite of the versatile applications that THz can offer, progress in this field is still suffering due to the dearth of suitable responsive materials. In this context, we have experimentally investigated emerging multiferroic BiFeO3 film (∼200 nm) employing terahertz time-domain spectroscopy (THz-TDS) under vertically applied (THz propagation in the same direction) electric fields. Our experiments reveal dynamic modulation of THz amplitude (up to about 7% within 0.2â€"1 THz frequency range) because of the variation in electric field from 0 to 600 kV cmâˆ'1. Further, we have captured signatures of the hysteretic nature of polarization switching in BiFeO3 film through non-contact THz-TDS technique, similar trends are observed in switching spectroscopy piezoresponse force microscope measurements. We postulate the modulation of THz transmissions to the alignment/switching of ferroelectric polarization domains (under applied electric fields) leading to the reduced THz scattering losses (hence, reduced refractive index) experienced in the BiFeO3 film. This work indicates ample opportunities in integrating nanoscale multiferroic material systems with THz photonics in order to incorporate dynamic functionalities to realize futuristic THz devices. [ABSTRACT FROM AUTHOR]

Ferroelectric and magnetic properties are investigated for Bi2Fe4O9 nanoparticles with different shapes (cuboid and sphere-like) synthesized by hydrothermal and sol-gel method. The magnetic study reveals that coercivity, Neel temperature and remanent magnetization strongly depend on shape of the particle. The nanoparticle with sphere-like shape exhibits magnetization curve of antiferromagnetic (AFM) ordering with ferromagnetic (FM) component. As the particle shape changes from sphere-like to cuboid, the AFM component is dominating over the ferromagnetic component. A small exchange bias is also observed at low temperature in both the sphere-like and cuboid nanoparticle. The coercivity, remanent magnetization and Neel temperature of sphere-like nanoparticle is greater than cuboid nanoparticle. Ferroelectric measurement shows the remanent polarization of cuboid is greater than sphere-like nanoparticle but the coercivity is almost same. This Bi2Fe4O9 nanoparticle shows a small change in polarization under magnetic field. The polarization value decreases with magnetic field increases. The magnetoelectric coupling-measured by change of remanent polarization under magnetic field are found to be greater in Bi2Fe4O9 sphere-like nanoparticles. These shape dependent magnetic and ferroelectric properties are coming because of shape anisotropy. [ABSTRACT FROM AUTHOR]

Its an absolute pleasure to be able to write this article to honor Professor John Goodenough on his 100th birthday. John, here is wishing you many more years of wonderful science with mirth and laughter! I have had the pleasure of knowing John for more than two decades and also following in his footsteps (albeit at a great distance from him), working on complex correlated oxides for my entire professional career, starting from the Hi-TC cuprates, manganites that display colossal magnetoresistance, ferroelectricity and most recently looking at the coupling between electricity and magnetism in multiferroics as well as the intricacies of spin transport in correlated oxides. This article is written on behalf of many colleagues, collaborators, and researchers in the field of complex oxides as well as current and former students and postdocs who continue to enable and undertake cutting-edge research in the field of multiferroics, magnetoelectrics, and broadly correlated electron materials physics as well as the pursuit of electric-field control of magnetism. What I present is something that is extremely exciting from both a fundamental science and applications perspective and has the potential to revolutionize the field of microelectronics. To realize this potential will require numerous new innovations, both in the fundamental science arena as well as translating these scientific discoveries into real applications. Thus, this article attempts to bridge the gap between fundamental materials physics and the actual manifestations of the physical concepts into real-life applications, a spirit that John’s entire career has embraced. [ABSTRACT FROM AUTHOR]

The primary order parameter of hybrid improper ferroelectricity (HIF) is not spontaneous polarisation but nonpolar modes such as oxygen octahedral rotations (OORs), antipolar, or even Jahnâ€"Teller distortions; therefore, the HIF mechanism may be applied as an effective pathway to tune electronic bandgaps, control orbitals, and create multiferroicity. Most of the current experimental research on HIF is focused on layered perovskite oxides; therefore, this review focuses on the recent progress of experimental studies on HIF materials with the Ruddlesdenâ€"Popper (Râ€"P) and Dionâ€"Jacobson (Dâ€"J) structures. Experimental research on double-layered Râ€"P oxides is included, and the linear relationship between the Curie temperature and tolerance factor has been established. Moreover, the coexistence of polar and weak ferromagnetic phases has been observed in iron-based double-layered Râ€"P oxides at room temperature. The recent discovery of ferroelectricity in A-site cation-ordered triple-layered Râ€"P oxides has significantly expanded the HIF field. HIF has also been confirmed in caesium- and rubidium-based double-layered Dâ€"J oxides, and complex OOR modes have been observed in Dâ€"J oxides. Although significant progress has been achieved for HIF materials in layered perovskite oxides, extensive research is required to reveal the mysteries of HIF and to create single-phase multiferroics in HIF materials. [ABSTRACT FROM AUTHOR]

An effective regulation of the magnetism and interface of ferromagnetic materials is not only of great scientific significance, but also has an urgent need in modern industry. In this work, by using the first-principles calculations, we demonstrate an effective approach to achieve non-volatile electrical control of ferromagnets, which proves this idea in multiferroic heterostructures of ferromagnetic LaTiO3 and ferroelectric BiFeO3. The results show that the magnetic properties and two-dimensional electron gas concentrations of LaTiO3 films can be controlled by changing the polarization directions of BiFeO3. The destroyed symmetry being introduced by ferroelectric polarization of the system leads to the transfer and reconstruction of the Ti-3d electrons, which is the fundamental reason for the changing of magnetic properties. This multiferroic heterostructures will pave the way for non-volatile electrical control of ferromagnets and have potential applications. [ABSTRACT FROM AUTHOR]

The coupling between electric ordering and magnetic ordering in two-dimensional (2D) materials is important for both fundamental research of 2D multiferroics and future development of magnetism-based information storage and operation. Here, we introduce a scheme for realizing a magnetic phase transition through the transition of electric ordering. We take CuMoP2S6 monolayer as an example, which is a member of the large 2D transition-metal chalcogen-phosphates family. Based on first-principles calculations, we find that it is a multiferroic with unprecedented characters, namely, it exhibits two different phases: an antiferroelectric-antiferromagnetic phase and a ferroelectric-ferromagnetic phase, in which the electric and magnetic orderings are strongly coupled. Importantly, the electric polarization is out-of-plane, so the magnetism can be readily switched by using the gate electric field. Our finding reveals a series of 2D multiferroics with special magnetoelectric coupling, which hold great promise for experimental realization and practical applications. [ABSTRACT FROM AUTHOR]

A chiral absorber of light can emit spin-polarized (circularly polarized) thermal radiation based on Kirchhoff's law which equates spin-resolved emissivity with spin-resolved absorptivity for reciprocal media at thermal equilibrium. No such law is known for nonreciprocal media. In this work, we discover three spin-resolved Kirchhoff's laws of thermal radiation applicable for both reciprocal and nonreciprocal planar media. In particular, these laws are applicable to multi-layered or composite slabs of generic bianisotropic material classes which include (uniaxial or biaxial) birefringent crystals, (gyrotropic) Weyl semimetals, magnetized semiconductors, plasmas, ferromagnets and ferrites, (magnetoelectric) topological insulators, metamaterials and multiferroic media. We also propose an experiment to verify these laws using a single system of doped indium antimonide (InSb) thin film in an external magnetic field. Furthermore, we reveal a surprising result that the planar slabs of all these material classes can emit partially circularly polarized thermal light without requiring any surface patterning, and identify planar configurations which can experience nontrivial thermal optomechanical forces and torques upon thermal emission into the external environment at lower temperature (nonequilibrium). Our work also provides a new fundamental insight of detailed balance of angular momentum (in addition to energy) of equilibrium thermal radiation, and paves the way for practical functionalities based on thermal radiation using nonreciprocal bianisotropic materials. [ABSTRACT FROM AUTHOR]

A wide bandgap oxide/transition metal multilayered structure, consisting of four submicron-thick Ga-doped ZnO layers and three ultrathin Co metal layers, is studied to highlight the induction of room temperature ferromagnetism (RTFM), a fundamental outcome of investigations dealing with dilute magnetic semiconductors and multiferroic materials. A comprehensive study including the structural, optical and magnetic properties of both as-deposited and high-temperature annealed samples is described. Optical transmittance spectroscopy and x-ray diffraction measurements confirm the conversion of the layered structure into a solid-state solution of Co within the Ga-doped ZnO after annealing. The study discloses RTFM in the as-deposited state due to nonoxidized metal components within the multilayer structure. [ABSTRACT FROM AUTHOR]

In this report, the ferromagnetic shape memory alloy (Ni50Mn35In15) and Pb0.96La0.04Zr0.52Ti0.48O3 based bilayer (Ni-Mn-In/PLZT (260 nm/300 nm)), trilayer (Ni-Mn-In/PLZT/Ni-Mn-In (130 nm/300 nm/130 nm)) and four-layer (Ni-Mn-In/PLZT/Ni-Mn-In/PLZT (130 nm/150 nm/130 nm/150 nm)) multiferroic heterostructures with equal thickness ratios have been fabricated over Si substrates via DC/RF magnetron sputtering technique. The in-plane and out-of-plane magnetic hysteresis curves show the anisotropic nature of the ferromagnetic layer. The anisotropic magnetoelectric coupling characteristics have been investigated for all the fabricated devices by recording the induced magnetoelectric coupling voltages under both parallel and perpendicular applied magnetic fields to the plane of the device. Compared to all fabricated heterostructures, the trilayer structure exhibits the highest magnetoelectric coupling coefficients with 1.56 V/(cm Oe)-1 and 2.01 V/(cm Oe)-1 in longitudinal and transverse configurations, respectively. This anisotropic nature of magnetoelectric coupling can be used to measure the applied magnetic field direction. The rarely reported anisotropic AC magnetic field sensing parameters of the fabricated devices like Pearson's r, sensitivity, and inaccuracy have been calculated. The trilayer device exhibits excellent AC magnetic field sensing parameters with inaccuracy, sensitivity, and linearity of 1.856% full-scale output (FSO), 0.63 mV cm−1 and 0.9993 in longitudinal configuration while 1.755% FSO, 1.18 mV Oe−1, and 0.9993 in the transverse configuration, respectively. Such nanoscale ferromagnetic shape memory alloys based symmetric multilayered multiferroic heterostructures pave the way for the design and development of futuristic MEMS magnetoelectric magnetic field sensor to detect the magnetic field and its spatial orientation. [ABSTRACT FROM AUTHOR]

Multiferroic materials draw more and more attention due to their potential applications in novel multifunctional instruments and devices. In nanocomposite thin films, the ferroelectric and magnetic orders can be manipulated by orientation and strain, which will affect the multiferroics. In this letter, we reported an epitaxial PbTiO3:ϵ-Fe2O3 composite thin film with 20 nm thickness, which was fabricated on (111)-oriented Nb:SrTiO3 substrate by radio frequency magnetron sputtering method. The nanocomposite film presents both ferroelectric (Pr ≈ 19 µC cm−2) and ferromagnetic (Ms ≈ 25 emu cc−1) properties at room temperature. The combination of PbTiO3 and ϵ-Fe2O3 distinctly reduced the magnetic coercive field of the ϵ-Fe2O3. Piezoresponse force microscopy demonstrated that the composite film possessed excellent uniformity and surface quality, which is significant to the application of multifunctional precision devices. [ABSTRACT FROM AUTHOR]

Organic multiferroic tunnel junctions (OMFTJs) with multi-resistance states have been proposed and have drawn intensive interests due to their potential applications, for example in memristor and spintronics based synapse devices. The ferroelectric control of spin polarization at a ferromagnet/ferroelectric organic (FE-Org) interface by electrically switching the ferroelectric polarization of the FE-Org has been recently realized. However, there is still a lack of understanding of the transport properties in OMFTJs, especially the interplay between the ferroelectric domain structure in the organic barrier and the spin polarized electron tunneling through the barrier. Here, we report on a systematic study of the temperature dependent transport behavior in La0.6Sr0.4MnO3/PVDF/Co OMFTJs. It is found that thermal fluctuation of the ferroelectric domains play an important role on the transport properties. When T > 120 K, the opposite temperature dependence of resistance for up and down ferroelectric polarization states results in a rapid diminishing of the tunneling electroresistance. These results contribute to the understanding of the transport properties for designing high performance OMFTJs for memristor and spintronics applications. [ABSTRACT FROM AUTHOR]

The piezoelectric, ferromagnetism, and magnetoelectric response of BiFeO3–BaTiO3 ceramics with the compositions around the morphotropic phase boundary (MPB) of the solid solution are systematically investigated after the ceramics have been quenched from a high temperature. We find that the ferromagnetism of the quenched ceramics is greatly enhanced. An enhanced piezoelectric response d33 larger than 200 pC/N, which could be sustained up to 350 °C, is measured. As a result of enhanced ferromagnetism and piezoelectric response, a large magnetoelectric response ∼ 1.3 V/cm·Oe (1 Oe = 79.5775 A·m−1) is obtained near the mechanical resonance frequency of the quenched ceramic samples. Our research also shows that in addition to the ferromagnetism and piezoelectric response, the mechanical quality factor is another important parameter to achieve high magnetoelectric response because the physical effects are coupled through mechanical interaction in BiFeO3-based materials. Our work suggests that quenching is an effective approach to enhancing the magnetoelectric response of BiFeO3-based materials and the materials belong to single-phase multiferroic materials with high magnetoelectric response. [ABSTRACT FROM AUTHOR]

The multicaloric effect refers to the thermal response of a solid material driven by simultaneous or sequential application of more than one type of external field. For practical applications, the multicaloric effect is a potentially interesting strategy to improve the efficiency of refrigeration devices. Here, the state of the art in multi-field driven multicaloric effect is reviewed. The phenomenology and fundamental thermodynamics of the multicaloric effect are well established. A number of theoretical and experimental research approaches are covered. At present, the theoretical understanding of the multicaloric effect is thorough. However, due to the limitation of the current experimental technology, the experimental approach is still in progress. All these researches indicated that the thermal response and effective reversibility of multiferroic materials can be improved through multicaloric cycles to overcome the inherent limitations of the physical mechanisms behind single-field-induced caloric effects. Finally, the viewpoint of further developments is presented. [ABSTRACT FROM AUTHOR]

A new sol-foam-gel method was developed to fabricate La-doped BiFeO3 multiferroic materials. It was demonstrated that a gradual increase in the content of La-doped into BiFeO3 results in its structure changing from rhombohedral to orthorhombic. A study of other property changes indicates that La-doping in BiFeO3 enhances its ferromagnetism and ferroelectricity. A temperature-dependent magnetization study suggests that the magnetic property of La-doped BiFeO3 samples varied from antiferromagnetic to ferromagnetic as the content of La-doped into BiFeO3 increased from 0 to 20%. Unique temperature-dependent zero field cooling (ZFC) and field cooling (FC) magnetization behaviors were observed in 15% La-doped BiFeO3 — its ZFC temperature-dependent magnetization being ferromagnetic and its FC temperature-dependent magnetization being antiferromagnetic. A possible mechanism of such an interesting M–T behavior is discussed. [ABSTRACT FROM AUTHOR]

Bi0.9Ho0.1Fe0.95O3 and Bi0.9Ho0.1Fe0.9Ti0.05O3 ceramics were prepared and compared to reveal the effects of Ho and Ti codoping in BiFeO3. X-ray diffraction indicated that both ceramics had a high rhombohedral perovskite phase content, and microstructural analyses showed that the grains of the Bi0.9Ho0.1Fe0.9Ti0.05O3 ceramics were much smaller than those of Bi0.9Ho0.1Fe0.95O3. An electrical resistivity of more than 1 × 1014 Ω · cm at room temperature, and a magnetic hysteresis loop with a remnant magnetization 2Mr of ∼ 0.485 emu/g were obtained for Bi0.9Ho0.1Fe0.9T0.05O3; both were much higher than those of Bi0.9Ho0.1Fe0.95O3. Changes in the defect subsystem of BiFeO3 induced by Fe-deficiency and (Ho,Ti) codoping are proposed as being responsible for the improvement in the properties. [ABSTRACT FROM AUTHOR]

We report photovoltaic (PV) effect in multiferroic Bi0.9Sm0.1Fe0.95Co0.05O3 (BSFCO) thin films. Transition metal modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD). PV response is observed under illumination both in sandwich and lateral electrode configurations. The open-circuit voltage (Voc) and the short-circuit current density (Jsc) of the films in sandwich electrode configuration under illumination are measured to be 0.9 V and −0.051 µA cm−2. Additionally, we report piezoresponse for BSFCO films, which confirms ferroelectric piezoelectric behaviour. [ABSTRACT FROM AUTHOR]

The phase formation behaviour of the magnetoelectric multiferroic 0.8BiFeO3–0.2PbTiO3 was studied as a function of heat treatment at different temperatures of a sol–gel derived powder. While under ordinary synthesis conditions this composition exhibits antiferromagnetic ordering and a rhombohedral structure; the sol–gel-enabled low-temperature synthesis could stabilize a tetragonal metastable phase along with the stable rhombohedral phase, mimicking a morphotropic phase boundary state. The phase coexistence state exhibits relatively enhanced ferromagnetic correlation. The same system with a relatively higher PbTiO3 concentration, 0.65BiFeO3–0.35PbTiO3, on the other hand, exhibits a rhombohedral metastable phase. These results suggest that the occurrence of metastable phases is a very common feature in the BiFeO3–PbTiO3 magnetoelectric ferroelectric system and that it affects the ferroelectric and magnetic properties of system quite remarkably. [ABSTRACT FROM AUTHOR]

The interfacial magnetoelectric effect and the critical thickness for the ferroelectric in half-metallic ferromagnet/ferroelectric Co2FeSi/BaTiO3 multiferroic tunnel junctions are investigated using a first-principles density-functional theory. The magnetoelectric effect is derived from the difference of the magnetic moments on interfacial atoms, which are sensitive to the polarization of ferroelectric layers in multiferroic tunnel junctions. Besides this, the coupling is found to be dependent on the interfacial electronic hybridizations and to be affected by the choice of the atomic termination. In addition, the magnetoelectric coefficients calculated for the FeSi/TiO2 and Co2/TiO2 interfaces of the junctions are different from each other. Meanwhile, the critical thickness of ferroelectric state was found to be about 1.7 nm in the Co2/TiO2 interface but vanished in the FeSi/TiO2 interface. The half-metallic ferromagnetic/ferroelectric tunnel junctions may open a promising avenue for designing novel electronic and spintronic devices at nanoscale. [ABSTRACT FROM AUTHOR]

(NH4)2[FeCl5(H2O)], a member of the family of antiferromagnetic A2[FeX5(H2O)] compounds (X = halide ion and A = alkali metal or ammonium ion) is classified as a new multiferroic material. We report the onset of ferroelectricity below ≃6.9 K within an antiferromagnetically ordered state (TN ≃ 7.25 K). The corresponding electric polarization can drastically be influenced by applying magnetic fields. Based on measurements of pyroelectric currents, dielectric constants and magnetization we characterize the magnetoelectric, dielectric and magnetic properties of (NH4)2[FeCl5(H2O)]. By combining these data with measurements of thermal expansion, magnetostriction and specific heat, we derive detailed magnetic field versus temperature phase diagrams. Depending on the direction of the magnetic field up to three different multiferroic phases are identified, which are separated by a magnetically ordered, but non-ferroelectric phase from the paramagnetic phase. Besides these low-temperature transitions, we observe an additional phase transition at ≃79 K, which we suspect to be of structural origin. [ABSTRACT FROM AUTHOR]

(Bi3.15Nd0.85)(Ti2Fe0.5Co0.5)O12−δ ceramics were prepared by the conventional solid-state reaction method. The sample of the layered perovskite phase was successfully obtained. The measurement of x-ray photoelectron spectroscopy indicated the coexistence of Fe3+ and Fe2+ ions. The multiferroic behaviour of the sample at room temperature (RT) was demonstrated by the ferroelectric (2Pr = 8 µC cm−2, 2Ec = 64 kV cm−1 at applied electric field 86 kV cm−1) and ferromagnetic (2Mr = 32 m emu g−1, 2Hc = 872 Oe at applied magnetic field 1.1 T) hysteresis loops. Remarkably, a clearly identified positive magnetocapacitance effect was observed with a large magnetocapacitance value of ∼14.2% at 30 kHz. Comparison of the impedance Cole–Cole plots measured with and without magnetic field revealed that the occurrence of magnetocapacitance effect is accompanied by an increase in the conductivity under magnetic field, which is explained by the enhancement of electron jumping in Fe2+–O–Fe3+ chains by magnetic field. The present results suggest a new candidate for a RT multiferroic material with large magnetocapacitance effect. [ABSTRACT FROM AUTHOR]

Bipolar resistive switching is studied in BiFe0.95Zn0.05O3 films prepared by pulsed laser deposition on (001) SrTiO3 substrate, with LaNiO3 as the bottom electrode, and Pt as the top electrode. Multiple steps of resistance change are observed in the resistive switching process with a slow voltage sweep, indicating the formation/rupture of multiple conductive filaments. A resistive ratio of the high resistance state (HRS) to the low resistance state (LRS) of over three orders of magnitude is observed. Furthermore, the conduction mechanism is confirmed to be space-charge-limited conduction with the Schottky emission at the interface with the top Pt electrodes in the HRS, and Ohmic in the LRS. Impedance spectroscopy demonstrates a conductive ferroelectric/interfacial dielectric 2-layer structure, and the formation/rupture of the conductive filaments mainly occurs at the interfacial dielectric layer close to the top Pt electrodes. [ABSTRACT FROM AUTHOR]

The coexistence of bi-relaxor property, i.e. ferroelectric relaxor as well as spin glass type behaviour, is observed in disordered multiferroic ceramic 0.70Bi0.90Ca0.10FeO3–0.30PbTiO3. The real parts of dielectric permittivity and magnetic susceptibility show pronounced frequency dispersion near the corresponding phase transition temperatures, namely, Tc ≈ 550K and TN ≈ 110 K, respectively. The relaxor behaviour observed in temperature-dependent dielectric constant measurement is confirmed by fitting of the Vogel–Fulcher equation. Similarly, magnetic spin glass behaviour is proven by power law fitting. The origin of such bi-relaxor in the present system can be attributed to the disorder and frustration among the uncompensated spins of the Fe-ion. This has been confirmed by analysing the x-ray photoelectron (XPS) spectrum of the sample under investigation. Using FESEM micrographs, the coexistence of nano-sized and bulk grains is shown. The importance of such coexistence is discussed and also presented in the paper. [ABSTRACT FROM AUTHOR]

A generalized thermodynamic theory of giant-caloric effects in coupled multiferroic solids is introduced. The generalized theory allows analytical derivation of any caloric effect in solids displaying any type of cross coupling. In the particular cases of the non-coupled ferroic materials, the theory reproduces the well-known formulae describing magnetocaloric, electrocaloric or elastocaloric effects. This work facilitates adequate modeling tools and analytical relations capable of predicting caloric effects in complex coupled multiferroic materials, which is very beneficial to future developments in solid-state cooling technologies. [ABSTRACT FROM AUTHOR]

Heterostructures with magneto-electro-elastic coupling (e.g. multiferroics) are of paramount importance for developing new sensors, actuators and memories. With the progressive miniaturization of these systems it is necessary to take into account possible thermal effects, which may influence the normal operating regime. As a paradigmatic example we consider a recently introduced non-volatile memory element composed of a magnetostrictive nanoparticle embedded in a piezoelectric matrix. The distributions of the physical fields in this matrix/inclusion configuration are determined by means of the Eshelby theory, the magnetization dynamics is studied through the Landau–Lifshitz–Gilbert formalism, and the statistical mechanics is introduced with the Langevin and Fokker–Planck methodologies. As result of the combination of such techniques we determine the switching time between the states of the memory, the error probability and the energy dissipation of the writing process. They depend on the ratio kBT/v where T is the absolute temperature and v is the volume of the magnetoelastic particle. [ABSTRACT FROM AUTHOR]

Bi0.7Dy0.3FeO3 (BDFO) exhibiting multiferroicity at room temperature is used as a core material for the first time to fabricate a ring-type inductor. More importantly due to the presence magnetoelectric coupling, the BDFO inductor could be tuned magnetically as well as electrically. It is observed that tunability of this inductor is better in the presence of magnetic field than electrical field. This behaviour is correlated to high electrical loss factor (tan δ) of the core material. The dissipation of electrical energy perhaps impedes the strain induced change in permeability. However, there are chances of improvement if tan δ of BDFO is controlled. Nevertheless, simplicity in fabrication and flexibility in operation make tunable BDFO inductors attractive for novel applications. The results give confidence to work on development of miniaturization of BDFO inductor. [ABSTRACT FROM AUTHOR]

Magnetic/piezoelectric multiferroic heterostructures with strong magnetoelectric (ME) coupling have recently attracted considerable interest. Since the ratio of magnetostriction λs over saturation magnetization Ms is a key factor to achieve strong magnetoelectric coupling in ferrite/piezoelectric multiferroic heterostructures, here we find a solution to tune λs/Ms by aluminum doping. We report aluminum-substituted NiZn-ferrites with different compositions (Ni0.65Zn0.35Fe2−xAlxO4, x = 0, 0.1, 0.3, 0.4, 0.6, 0.8 and 1) fabricated by a solid-state sintering process. The saturation magnetization of these NiZnAl-ferrites was reduced from 6000 to 900 G with increased Al doping, which was accompanied by a significantly narrowed ferromagnetic resonance linewidth from 1870 to 340 Oe. Meanwhile, saturation magnetostriction of these NiZnAl-ferrites was reduced from 6.67 to 1.40 ppm with increased amount of Al doping. Strong ME coupling was demonstrated in the NiZnAl-ferrites/PZT multiferroic heterostructures. A large piezoelectric deformation induced ferromagnetic resonance field change up to 42 Oe was observed in Ni0.65Zn0.35Fe1.2Al0.8O4/PZT heterostructures, corresponding to a large microwave ME coefficient of 4.2 Oe cm kV−1. These AlNiZn-ferrites and NiZnAl-ferrites/PZT heterostructures with large ME coupling provide a great opportunity for electrical tuning microwave devices. [ABSTRACT FROM AUTHOR]

The 0.6(Bi1-xLax)FeO³-0.4SrTiO3 (x = 0, 0.1) multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO³ and La in BiFeO³. The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure. The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO³ and substitution of La. The values of the dielectric constant εr and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature. The La-doped 0.6BiFeO³-0.4SrTiO³ ceramics exhibit improved dielectric and ferroelectric properties, with higher dielectric constant enhanced remnant polarization (Pr) and lower leakage current at room temperature. Compared with a anti-ferromagnetic BiFeO³ compound, the 0.6(Bi0.9La0.1)FeO³-0.4SrTiO³ sample shows the optimal ferromagnetism with remnant magnetization Mr ~ 0.135 em&#mgr;/g and ferroelectricity with Pr ~ 5.94 &#mgr;C/cm2 at room temperature. [ABSTRACT FROM AUTHOR]

The semi-quantum two-orbital exchange model is used to investigate the effect of small rare-earth ion substitution on orthorhombic RMnO³ with A-type antiferromagnetic order, using the Monte Carlo algorithm, exact diagonalization, and zero-temperature optimization approaches. It is revealed that the substitution results in a rich multiferroic phase diagram where the coexisting A-type antiferromagnetic phase and spiral spin phase, pure spiral spin phase, coexisting spiral spin phase, the E-type antiferromagnetic phase, and the pure E-type antiferromagnetic phase emerge in sequence. The multiferroic phase transitions modulate substantially the electric polarization, which is consistent qualitatively with recent experiments. [ABSTRACT FROM AUTHOR]

The complete magnetic and multiferroic phase diagram of Mn1-xCoxWO4 single crystals is investigated by means of magnetic, heat capacity and polarization experiments. We show that the ferroelectric (FE) polarization E P in the multiferroic state abruptly changes its direction twice upon increasing Co content, x. At xc1 = 0.075, E P rotates from the b-axis into the a-c-plane and at xc2 = 0.15 it flips back to the b-axis. The origin of the multiple polarization flops is identified as an effect of the Co anisotropy on the orientation and shape of the spin helix leading to thermodynamic instabilities caused by the decrease of the magnitude of the polarization in the corresponding phases. A qualitative description of the FE polarization is derived by taking into account the intrachain (c-axis) as well as the interchain (a-axis) exchange pathways connecting the magnetic ions. In a narrow Co concentration range (0.1 ⩽ x ⩽ 0.15), an intermediate phase, sandwiched between the collinear hightemperature and the helical low-temperature phases, is discovered. The new phase exhibits a collinear and commensurate spin modulation similar to the low-temperature magnetic structure of MnWO4. [ABSTRACT FROM AUTHOR]

The complete magnetic and multiferroic phase diagram of Mn1-xCoxWO4 single crystals is investigated by means of magnetic, heat capacity and polarization experiments. We show that the ferroelectric (FE) polarization E P in the multiferroic state abruptly changes its direction twice upon increasing Co content, x. At xc1 = 0.075, E P rotates from the b-axis into the a-c-plane and at xc2 = 0.15 it flips back to the b-axis. The origin of the multiple polarization flops is identified as an effect of the Co anisotropy on the orientation and shape of the spin helix leading to thermodynamic instabilities caused by the decrease of the magnitude of the polarization in the corresponding phases. A qualitative description of the FE polarization is derived by taking into account the intrachain (c-axis) as well as the interchain (a-axis) exchange pathways connecting the magnetic ions. In a narrow Co concentration range (0.1 ⩽ x ⩽ 0.15), an intermediate phase, sandwiched between the collinear hightemperature and the helical low-temperature phases, is discovered. The new phase exhibits a collinear and commensurate spin modulation similar to the low-temperature magnetic structure of MnWO4. [ABSTRACT FROM AUTHOR]

Bi5Fe1-xCoxTi3O15 (x = 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8) multiferroic ceramics are synthesized in two steps using the solid state reaction technique. X-ray diffraction patterns show that the samples have four-layer Aurivillius phases. At room temperature (RT), the samples each present a remarkable coexistence of ferromagnetism (FM) and ferroelectricity (FE). The remnant polarization (2Pr) reaches its greatest value of 14 µC/cm2 at x = 0.6. Remnant magnetization (2Mr) first increases and then decreases, and the greatest 2Mr is 7.8 menu/g when x = 0.5. The magnetic properties for x = 0.4 are similar to those for x = 0.6, indicating that the magnetic properties originate mainly from the coupling between Fe3+ and Co3+ ions, rather than from their own magnetic moments. [ABSTRACT FROM AUTHOR]

We report magnetic properties of electrospun multiferroic nanofibers assembled into linear aggregates with an external magnetic field, and measured with the magneto-optical Kerr effect (MOKE) in a non-specular or scattering geometry (ScMOKE). Compared with bulk magnetometry, ScMOKE’s sensitivity to subtle differences between aggregates offers a route to determine local multiferroic coupling in disordered nanomaterials. CoFe2O4-BaTiO3 nanofiber agglomerates are assembled prior to measurement by suspending and aligning the fibers in a transparent air-cured polyvinyl alcohol solution. We detect the polarization change in light scattered from the fibers, collected at an off-specular angle in order to eliminate the background caused by substrate reflection. Averaged hysteresis loops from different agglomerates show a variety of unique structures. For our optical spot size of  ∼15 m, multiple fibers, within a single agglomerate, are detected simultaneously, suggesting ScMOKE can distinguish local magnetization reversal fields that vary from fiber to fiber, as well as magnetic interactions between fibers. [ABSTRACT FROM AUTHOR]

The present study explores the systematic investigation of magnetoelectric coupling and magnetic field sensing characteristics of 2–2 layered Ni50Mn35In15/Pb0.96La0.04(Zr0.52Ti0.48) O3 (Ni–Mn–In/PLZT) multiferroic heterostructure fabricated over Si substrate via DC/RF magnetron sputtering technique. The temperature-dependent dielectric constant curve depicts a typical hump-like structure in the temperature range of 266–283 K, which overlaps with the Ni–Mn–In martensite transformation region. The magnetoelectric coupling coefficient (αME) as a function of crucial factors such as DC bias magnetic field, AC magnetic field and its frequency are also analyzed and well explained. A αME of ~1.2 V cm−1 Oe is observed at ~400 Oe bias magnetic field. The multiferroic heterostructure exhibits excellent magnetic field sensing parameters with sensitivity, correlation coefficient (r2), hysteresis and inaccuracy of ~0.58 mV Oe−1, 0.9992, 1.46% full-scale output (FSO) and 2.4% FSO, respectively. Such Si-integrated Ni–Mn–In/PLZT thin-film-based multiferroic heterostructures are useful for magnetic field sensing and nanoelectromechanical system device applications at room temperature. [ABSTRACT FROM AUTHOR]

Room-temperature electric field control of magnetization is of interest for the potential application of low consumption nonvolatile memory. Here, we report the realization of electric field modulation of magnetization in a single phase multiferroic material Ba0.5Sr1.5Co2Fe11AlO22. In this work, we use static and dynamic measurements to reveal the magnetoelectric coupling between magnetization (M) and polarization (P). At the temperature of 10 K, the first order magnetoelectric (ME) term is dominated and the magnetization linearly changes with the electric field. While at room temperature, the quadratic term become apparent, leading to symmetric butterfly-like P–H and M–E curves. Our study reveals that an alternating longitudinal conical (ALC) phase induced exchange interaction may exist in Y type hexaferrite Ba0.5Sr1.5Co2Fe11AlO22 and contribute to the ME coupling mechanism. [ABSTRACT FROM AUTHOR]

In this study, the design and development of a low cost and fully automated in situ temperature dependent magneto-dielectric experimental setup has been reported. The setup has been designed to measure the effect of magnetic field on the dielectric constant of the material as a function of frequency and temperature. Measurements can be carried out over a temperature range from 120 K to 350 K, frequency range from 20 Hz to 5 MHz, and maximum magnetic field up to 2.2 Tesla. To monitor the measurement online a computer controlled graphical user interface (GUI) has also been developed based on QT C  +  + creator, an open source platform. The magneto-dielectric effect has been demonstrated in GaFeO3, LaFe0.3Ga0.7O3, and YFeO3 samples. The developed magneto-dielectric measurement setup will provide a platform to understand the physics of magneto-dielectric and multiferroic materials under the influence of the magnetic field at different frequencies and temperatures. [ABSTRACT FROM AUTHOR]

A type of synaptic devices have been constructed by employing the nonlinear magnetoelectric effects in multiferroic materials. The state of the magnetoelectric coefficient of the device can be tuned continuously with a large number of nonvolatile levels by engineering the applied electric-field pulses. Therefore, the magnetoeletric coefficient may be regarded as the synaptic weight, and the subsequent magnetoelectric voltage VME acts as excitatory or inhibitory postsynaptic potentials. Synaptic behaviors including the long-term potentiation, long-term depression, and spiking-time-dependent plasticity have been demonstrated in a multiferroic heterostructure made of Metglas/PMN-PT/Metglas. The consumed energy density is estimated to be ~7.7 mJ cm−3 per spike, comparable to the biological synapse in the brain. Our work presents an alternative way towards artificial synaptic devices with very low energy consumption. [ABSTRACT FROM AUTHOR]

Elastic properties are important in fundamental understanding of multiferroic materials. However, up to now, there is no work about anisotropy of elastic properties in orthorhombic Ca3Mn2O7. In this study, using coordinate transformation method, we investigated basic elastic parameters (elastic constants ) and engineering elastic parameters (Youngʼs modulus , Poissonʼs ratio , and the rigidity modulus ) of orthorhombic Ca3Mn2O7 along arbitrary orientations. The detailed anisotropic characteristics of these parameters were presented. The results reveal the orientation related elastic properties in mm2 point group orthorhombic Ca3Mn2O7. [ABSTRACT FROM AUTHOR]

The multiferroicity in the RMn2O5 family remains unclear, and less attention has been paid to its dependence on high-temperature (high-T) polarized configuration. Moreover, no consensus on the high-T space group symmetry has been reached so far. In view of this consideration, one may argue that the multiferroicity of RMn2O5 in the low-T range depends on the poling sequence starting far above the multiferroic ordering temperature. In this work, we investigate in detail the variation of magnetically induced electric polarization in GdMn2O5 and its dependence on electric field poling routine in the high-T range. It is revealed that the multiferroicity does exhibit qualitatively different behaviors if the high-T poling routine changes, indicating the close correlation with the possible high-T polarized state. These emergent phenomena may be qualitatively explained by the co-existence of two low-T polarization components, a scenario that was proposed earlier. One is the component associated with the Mn3+–Mn4+–Mn3+ exchange striction that seems to be tightly clamped by the high-T polarized state, and the other is the component associated with the Gd3+–Mn4+–Gd3+ exchange striction that is free of the clamping. The present findings may offer a different scheme for the electric control of the multiferroicity in RMn2O5. [ABSTRACT FROM AUTHOR]

We report the electronic structure studies of well-characterized La0.8Bi0.2Fe1−xMnxO3 (LBFM, 0.0 ⩽ x ⩽ 0.4) multiferroic samples investigated by soft x-ray absorption spectroscopy at O K-, Mn L3,2-, Mn K-, Fe L3,2- and La M4,5-edges along with the spectra of reference compounds. The investigations are performed to find out the chemical states and crystal field symmetry of ions present in the LBFM multiferroic samples after the substitution of Mn ions at Fe sites. Studies reveal a slight shift in the peak positions of O K-edge spectra along with growth in intensities of low-energy features. An analysis of the Mn L3,2- and K-edge, in addition to the comparison with the spectra of reference compounds, indicates that the Mn ions are present in mixed valence states. It is found that the Mn ions are mainly in +3 states along with a small contribution of +2 and +4 ones. The study of Fe L3,2-edge confirms the trivalent state of Fe ion. M4,5-edges of La corroborate the +3 state of La in the system. Atomic multiplet calculations are also performed on Fe L3,2-, Mn L3,2- and La M4,5-edges to further verify the valency, symmetry and the crystal field splitting. [ABSTRACT FROM AUTHOR]

The need for increasingly powerful computing hardware has spawned many ideas stipulating, primarily, the replacement of traditional transistors with alternate ‘switches’ that dissipate miniscule amounts of energy when they switch and provide additional functionality that are beneficial for information processing. An interesting idea that has emerged recently is the notion of using two-phase (piezoelectric/magnetostrictive) multiferroic nanomagnets with bistable (or multi-stable) magnetization states to encode digital information (bits), and switching the magnetization between these states with small voltages (that strain the nanomagnets) to carry out digital information processing. The switching delay is ∼1 ns and the energy dissipated in the switching operation can be few to tens of aJ, which is comparable to, or smaller than, the energy dissipated in switching a modern-day transistor. Unlike a transistor, a nanomagnet is ‘non-volatile’, so a nanomagnetic processing unit can store the result of a computation locally without refresh cycles, thereby allowing it to double as both logic and memory. These dual-role elements promise new, robust, energy-efficient, high-speed computing and signal processing architectures (usually non-Boolean and often non-von-Neumann) that can be more powerful, architecturally superior (fewer circuit elements needed to implement a given function) and sometimes faster than their traditional transistor-based counterparts. This topical review covers the important advances in computing and information processing with nanomagnets, with emphasis on strain-switched multiferroic nanomagnets acting as non-volatile and energy-efficient switches—a field known as ‘straintronics’. It also outlines key challenges in straintronics. [ABSTRACT FROM AUTHOR]

The present work reports the impact of the oxygen vacancies (OVs) created in multiferroic BiFe0.83Ni0.17O3 in both a qualitative and quantitative manner by employing first principles density functional theory calculations. We have investigated the role of OVs in modulating the structural and optical properties of BiFe0.83Ni0.17O3. Our results have shown that the higher concentration of OVs increases the electron hopping process which ultimately results in the presence of Fe2+ and Fe3+ and the increasing trend of lattice parameters is due to the existence of larger ionic radius Fe2+ in addition to Fe3+ ions. More distortion was realized for the NiO6 octahedron when the OVs were created farther from the Ni ion resulting in changes in the electronic state by decreasing band gaps and providing conductivity. Considerably less distortion was observed when OVs were created nearer to the Ni ion, increasing the band gap values in both up and down spin channels. With respect to optical properties, we conclude that OVs, when created nearer to the Ni ion, increase the absorption behavior in a significant manner. The observed refractive index values are known to be one of the highest values known in the UV-visible range of the spectrum and thus the existence of OVs can drive this material towards applications in optical communication devices. The maximum dielectric constant values of 9–10.5 are observed in all the configurations in the UV and visible region of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

Quantum entanglement represents a fundamental feature of quantum many-body systems. We combine tripartite entanglement with quantum renormalization group theory to study the quantum critical phenomena. The Ising model and the Heisenberg X X Z model in the presence of the Dzyaloshinskii–Moriya interaction are adopted as the research objects. We identify that the tripartite entanglement can signal the critical point. The derivative of tripartite entanglement shows singularity as the spin chain size increases. Furthermore, the intuitive scaling behavior of the system selected is studied and the result allows us to precisely quantify the correlation exponent by utilizing the power law. [ABSTRACT FROM AUTHOR]

A model is developed for magnetoelectric (ME) interactions in coaxial nanofibers of hexagonal ferrites and ferroelectrics. Multiferroic nanocomposites with hexagonal ferrites are of interest for achieving strong ME coupling under zero external magnetic bias due to their high uniaxial or planar anisotropy fields. In this work we considered the ME coupling in core–shell fibers of lead zirconate titanate (PZT) and ferrimagnetic W- and Y-type hexagonal ferrites with high magnetostriction and piezomagnetic coupling. Modeling of the direct-ME effects, i.e. sample response to an applied magnetic field, is done in terms of the ME voltage coefficients (MEVCs) at low frequencies and at electromechanical resonance (EMR). The converse-ME effect, response of the fibers to an applied DC electric field, is considered at ferromagnetic resonance (FMR). Expressions have been obtained for MEVCs at low frequency and EMR, and for the converse-ME coefficient at FMR. The theory predicts strongest direct-ME coupling in fibers of Ni2Y-PZT and the weakest coupling in Zn2Y-PZT. The MEVC at EMR is one to two orders of magnitude higher than at low frequency and the peak MEVC remains the same for fibers of ferrite core-PZT shell as for PZT core-ferrite shell. The converse-ME effect is expected to be the strongest for fibers of Co2W-PZT and weakest in Ni2Y-PZT. The model has been extended to include an assembled array of core–shell fibers and weakening of the ME coupling is predicted in such arrays due to magnetic and electric dipole–dipole interactions. The theory presented here is of importance for self-biased sensors of low frequency and RF magnetic fields. [ABSTRACT FROM AUTHOR]

Y-type hexaferrites are promising single-phase multiferroics where the electric polarization is induced by conical spin orders. The influence of substitution of Sr and Ni on the magnetic and magnetoelectric properties of Y-type hexaferrite BaSrCo2Fe11AlO22 has been investigated. Sr doping does not change much the Curie temperature TC near 760 K and the saturation magnetization at 300 K. In contrast, the saturation magnetization is reduced by Ni doping. The spin-induced electric polarization can be reversed by a low magnetic field for all samples, and the doping has almost no influence on the magnetoelectric coefficient at room temperature. The magnetoelectric phase diagrams of all samples have been obtained by the measurements of magnetic field dependence of the dielectric constant at selected temperatures. Both Sr and Ni doping broaden the region of ferroelectric phase by driving the phase boundary to higher magnetic fields. [ABSTRACT FROM AUTHOR]

In this contribution to the special issue on magnetoelectrics and their applications, we focus on some single phase multiferroics, which have been theoretically predicted and/or experimentally discovered by the authors in recent years. In these materials, iron is the common core element. However, these materials are conceptually different from the mostly-studied BiFeO3, since their ferroelectricity is improper. Our reviewed materials are not simply repeating one magnetoelectric mechanism, but cover multiple branches of improper ferroelectricity, including the magnetism-driven ferroelectrics, geometric ferroelectric, as well as electronic ferroelectric driven by charge ordering. In this sense, these iron-based improper ferroelectrics can be an encyclopaedic playground to explore the comprehensive physics of multiferroics and magnetoelectricity. Furthermore, the unique characteristics of iron’s 3d orbitals make some of their magnetoelectric properties quite prominent, comparing with the extensively-studied Mn-based improper multiferroics. In addition, these materials establish the crossover between multiferroics and other fields of functional materials, which enlarges the application scope of multiferroics. [ABSTRACT FROM AUTHOR]

In this work, the effects of Ni substitution on the electrical leakage and multiferroic properties of GaFeO3 were examined. Structural analysis of grown ceramics using x-ray diffraction and Raman shows that all ceramics have pure phases with an orthorhombic structure and space group. Ni substitutions slightly modify lattice parameters and induce lattice distortion within the same crystalline structure. It is observed that with increasing Ni-content up to 0.10, the magnetic transition temperature () increases from 196 K to 407 K. Ni-doped samples showed better ferroelectric properties and a drastic reduction in leakage current (~three orders of magnitude) at room temperature. Enhanced characteristics behavior is observed for 10% Ni substitution (GaFe0.9Ni0.1O3) and higher substitution leads to deterioration of properties with a larger leakage current. It is proposed that the role of Ni substitution can reduce hopping between Fe+3 and Fe+2 as well as suppressing the oxygen vacancies. This work would open new possibilities for integrating polycrystalline GaFeO3 at room temperature for magnetoelectric applications. [ABSTRACT FROM AUTHOR]