Properties Of Multiferroic BiFeO3 Research Articles

Structural, electrical, ferroelastic behavior, and multiferroic properties of BiFeO3

BiFeO3 was synthesized by conventional solid-state reaction method, and its structural, vibrational, electrical, ferroelastic, and multiferroic properties were studied. X-ray diffraction analysis and Rietveld refinement confirmed its rhombohedral crystal structural with the space group of R3c. SEM images show the rectangular shaped micrograins. The stress–strain curves obtained from uniaxial compressive tests with different maximum stresses exhibit hysteresis loops with different remnant strains due to ferroelastic domain switching during compression loading and partial domain switching back upon unloading. From Raman spectra, we have observed 3A1 and 6E modes in the range of 100–600 cm−1. Dielectric constant and dielectric loss were measured as a function of frequency in the range 100 Hz to 1 MHz. The leakage current density was found to be $$8.07\times {10}^{-7}$$ A/cm2 at higher electric field. In further, we performed the ferroelectric, magnetic, and magnetoelectric effect for the confirmation of its multiferroic behavior.

Structural, optical and enhanced multiferroic properties of La/Cr co-substituted BiFeO3 nanostructures

We have synthesized BiFeO3 (BFO) and Bi0.5La0.5Fe1−xCrxO3 (0 ≤ x ≤ 0.06) samples via sol–gel process with the objective to explore the influence of La/Cr co-doping on the structural, optical, dielectric and multiferroic properties of BFO. Rietveld refinement analysis and Raman active modes affirm single-phase and rhombohedral crystal structure of the samples in R3c space group. The UV–visible-DRS data reveal a systematic reduction of the bandgap and increase in the Urbach energy (Eu) with the increase of La/Cr content in BFO matrix. The temperature-dependent dielectric measurements divulge that the BFO has the highest dielectric constant, and relaxation peak shifts with the rise in frequency that proposes the possibility of the thermally activated relaxation mechanism which also supported through the Vogel–Fulcher model. The magnetic hysteresis (M–H) loops exhibit ferromagnetic nature of all the samples at room temperature except BFO. The P–E hysteresis loops display ferroelectric behavior with higher values of polarization and coercive field in the doped samples.

Multiferroic properties and ferroelectric domain structures of Yb-doped BiFeO3 thin films on glass substrates

We investigated the growth characteristics and multiferroic properties of BiFeO3 (BFO) and Yb-doped BiFeO3 (Bi0.85Yb0.15FeO3, YBFO) thin films grown on Pt/Ta/glass substrates. X-ray diffraction experiments showed that both BFO and YBFO thin films had preferentially (111)-oriented polycrystalline structures. Yb doping of BFO thin films led to enhanced multiferroic properties in terms of the ferroelectricity (remanent polarization of about 41.5 μC/cm2) and ferromagnetism (remanent magnetization of about 1.91 emu/cm3). According to piezoresponse force microscopy experiments, the YBFO thin films possessed larger ferroelectric domain structures than the BFO thin films due to the higher domain wall energy of the YBFO thin films.

Effect of Sr and Mn co-doping on multiferroic properties of BiFeO3 via sol-gel chemical process

In this contribution, Sr and Mn co-doped Bi0.90Sr0.10FexMn1 − xO3 (X = 0, 5%, 10%, 15%) nanoparticles were prepared by sol-gel (chemical route) method to observe the dominance of co-substitution on their grain size, morphology, UV-vis absorbance and magnetic properties. Co-substitution of Sr and Mn in BiFeO3, leads to structural transformation from rhombohedral (R3c) to orthorhombic (Pn21a). Field emission scanning electron microscope reveals that upon Mn doping nanoparticles become finer. The M-H loops depict that at 15 mol. % Mn doping the saturation magnetization (Ms) is enhanced significantly. Moreover, the synthesized nanoparticles absorb visible light and their band gaps reduce substantially.

Surface agglomeration is beneficial for release of magnetic property via research of rare earth (RE) element-substitution

BiFeO3 (BFO) thin films and Rare-Earth (RE) element substitutions were successfully fabricated on silicon substrates by sol–gel technology. Multiferroic properties of BFO had been improved considerably on RE (La, Ho, Er)-substitution at Bi site. The RE-substitution principle was presented in Fig. 1(the simulative images of ions matching). The single phase and the perovskite based rhombohedral structure with R3c space group of BFO and RE-substitution films were confirmed through the full pattern fitting of surface and section XRD profiles. There were obvious agglomeration phenomena for RE-substitution films via FESEM patterns, and the AFM images shown that the RE-substation films possessed smoother surface texture comparing with the BFO. The RE-substitution films showed higher saturation magnetization (Ms) and remanent magnetization (Mr) due to the reduced concentration of defects (oxygen vacancy), RE ions with smaller radii size (size effect) and surface structure of compactness. Fe3+ and O2− ions play an essential role in superexchange interaction, the XPS, surface and vertical EDS images revealed increasing tendency of Fe3+ ions and O2− ions.

Structural transitions and multiferrocity in Ba and Co substituted nanosized bismuth ferrite

To investigate the effect of Ba2+ and Co2+ substitution on the multiferroic properties of the BiFeO3 (BFO) ceramic, Bi1-xBaxFe1-yCoyO3 (x = 0,y = 0 and x = 0.2, y = 0,0.015,0.03,0.04,0.05) ceramics were prepared using sol-gel method. Multiferroic properties of BFO have been improved considerably on Ba2+ and Co2+ substitution at Bi and Fe site, respectively. Full pattern fitting of the XRD profile pattern confirmed the structural transition from rhombohedral to pseudo-cubic phase. The magnetisation in BFO rises appreciably and found to be 0.463 emu/g for Bi1-xBaxFe1-yCoyO3 (x = 0.2, y = 0.05) ceramic nanoparticles. The abrupt increase in magnetization for Bi0.8Ba0.2Fe0.95Co0.05O3 is due to anti-ferromagnetic orbital ordering among Fe/Co ions. The orbital ordering among the ions would change the low spin state of the Co2+ ions to high spin state and results in increased magnetization. Beside, the Co substitution is found helpful in reducing the coercivity of the magnetic nanoparticles for their application as magnetic sensors. The Ferroelectric behavior of Ba and Co substituted samples revealed that increase in maximum polarization with increasing Co content is due to interactions among different Jahn-Teller active Co2+ ions. Moreover, the slimmer polarization-electric field (P-E) loops on increasing Co content implying the relaxor ferroelectric behavior of the samples.

Effects of Eu and Ca Co-Substitution for the Improvement of Multiferroic Properties of BiFeO<sub>3</sub>

Pure BiFeO3 (BFO), Ca-doped and Eu/Ca-codoped BFO nanoparticles were prepared by using a sol–gel method. The effects of Eu/Ca-codoped on the structural, magnetic and ferroelectric properties of the samples were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the codoped samples. Co-doped samples were obtained with the best ferromagnetic properties, with the largest remaining magnetization Mr = 0.20 emμ/g. The structure transition may be the main cause for the origin of improved magnetic properties, which destroys the space modulated spin structure of BFO and releases the locked magnetic. In addition, the doping of Eu into BFO can reduce the leakage current and enhance the ferroelectric properties.

Influence of Eu and Sr co-substitution on multiferroic properties of BiFeO3

Pure BiFeO3 (BFO), and Eu-Sr co-substituted BFO samples were prepared by a sol–gel method. The effects of Eu and Sr codoped on the structural, morphological, magnetic and ferroelectric properties were systematically investigated. The X-ray diffraction and Fourier transform infrared spectroscopy reveal that substitution of Eu and Sr at the Bi site results in structural change and single phase formation. The maximum remnant magnetization of 0.287emu/g and coercive field of 10.305kOe are observed in the Bi0.85Eu0.05Sr0.10FeO3 sample. The suppression of spin cycloid caused from the structural distortion can play an important role in the improvement of magnetic properties. The Eu and Sr co-doped samples also exhibit good ferroelectric properties, which may be attributed to suppressing the formation of oxygen vacancies by Eu substitution.

Effect of synthesis route on the multiferroic properties of BiFeO3: A comparative study between solid state and sol–gel methods

Polycrystalline BiFeO3 (BFO) powder was prepared through optimized solid state (SS) and sol–gel (SG) reaction methods. The effect of preparation routes on the crystal purity and multiferroic properties of the BFO was investigated. Sol–gel synthesis results almost a single-phase material at relatively lower temperatures while the solid-state method results into BFO with a small amount of Bi2Fe4O9 secondary phase. The grain size of SG processed sample reduces to half the size of the one that is prepared by SS. Elemental analysis shows a stoichiometric Bi:Fe content for SG samples by restricting the Bi loss. In comparison with the SS samples, dielectric constant of SG samples exhibit higher values with Maxwell–Wagner type dielectric dispersion. A cusp at 50 K was seen in M–T curves for SS samples, for which no frequency dependence was observed in a.c susceptibility measurements ruling out the earlier predictions of spin glass nature in this system. M−H loops show a typical antiferromagnetic nature at 300 K while a weak ferromagnetic behavior is found at 10 K. A slight increase in HC and Mr was observed for SG samples over SS. The improved properties of SG processed BFO makes it more promising for applications.

Effect of A and B-site substitution with Pb, La and Ti on phase stabilization and multiferroic properties of BiFeO3

The work presents a comparative study of the effects of divalent (Pb), trivalent (La) and tetravalent (Ti) substituents on the multiferroic properties of BiFeO3 (BFO). Both A and B-sites were substituted to obtain the compositions i.e. (Bi1−x−yLaxPby)(Fe1−zTiz)O3 (x, y=0, 0.1, 0.2 and z=0, 0.05, 0.1, 0.15). Each of the substituent was particularly chosen i.e. Pb was chosen to keep the lone pair character which is the similar case as Bi ion. Additionally isovalent La was chosen to achieve single phase by reducing Bi volatization. Both these ions, on substitution, stabilized the crystal structure and suppressed the formation of extra phases which are unavoidable in pure BFO. All the Ti substituted and Bi0.8La0.2FeO3 compositions exhibited rhombohedral perovskite (R3c) phase, while Bi0.8Pb0.2FeO3 and Bi0.8La0.1Pb0.1FeO3 exhibited cubic phase. Mössbauer measurements revealed that impurity phase in case of compositions with divalent and trivalent substituents, disappeared completely when Ti substituted Fe. For all the compositions Fe ions were found in +3 state. High temperature dielectric properties showed that all the compositions were ferroelectric with paraelectric transition lying well above the room temperature. Weak ferromagnetism was found in Ti substituted compositions where coercivity was found to increase as the Ti concentration increases. All the BFO samples substituted with Pb, exhibited a dielectric anomaly in the temperature range, 100°C⩽T⩽250°C. A systematic reduction in the intensity of the dielectric anomaly peak was observed as a function of Ti concentration which indicates that the anomaly is related to the conductivity and is element specific. However, Mössbauer data revealed absence of Fe2+ state, which ensured that it was not related with the presence of Fe2+ ions. Saturation polarization was found to increase as Ti concentration increased from 0% to 10%.

Enhancement in the multiferroic properties of BiFeO3 by charge compensated aliovalent substitution of Ba and Nb

Polycrystalline ceramics, Bi1-2xBa2xFe1-xNbxO3 (x = 0.00–0.15), were synthesized by solid state reactions method. X-ray diffraction data have revealed elimination of impurity phases and an increase in unit cell volume with Ba and Nb substitution. Diffraction peak splitting is found to be suppressed which indicates a decrease in octahedral distortion. The Mössbauer spectra demonstrate the suppression of spiral spin modulation of the magnetic moments resulting in enhanced ferromagnetism with increasing dopant concentration. The leakage current density of the sample with x = 0.10 is found to be greatly reduced up to six orders of magnitude as compared to the undoped sample. Ohmic conduction is found to be dominant mechanism in all the samples, however, undoped sample showed space charge limited conduction in high electric filed region, while the sample with x = 0.15 exhibited grain boundary limited conduction in low electric field region.

Multiferroic properties of BiFeO<sub>3</sub>–BaTiO<sub>3</sub> based ceramics

Multiferroic properties of BiFeO<sub>3</sub>–BaTiO<sub>3</sub> based ceramics

Size and Lone Pair Effects on the Multiferroic Properties ofBi0.75A0.25FeO3−δ(A = Sr, Pb, and Ba) Ceramics

The work presents a comparative study of the effects of divalentBa,Sr, andPbsubstituents on the multiferroic properties ofBiFeO3. The multiferroic properties ofBi0.75A0.25FeO3(A = Sr,Pb,Ba) solid solution have been explained taking into account the effects of size differences and electronic configuration differences between the host element (Bi) and the substituent. X‐ray diffraction studies revealed thatSrandPbsubstitution atBi‐site transforms the rhombohedral phase (R3c) to cubic phase (Pm3m), whereas the Ba‐substituted sample exhibited the presence of both rhombohedral and cubic phases (R3c + Pm3m). Electronic structure studies throughXPSrevealed that charge imbalance induced by divalent substitution was being compensated by the formation of oxygen vacancies, while theFeions exist inFe2+andFe3+states. Replacement of volatileBibySr,Pb, andBareduces the concentration of oxygen vacancies (VO2+) and helps to improve the dielectric properties. Strong magnetization enhancement was observed in the substituted compositions and was seen to be consistent with the suppression of cycloid spin structure due to structural transformation as well as possible changes inFe–Olocal environment leading to local lattice distortion effects. Furthermore, the observed decrease in the values of magnetic coercivity at low temperature in all the substituted samples is explained in terms of reduced effective single ion anisotropy, originating in the magnetoelectric coupling and being a particularly stronger effect in the case of the lone pair dopantPb, consistent with theoretical predictions. The lone pair substituentPbleads to the largest dielectric constant, enhanced magnetization, and large effects on the low‐temperature hysteresis.

Structure and multiferroic properties of Bi(1-x)DyxFe0.90Mg0.05Ti0.05O3 solid solution

Chemical modification is proven to be an effective way to improve the properties of perovskite BiFeO3 (BFO). In this paper, we studied the effects of the A-site Dy3+ ion substitution on the structure and multiferroic properties of BFO in which the Fe3+ ion on the B-site is partially co-substituted for by Mg2+ and Ti4+ ions. The solid solution compounds of Bi(1-x)DyxFe0.90Mg0.05Ti0.05O3 (x = 0 – 1) were synthesized by a tartaric acid-assisted solution process, followed by thermal treatments at 850 °C. The structural transition and the ferroelectric and magnetic properties as a function of composition were investigated. It is found that the structure transforms from a rhombohedral (R3c) to an orthorhombic phase (Pn21a) when x is increased to ≥ 0.15. The ferroelectric measurements indicate that the sample with x = 0.15 possesses the best ferroelectric property, and the remnant polarization of the samples with orthorhombic symmetry decreases with the increase of Dy3+ concentration. The compounds of Bi(1-x)DyxFe0.90Mg0.05Ti0.05O3 (x = 0.05 – 1.00) exhibit weakly ferromagnetic properties at low temperatures, but antiferromagnetic behavior at high temperatures. The magnetization of the solid solution increases linearly with the increase of the Dy3+ amount.

Influence of samarium substitution on structural and multiferroic properties of bismuth ferrite ceramics

Bi1−xSmxFeO3 (x = 0·00–0·15) ceramics were synthesised by sol–gel technique at different Sm contents. The structural and multiferroic properties of the samples were investigated. X-ray diffraction studies show that the structure of BiFeO3 (BFO) was changed from rhombohedral R3c to orthorhombic Pnma, and the impurity phases in both were decreased due to samarium substitution. Raman spectra measurement confirms the result that structure transition occurs. Moreover, the substitution of Sm for Bi could obviously affect the Bi–O bond. Vibrating sample magnetometer measurements show that the ferromagnetic property of BFO is improved by Sm substitution due to the suppressed or broken cycloid spin structure caused by the changes in the crystalline structure. Ferroelectric measurements show that Sm substitution improves the polarisation due to the significant decrease in electric leakage of the samples. Therefore, it seems a promising way to improve the multiferroic properties of BFO based materials by Sm substitution.

Effect of (Bi, La)(Fe, Zn)O3 thickness on the microstructure and multiferroic properties of BiFeO3 thin films

The effect of Bi0.90La0.10Fe0.90Zn0.10O3 (BLFZO) thicknesses on the microstructure and multiferroic properties of BiFeO3 (BFO) thin films was investigated, and all bilayered thin films were grown on Pt-coated silicon substrates without any buffer layers by a radio frequency sputtering. A (110) orientation is dominant in all the bilayers, and two grain growth modes are identified in these bilayers by using an atomic force microscope, where different grain growth modes significantly affect their leakage behavior. The dielectric constant (εr) of bilayers gradually increases, and magnetic properties were deteriorated with the addition of BLFZO with a higher εr and a weaker magnetic behavior. An enhanced ferroelectric behavior of 2Pr ∼ 116.2 μC/cm2 and 2Ec ∼ 524 kV/cm could be observed in the BFO/BLFZO bilayered thin film with 80 nm BLFZO layer owing to a higher orientation degree of (110) and an interface coupling together with a lower leakage current density. As a result, electrical properties of BFO could be tailored by modifying the thicknesses of BLFZO.

Effects of magnetic annealing on structure and multiferroic properties of pure and dysprosium substituted BiFeO3

In this work, the effects of magnetic annealing on crystal structure and multiferroic properties of BiFeO3 and Bi0.85Dy0.15FeO3 have been investigated. It is found that the X-ray diffraction patterns of pure BiFeO3 samples are obviously broadened after magnetic annealing, whereas those of Bi0.85Dy0.15FeO3 samples are almost unchanged. Magnetic field annealing did not affect the magnetic properties of these two kinds of samples much. However, ferroelectric properties of the two materials exhibited different behaviors after magnetic field annealing. For pure BiFeO3 samples, the remnant polarizations (Pr) are suppressed; in contrast, for Bi0.85Dy0.15FeO3 samples, Pr is greatly enhanced. Possible mechanisms for the effects of magnetic field annealing have been discussed.

Effect of Eu substitution on the crystal structure and multiferroic properties of BiFeO 3

Single-phase Bi 1− x Eu x FeO 3 (0 ≤ x ≤ 0.3) multiferroic ceramics were prepared to study the effects of Eu substitution on their crystal structure and ferroelectromagnetic behavior. X-ray diffraction studies revealed a sequence of the composition-driven structural phase transitions R3c → Pn2 1 a (occurs at x = 0.2). Magnetic measurements revealed that Eu substitution can effectively induce the appearance of the spontaneous magnetization, which was significantly enhanced upon the composition-driven transition from a rhombohedral to an orthorhombic phase. The leakage current was found to be reduced on increased Eu concentration. The electric hysteresis loops were obtained in the Bi 1− x Eu x FeO 3 ceramics, but the loops were not really saturated. The magnetoelectric coupling in Eu-doped BiFeO 3 was estimated by the changes in the dielectric constant with an external magnetic filed.

Multiferroic properties of BiFeO 3/Bi 4Ti 3O 12 double-layered thin films fabricated by chemical solution deposition

Multiferroic BiFeO 3/Bi 4Ti 3O 12 (BFO/BTO) double-layered film was fabricated on a Pt(111)/Ti/SiO 2/Si(100) substrate by a chemical solution deposition method. The effect of an interfacial BTO layer on electrical and magnetic properties of BFO was investigated by comparing those of pure BFO and BTO films prepared by the same condition. The X-ray diffraction result showed that no additional phase was formed in the double-layered film, except BFO and BTO phases. The remnant polarization (2 P r) of the double-layered film capacitor was 100 μC/cm 2 at 250 kV/cm, which is much larger than that of the pure BFO film capacitor. The magnetization–magnetic field hysteresis loop revealed weak ferromagnetic response with remnant magnetization (2 M r) of 0.4 kA/m. The values of dielectric constant and dielectric loss of the double-layered film capacitor were 240 and 0.03 at 100 kHz, respectively. Leakage current density measured from the double-layered film capacitor was 6.1 × 10 − 7 A/cm 2 at 50 kV/cm, which is lower than the pure BFO and BTO film capacitors.

Structure and multiferroic properties of BiFeO 3 powders

Bismuth ferrite powders were synthesized by a simple sol–gel method at the temperature as low as 450 °C. Single phase BiFeO 3 powders with a rhombohedral perovskite structure were fabricated after Bi–Fe gels were calcined at 450–650 °C. Atomic ratio of Bi to Fe is approximately 1:1 for BiFeO 3 powders, as determined by energy dispersive X-ray spectrometer. BiFeO 3 powders show weak ferromagnetism at room temperature and strong size-dependent magnetic properties, which is different from the linear M– H relationship in BiFeO 3 ceramics. Dielectric anomaly at round 330 °C near the magnetic transition point corresponds to the antiferromagnetic to paramagnetic phase transition, indicating the coupling between polarization and magnetization in BiFeO 3 powders. A reversible ferroelectric phase transformation of BiFeO 3 powders has been detected at 827 °C by a differential thermal analysis.