Multiferroic Properties Of Bi0 Research Articles

Structure, dielectric, and multiferroic properties of Bi0.85Nd0.15Fe0.98Zr0.02O3 in Ba and Ti co-doping

Structure, dielectric, and multiferroic properties of Bi0.85Nd0.15Fe0.98Zr0.02O3 in Ba and Ti co-doping

Multiferroic properties of Bi0.95R0.05FeO3 polycrystalline films on the glass substrates (R = La, Pr, Nd, Sm, and Ho)

Multiferroic properties of Bi0.95R0.05FeO3 films (R = La, Pr, Nd, Sm, and Ho) (BRFO) on glass substrates at reduced formation temperature of 450 °C via pulsed laser deposition have been investigated. XRD result shows that perovskite phase is found for all studied BRFO films, but an additional phase, Bi2Fe4O9, coexists for Ho-doped BFO film. For all BRFO films, a fine microstructure with a flat surface is observed. The studied BRFO polycrystalline films exhibit coexistence of good ferroelectric and ferromagnetic properties. The remanent polarization (2Pr) of 57–113 μC/cm2 and electrical coercive field of 210–384 kV/cm is obtained, while the saturation magnetization (Ms) of 6.6–20.3 emu/cm3 and coercivity of 400–600 Oe is attained. The relationship between 2Pr and the ionic radius of R3+ for the BRFO films indicates that R3+ ionic radius may mainly dominate the polarization of BRFO films. The change of Ms with R is related to the magnetic moment of the doped R3+ ion. Besides, the leakage mechanism of BRFO films with R is also discussed. The result in this study suggests multiferroic properties of Bi0.95R0.05FeO3 polycrystalline films could be well tuned by R.

Effects of Gd and Cr co-doping on multiferroic properties of Bi0.9Gd0.1Fe(1-x)CrxO3 (x = 0−0.08)

Gd and Cr co-doped Bi0.9Gd0.1Fe(1 − x)CrxO3 (x = 0 − 0.08) nanoparticles were synthesized via sol-gel method. Precursor salts of bismuth, iron, gadolinium and chromium were used as starting raw materials. Obtained nanoparticles were annealed at various temperatures between 400 − 700 °C. Optimal properties were found to display at 600 °C. X-ray diffraction (XRD) patterns revealed that the partial substitution of Bi3+ by Gd ions and Fe3+ by Cr ions in BiFeO3 (BFO) resulted in evolution of phase transition from rhombohedral to orthorhombic structure. The average crystallite size was found to vary from 16 to 68 nm depending on doping level. The field emission scanning electron micrographs demonstrated a distinct morphology of spherical and nano-sized particles. Ferroelectric measurements showed a substantial improvement in polarization in doped BFO under an applied field of ± 30 kV/cm. Magnetic properties measured at room temperature showed enhanced ferromagnetic characteristics with increasing doping level of Cr up to 6 % (at.) compared to that of un-doped BFO. An asymmetric shift both in the field and magnetization axes of M-H loops was also observed.

Multiferroic properties of Bi0.89Ho0.08Sr0.03Fe0.97−xMn0.03NixO3 thin films modulated by F–N tunneling effects

Bi0.89Ho0.08Sr0.03Fe0.97−xMn0.03NixO3 (BHSFMNixO) films were prepared via a chemical solution deposition method. X-ray diffraction (XRD) patterns and Raman spectroscopy revealed that BHSFMNixO films showed (100) preferential orientation and the structural transition. The structure of BHSFMNi0.02O was close to the morphotropic phase boundary (MPB) (R3c:H:R3m:R = 1:1). The oxygen vacancies were increased with an increase in Ni2+ doping, and there were many defect dipoles. The BHSFMNixO thin films exhibited an Ohmic or a space-charge-limited conduction (SCLC) mechanism in a low electric field, and the interface-limited Fowler–Nordheim (F–N) tunneling or the trap-assisted F–N tunneling in a high electric field. The interface-limited F–N tunneling effects of BHSFMNi0.01O and BHSFMNi0.02O were due to an interface effect. The large remnant polarizations of BHSFMNi0.01O and BHSFMNi0.02O contributed to the intrinsic polarization and the interface-limited F–N tunneling. The fake polarizations of BHSFMNi0.03O and BHSFMNi0.04O were dominated by the trap-assisted F–N tunneling in which the interface traps helped the carrier tunnel the potential barrier. These results demonstrate that the polarizations of BHSFMNixO are related not only to the structural transformation, but also to the defects and conduction mechanisms.

Correlation between ionic size and valence state of tetra, penta and hexavalent B-site substitution with solubility limit, phase transformation and multiferroic properties of Bi0.875Eu0.125FeO3

We present detailed comparative study of effect of isovalent i.e. Eu+3 substitution at A-site and tetra (Ti+4, Zr+4), penta (V+5) and hexavalent (W+6) substitutions at B-site in BiFeO3. Eu+3 substitution led to phase transformation and exhibited mixed phases i.e. rhombohedral and orthorhombic, while tetravalent substituents (Ti+4 and Zr+4) led to stabilization of cubic phase. In higher valent (i.e. V+5 and W+6) cases solubility limit was significantly reduced where orthorhombic phase was observed as in the case of parent compound. Phase transformation as a consequence of increase in microstrain and chemical pressure induced by the substituent has been discussed. Solubility limit of different B-site dopants i.e. Zr, W and V was extracted to 5%, 2% and 2%, respectively. Extra phases in various cases were Bi2Fe4O9, Bi25FeO40, Bi14W2O27, and Bi23V4O44.5 and their fractional amount have been quantified. Ti was substituted up to 15% and has been observed to be completely soluble in the parent compound. Solubility limits depends on ionic radii mismatch and valance difference of Fe+3 and dopant, in which valance difference plays more dominant role. Solubility limit and phase transformation has been explained in terms of change in bond strength and tolerance factor induced by incorporation of dopant which depend on its size and valence state. Detail optical, dielectric, ferroelectric, magnetic and transport properties of Eu and Ti co-doped samples and selected low concentration B-site doped compositions (i.e. 2%) have presented and discussed. Two d-d transitions and three charge transfer transitions were observed within UV-VIS range. Both change in cell volume for the same phase and transformation in crystal structure affects the band gap. Increase in room temperature dielectric constant and saturation polarization was also found to increase in case of Eu-Ti co-doped samples with increasing concentration of Ti. Substitution of Eu at A-site and Ti at B-site led to observation of weak ferromagnetism. Effect of extra phases on ferroelectricity and transport properties have also been discussed.

Dielectric, ferroelectric and magnetic properties of Bi0.78La0.08Sm0.14Fe0.85Ti0.15O3 ceramics prepared at different sintering conditions

Although BiFeO3 (BFO) has attracted great attention due to its special physical properties as a typical single phase multiferroic material, the application is limited due to the formation of impurities, defects and so forth. Herein, we report improved multiferroic properties of Bi0.78La0.08Sm0.14Fe0.85Ti0.15O3 (BLSFTO) ceramics by combination of co-doping and sintering schedule. BLSFTO multiferroic ceramics were prepared by using the conventional solid state reaction method and the effect of sintering time (2, 5, 10, 20 and 30 h) on the structural, dielectric and multiferroic properties was investigated systematically. The result indicates that stable BLSFTO phase with perovskite structure was formed for all the samples. Only some impurities such as Bi2O4 can be observed when the sintering time is longer than 20 h, indicating that the sintering time can induce structural changes in BLSFTO and too long sintering time can remarkably increase the secondary phases. In addition, the frequency dependent dielectric properties show that sintering time has distinct effect on the frequency stability and the relaxation process. The result demonstrates that the enhanced magnetization, improved dielectric and ferroelectric properties may be correlated with the structural transformation, impurities, oxygen vacancies and grain morphology.

Structural phase transition and multiferroic properties of Bi0.8A0.2Fe0.8Mn0.2O3 (A = Ca, Sr)

The multiferroic BiFeO3 and Bi0.8A0.2Fe0.8Mn0.2O3 (A = Ca, Sr) have been synthesized using direct mechanosynthesis. Detailed investigations were made on the influence of Ca–Mn and Sr–Mn co-substitutions on the structure change, electric and magnetic properties of the BFO. Rietveld refinement on the XRD pattern of the modified samples clarifies the structural transition from R3c:H (parent BiFeO3) to the biphasic structure (R3c: H + Pnma). Scanning electron micrographs confirmed the polycrystalline nature of the materials and each of the microstructure comprised of uniformly distributed grains with less porosity. The dielectric measurements reveal that enhancement in dielectric properties due to the reduction of oxygen vacancies by substitutional ions. Studies of frequency-dependence of impedance and related parameters exhibit that the electrical properties of the materials are strongly dependent on temperature, and bear a good correlation with its microstructure. The bulk resistance (evaluated from impedance studies) is found to decrease with increasing temperature for all the samples. The alternating current (ac) conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. Preliminary studies of magnetic characteristics of the samples reveal enhanced magnetization for Ca–Mn co-substituted sample. The magnetoelectric coefficient as the function of applied dc magnetizing field under fixed ac magnetic field 15.368 Oe is measured and this ME coefficient αME corresponds to induction of polarization by a magnetic field.

Structural and multiferroic properties of Bi0.92−x Ho0.08Sr x Fe0.97Mn0.03O3 thin films

The Bi0.92−x Ho0.08Sr x Fe0.97Mn0.03O3(BHSr x FMO) thin films were deposited on FTO/glass substrates by the sol–gel method. The structure, surface morphologies, and electric properties of the thin films were investigated. The results show that the structure of BHSr x FMO thin films transformed from rhombohedral R3c:H to rhombohedral R3m:R when doped with the Sr2+ ions. When the ferroelectric domain structure of the BHSr x FMO(x = 0.00–0.04) thin films is converted from ferroelectric phase and antiferroelectric phase to ferroelectric phase, the coercive field (E c) increased. This change occurs when the defect dipole of $$ ({\text{Sr}}_{{_{{\text{Bi}}} }}^{{\prime }} - {\text{V}}_{{\text{O}}}^{ \cdot \cdot } )^{ \cdot } $$ of BHSr x FMO thin films increased, which clamps the domain wall motion and changes the directions of spontaneous polarization. In an electric field of 536 kV/cm, the 2P r and 2E c of BHSr3FMO thin film are 81.9 μC/cm2 and 524 kV/cm, respectively. In the magnetic field of 8000 Oe, the magnetization of the BHSr3FMO thin film is 8.34 emu/cm3. The BHSr3FMO thin film shows the great multiferroic properties, which are mainly connected with the rhombohedral structure of R3c:H (51%)/R3m:R(49%) space groups at morphotropic phase boundary.

Structural and multiferroic properties of Bi0.92−xHo0.08CaxFe0.97Mn0.03O3 thin film

Bi0.92−xHo0.08CaxFe0.97Mn0.03O3 (BHCxFMO) thin films were deposited on FTO/glass substrates using chemical solution deposition method. The crystal structure analyzed by X-ray diffraction, Rietveld refinement and Raman spectra reveals the structural transformation from rhombohedral R3c:H to triclinic P1 with co-doping. X-ray photoelectron spectroscopy analysis confirms that oxygen vacancy concentration in BHCxFMO thin films increases with the increase of Ca content due to the charge neutralization with Ca2+ doping at Bi3+ site. The frequency dependence of the dielectric response implies that dipoles of the charged defects rather than electrons/domains mainly contribute to the characteristics of εr and tanδ for BHCxFMO films. Among co-doped thin films, BHC1FMO thin film shows the highly enhanced ferroelectric properties with a giant remnant polarization value (Pr~88.18μC/cm2), which is due to low leakage current in high electric field, improved breakdown characteristic and structure transformation. Moreover, BHC1FMO thin film presents enhanced magnetization (Ms=3.35emu/cm3) in comparison to BFO thin film, which could be attribute to the suppression of spiral spin structure and/or the improvement in the canting angle of antiferromagnetically ordered adjacent planes arising from the disturbance of Fe–O–Fe bond angles due to the structural transformation. Raman results have further confirmed that (Ca, Ho, Mn) co-doping induces significant structural distortion of Fe–O bonds, which may cause internal structure distortion related to the change in bond length of the Fe–O and bond angle of Fe–O–Fe.

Effect of sintering temperature on structure and multiferroic properties of Bi0.825Sm0.175FeO3 ceramics

The Bi0.825Sm0.175FeO3 (BSFO) ceramics were prepared by solid state reaction route and the structural, vibrational, and multiferroic properties of these ceramics was studied. The properties of BiFeO3 (BFO) ceramics at higher sintering temperature i. e. 850 °C were compared to that of ceramic at normal sintering temperature (i. e. 830 °C). The Rietveld-refined structure revealed the rhombohedral R3c symmetry in BFO and a mixed phase symmetry (R3c 38.26% + Pnma 61.74%) in BSFO for ceramics sintered at 830 °C. The formation separate phase of SmFeO3 (Pbnm; 12.16%) along with BSFO (Pn21a; 87.84%) phase was observed for ceramics sintered at 850 °C. The small change in sintering temperature led to changes in Raman spectra accompanying abrupt changes in ferroelectric properties. The BSFO shows strong ferromagnetic characteristic due to the spin canting in bulk BFO. The net macroscopic magnetization in bulk BFO due to Sm doping exist due to suppression of spin modulated spiral structure. The BSFO ceramics sintered at 830 °C shows ferroelectric polarization (2Pr) 7.3723 μC/cm2 at an applied field of 15 kV/cm but the BSFO ceramics sintered at 850 °C shows no ferroelectric polarization at room temperature. The presence of magnetization and reasonable ferroelectric polarization at room temperature in BSFO ceramics sintered at 830 °C make this material suitable for multiferroic application.

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.

Effect of Sr-doping on multiferroic properties of Bi0.8La0.2Fe0.9Mn0.1O3

The effect of Sr-doping on ferroelectricity and ferromagnetism at room temperature has been studied for Bi0.8La0.2Fe0.9Mn0.1O3 ceramic system. X-ray diffraction shows that a structural phase transition occurs from rhombohedral structure of BiFeO3 (space group R3c) to orthorhombic structure of Bi0.8La0.2FeO3 (space group C222). Substitutions of Sr-ions in Bi-site and Mn-ions in Fe-site do not induce any further structural change. Moreover, doping of Sr-ions plays a crucial role to obtain single phased samples. DTA and TGA studies show that both the magnetic transition temperature (TM) and the ferroelectric transition temperature (TC) decrease for Bi0.7Sr0.1La0.2Fe0.9Mn0.1O3. Sr-doping enhances the ferroelectric property by increasing the electric polarization. M–H measurement shows that Sr-ions partially destroy the spin cycloidal structure in it giving rise to weak ferromagnetism (nonlinearity) at room temperature.

Effect of annealing temperature on multiferroic properties of Bi0.85Nd0.15FeO3 thin films prepared by sol-gel method

Bi0.85Nd0.15FeO3 films were prepared on Pt/Ti/SiO2/Si substrate by a sol-gel method, and annealed at different temperatures. The effect of annealing temperature on the crystal structure, dielectric, ferroelectric, and ferromagnetic properties was investigated. When the Bi0.85Nd0.15FeO3 films were annealed at 490−600°C, the single phase was obtained. Bi0.85Nd0.15FeO3 film annealed at 600°C showed good multiferroic properties with ɛr of 145 (at 1 MHz), Ms of 44.8 emu/cm3, and 2Pr of 16.6 μC/cm2.

Multiferroic properties of Bi0.9Gd0.1Fe0.9Mn0.1O3 thin film

Monolithic oxides whose lattice structures exhibit both ferroelectric and magnetic ordering and eventually intrinsic coupling between them are known as multiferroics. The possibility to switch magnetization by an electric field and reciprocally polarization by a magnetic field may allow new applications spanning the fields from new memory devices to medical measuring technology. Until now, the only monolithic oxide that has been shown to exhibit both (weak) magnetism and ferroelectric polarization at room temperature is BiFeO3 (BFO). However, as this material is a line compound, i.e., with sharply defined stoichiometry, its properties largely depend on defects and parasitic phases that could arise during processing. In the present work, we report on a new compound based on the solid solution GdMnO3–BiFeO3 (GdMBFO) that exhibit a fairly high magnetization coupled with moderate ferroelectric polarization at room temperature. Using conductive-tip atomic force microscopy, we show the highly electrically homogeneous microstructure. Ferroelectric polarization switching is obtained both as P-E hysteresis (or I-E) and capacitance-voltage butterfly curves. The effects of space charge on ferroelectric polarization that often bias polarization measurements reported for pure BFO are shown to be marginal. The high magnetization obtained for GdMBFO has allowed us to determine the Néel temperature (TN) directly from magnetic measurements. This results bears novelty as it is the first time that TN is reported for BFO-base thin films. The origin of magnetization improvement is discussed in terms of Gd substitution effects on octahedral distortion and tilting.

Multiferroic properties of Bi0.87La0.05Tb0.08FeO3 ceramics prepared by spark plasma sintering

Dense Bi0.87La0.05Tb0.08FeO3 ceramics were prepared by spark plasma sintering. The sample showed stable dielectric constant and low dielectric loss (∼5%), and a saturation ferroelectric loop with remnant polarization of 17μC∕cm2 and saturation polarization of 19μC∕cm2, as well as good ferromagnetism with saturation magnetization of 0.71emu∕g, at room temperature. After the sample was poled, its piezoelectric constant was measured as 12.8pC∕N, and, in particular, an obvious magnetoelectric coupling was observed.