FeO3 Multiferroics Research Articles

Structural, dielectric and magnetic characteristics of Mn-substituted Bi0.80Nd0.20FeO3 multiferroics

Structural, dielectric and magnetic characteristics of Mn-substituted Bi0.80Nd0.20FeO3 multiferroics

Magnetic contributions in multiferroic gadolinium modified bismuth ferrite ceramics

Bi0.88Gd0.12FeO3 multiferroics are of interest for next-generation electronics and are shown with a remnant magnetization 0.2 emu·g−1, coercive field 8 kOe, Curie temperature 370 °C and magnetization of 0.7 emu·g−1 at magnetic fields 30 kOe. Scanning probe microscopy confirmed the intrinsic multiferroicity in the perovskite phase with coexistence of ferroelectric/ferroelastic and ferromagnetic domain structures. Strong magnetic hysteresis was produced by thermal cycling to 1000 °C due to degeneration of the perovskite phase into iron oxide inclusions, highlighting the importance of processing, thermal history and thermodynamic stability for minimizing the amount of parasitic magnetic secondary phases.

Specific Heat and the Dielectric Properties of Bi0.8Ho0.2FeO3 Multiferroic

The specific heat and the dielectric permittivity of Bi0.8Ho0.2FeO3 multiferroics have been studied in the wide temperature range 300–750 K. The doping with rare-earth element holmium is found to lead to substantial changes in the temperature dependences of specific heat Cp and dielectric permittivity e' at high temperatures. The additional contribution to the specific heat is shown can be interpreted as a Schottky anomaly for three-level states which form due to a distortion of the lattice parameters as a result of doping. Additional anomaly characteristic of a phase transition is observed in temperature dependences of Cp and e'. The results are discussed in combination with the data of structural studies.

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The heat capacity and permittivity of Bi0.8Ho0.2FeO3 multiferroics were studied in a wide temperature range of 300--750 K. It was found that doping with holmium with rare-earth element leads to significant changes in the temperature dependences of the specific heat Cp and permittivity ε 'at high temperatures. It is shown that an additional contribution to the specific heat can be interpreted as a Schottky anomaly for three-level states arising due to distortion of the lattice parameters upon doping. An additional anomaly characteristic of the phase transition was found in the temperature dependences of Cp and ε '. Research results are discussed in conjunction with structural studies.

Structural transition, electrical and magnetic properties of Cr doped Bi0.9Sm0.1FeO3 multiferroics

The structural, vibrational, electrical and magnetic properties of Bi0.9Sm0.1Fe1-xCrxO3 (0.02 ≤ x ≤ 0.1) ceramics have been investigated in the vicinity of the morphotropic phase boundary (MPB) between the rhombohedral and orthorhombic structures. X-ray diffraction (XRD) patterns reveal a gradual formation of the orthorhombic phase and Bi14CrO24 impurity with increasing chromium concentration. The Rietveld refinement and Raman scattering analysis confirm the structural transformation from the polar R3c to the anti-polar Pnam phases. The Cole-Cole plots show two relaxation regimes which are attributed to gain and grain boundary responses above room temperature. The slim magnetic hysteresis loops are observed in samples with x = 0.02–0.08, while a robust loop with the coercivity field of Hc ≈ 1200 Oe is observed for x = 0.1 sample where the canted antiferromagnetic phase is significantly contributed to the total magnetization. This result approves that the cycloidal spin structure cannot be suppressed by Cr doping.

Evolution of structure and magnetic properties in Eu Bi1−FeO3 multiferroics obtained under high pressure

Abstract The structure, microstructure, magnetic properties and magnetocaloric effect in the BiFeO3-based multiferroics with a partial isovalent substitution of bismuth for europium ions have been experimentally and theoretically investigated by X-ray diffraction, SEM and magnetic methods. The ceramic EuxBi1−xFeO3 (0 ≤ x ≤ 0.2) samples have been prepared by a solid-state reaction method under cold pressing at high pressure P = 4 GPa. With increase in the concentration of the doping Eu element a structural phase transition from a rhombohedral R3c to an orthorhombic Pn21a perovskite structure is observed. Microstructure and chemical composition of the EuxBi1−xFeO3 samples have been studied by SEM data. Temperature dependences of magnetization for the Eu-doped multiferroics demonstrate two magnetic “weak ferromagnetic-antiferromagnetic” and “antiferromagnetic-paramagnetic” phase transitions in a high temperature range T = 640–822 K. The presence of a weak ferromagnetism in all compositions is confirmed by open loops of magnetic field dependencies. On the basis of the analysis of magnetic data, magnetic entropy change, heat capacity change, relative cooling power and full-width at half-maximum of the peak have been calculated. It has been found out that the thermodynamic characteristics strongly depend on the degree of substitution, temperature, and magnitude of magnetic field.

Holmium induced structural transformation and improved dielectric and magnetic properties in Bi0.80La0.20FeO3 multiferroics

Abstract The change in structural behaviour, magnetic measurement & dielectric characteristics of polycrystalline Bi0.80−xLa0.20HoxFeO3 (x = 0.00, 0.05, 0.10 & 0.15 and designated as LH0, LH05, LH10 and LH15 respectively) multiferroics prepared using method of the solid-state reaction, have been investigated. The powder X-ray diffraction and Rietveld refinement of the XRD spectrum indicates that Bi0.80La0.20FeO3 multiferroics have single phase in R3c. Rietveld refined spectrum of the XRD conclude that holmium substitution at A-site for the samples LH05 and LH10 is crystallized as combo of rhombohedral R3c and orthorhombic Pbam space group. Holmium substitution for LH15 has changed the rhombohedral R3c symmetry of Bi0.80La0.20FeO3 to the orthorhombic Pbam symmetry. The magnetic behaviour was studied by recording magnetization with magnetic up to ±10 kOe. Weak ferromagnetic behaviour of all samples attributes that co-doping effectively concealed spiral spin configuration by altering the canting angle. Dielectric behaviour of prepared ceramic compounds was carried by impedance analyser within frequency ranged 100 Hz–7 MHz for different temperatures.

Investigation of crystal structure and improved magnetic and dielectric properties of Ti-substituted Bi0.90Ho0.10FeO3 multiferroics

Bi0.90Ho0.10Fe1−xTixO3 multiferroics (with x = 0.00, 0.05, 0.10, and 0.15) were synthesized by method of solid state reaction. The XRD, SEM, dielectric properties, and magnetic measurements of the compounds were carried out. The X-ray patterns show structural change for x = 0.15. Rietveld refinement of the XRD patterns deduces that the samples for x = 0.00, 0.05, and 0.10 are found to fit well with rhombohedral R3c symmetry, while for x = 0.15, sample accomplishes best fitting by the mixed-phase setting of rhombohedral R3c and triclinic P1 space group. The micro-Raman scattering observation also confirms the phase transformation. The change in crystal structure is attributed to the distortion of FeO6 octahedra due to replacing a part of B-site Fe ions by Ti ions. Magnetic measurements were performed at room temperature up to an external magnetic field of ± 10 kOe. Dielectric behaviour of all prepared ceramic samples was carried by impedance/gain phase analyser within the frequency range from 100 Hz to 7 MHz at different temperatures. It was observed that the Ti co-doping shows a significant role for the improving multiferroics properties.

Characterization of human liver organoids cultured on a newly developed microfluidic chip with improved hepatic functions

The change in structural behaviour, magnetic measurement & dielectric characteristics of polycrystalline Bi0.80−xLa0.20HoxFeO3 (x = 0.00, 0.05, 0.10 & 0.15 and designated as LH0, LH05, LH10 and LH15 respectively) multiferroics prepared using method of the solid-state reaction, have been investigated. The powder X-ray diffraction and Rietveld refinement of the XRD spectrum indicates that Bi0.80La0.20FeO3 multiferroics have single phase in R3c. Rietveld refined spectrum of the XRD conclude that holmium substitution at A-site for the samples LH05 and LH10 is crystallized as combo of rhombohedral R3c and orthorhombic Pbam space group. Holmium substitution for LH15 has changed the rhombohedral R3c symmetry of Bi0.80La0.20FeO3 to the orthorhombic Pbam symmetry. The magnetic behaviour was studied by recording magnetization with magnetic up to ±10 kOe. Weak ferromagnetic behaviour of all samples attributes that co-doping effectively concealed spiral spin configuration by altering the canting angle. Dielectric behaviour of prepared ceramic compounds was carried by impedance analyser within frequency ranged 100 Hz–7 MHz for different temperatures.

Sol–gel synthesis and investigation of structural, electrical and magnetic properties of Pb doped La0.1Bi0.9FeO3 multiferroics

A sol–gel based auto-combustion technique has been employed to synthesize polycrystalline La0.1Bi0.9−xPbxFeO3 (x = 0.0, 0.05, 0.10, 0.20, 0.30) ceramics. The samples have been characterized by X-ray diffraction, scanning electron microscopy, an LCR-meter and a vibrating sample magnetometer for their structural and morphological features, as well as electrical and magnetic properties, respectively. The structural analysis revealed that when Pb was doped at Bi-sites in La0.1Bi0.90FeO3, the host retained the rhombohedrally distorted perovskite structure, attributed to the non centro-symmetric space group R3c. The surface morphological studies revealed that the grain size was increased and formed agglomerates at high concentrations of Pb contents. The dielectric parameters displayed conventional ferrite behavior depicting high values at low frequencies and decreasing with rise in frequencies, leading to constant values at still higher frequencies. The magnetic properties were changed non-monotonically with increasing Pb concentration. This non-monotonical behavior with increasing Pb could be attributed to the canting of the antiferromagnetic spins in BiFeO3 based multiferroics.

Thermal diffusion and heat conductivity of BiFeO3 and Bi0.95La0.05FeO3 multiferroics at high temperatures

The thermal diffusion and heat conductivity of BiFeO3 and Bi0.95La0.05FeO3 multiferroics at high temperatures (300–1200 K) have been examined. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions have been revealed. The temperature dependence of the mean free path of phonons has been determined.

Effect of Co substitution on the structural, electrical, and magnetic properties of Bi0.9La0.1FeO3 by sol-gel synthesis

Cobalt (Co)-doped Bi0.9La0.1FeO3 multiferroics were synthesized by a sol-gel method based on the autocombustion technique. As-synthesized powder was examined using various characterization techniques to explore the effect of Co substitution on the properties of Bi0.9La0.1FeO3. X-ray diffraction reveals that Co-doped Bi0.9La0.1FeO3 preserves the perovskite-type rhombohedral structure of BiFeO3, and the composition without Co preserves the original structure of the phase; however, a second-phase Bi2Fe4O9 has been identified in all other compositions. Surface morphological studies were performed by scanning electron microscopy. Temperature-dependent resistivity of the samples reveals the characteristic insulating behavior of the multiferroic material. The resistivity is found to decrease with the increase both in temperature and Co content. Room temperature frequency-dependent dielectric measurements were also reported. Magnetic measurements show the enhancement in magnetization with the increase in Co content.

Structure and piezoelectric properties of BiFeO3 and Bi0.92Dy0.08FeO3 multiferroics at high temperature

Multiferroic BiFeO3 and Bi0.92Dy0.08FeO3 ceramics were prepared to study their crystal structures and piezoelectric properties. BiFeO3 exhibits rhombohedral phase below 810°C. Although Bi0.92Dy0.08FeO3 ceramic also shows rhombohedral phase at room temperature, it allows the coexistence of rhombohedral phase and orthorhombic phase at 460–650°C. Both samples have maximum polarizations of >21μC/cm2 and piezoelectric d33 values of ∼37pC/N at room temperature. Their polarized slices show the dielectric anomalies and impedance anomalies because of vibrating resonances below 500°C, and the thickness vibration electromechanical coupling factor is ∼0.6 and ∼0.4 for BiFeO3 and Bi0.92Dy0.08FeO3, respectively. The vibrating resonances confirm piezoelectric responses. Furthermore, samples' impedance and resistance decrease fast with temperature increasing, which screens piezoelectric response above 550°C.

Structural transformation and improved dielectric and magnetic properties in Ti-substituted Bi0.8La0.2FeO3 multiferroics

Ti-substituted BiLaFeO3 ceramics having compositions Bi0.8La0.2Fe1−xTixO3 (x = 0.0, 0.05, 0.1, 0.15) were synthesized by the conventional solid-state reaction method. Powder x-ray diffraction investigations performed at room temperature show that the crystal structure is rhombohedral for x = 0.0, 0.05; tetragonal for x = 0.15; and a phase boundary occurs at x = 0.1. In the Rietveld refinement good agreement between the observed and calculated pattern was observed. Dielectric response of these samples was analysed in the frequency range 1 kHz–5 MHz at different temperatures. A decrease in the values of real (ε′) and imaginary (ε″) parts of dielectric constant with Ti substitution indicates reduced conductivity and hence enhanced resistivity in doped samples. Stability of dielectric constant and conductivity with temperature is considerably improved with Ti substitution. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic properties of Bi0.8La0.2FeO3 ceramics are considerably improved on Ti substitution along with a significant opening in the room temperature M–H hysteresis loop. Higher values of remanent magnetization (Mr) 0.1373 and 0.1487 emu g−1; coercivity (Hc) 4.856 and 5.904 kOe are observed for samples with x = 0.1 and 0.15, respectively. This is due to the structural phase transition from rhombohedral to tetragonal.

Magnetoelectric interactions in BiFeO3, Bi0.95Nd0.05FeO3, and Bi0.95La0.05FeO3 multiferroics

The technology of ceramic BiFeO3, Bi0.95Nd0.05FeO3, and Bi0.95La0.05FeO3 multiferroics is described. The room-temperature magnetization, magnetoelectric (ME), and magnetodielectric (MDE) effects in these compounds have been studied. It is established that even a small fraction (x = 0.05) of rare-earth additives (La, Nd) to bismuth ferrite not only enhance its magnetic properties, but also significantly influence the ME and MDE effects. The dependence of the ME effect on the frequency of modulation of the alternating magnetic field in Bi0.95Nd0.05FeO3, and Bi0.95La0.05FeO3 is more pronounced than in pure BiFeO3.