Search Results (40)

Lead ferrite (Pb₂Fe₂O₅) is a promising multiferroic material that exhibits both ferroelectric and magnetic properties at room temperature. This study investigates how substituting niobium and adjusting the synthesis temperature affect the structural, morphological, and ferroelectric properties of lead ferrite thin films deposited via reactive magnetron sputtering. Niobium-substituted PFO films (Pb₂Fe_2(1−x)Nb_2xO₅), where x corresponds to Nb₂O₅ contents of 3 wt.%, 5 wt.% and 10 wt.%, were prepared for this study, and denoted as PFONb3, PFONb5 and PFONb10, respectively. X-ray diffraction analysis confirmed the formation of Nb-substituted PFO phases, while polarization–electric field measurements demonstrated an increase in remnant polarization (P_r), with higher Nb content reaching a maximum P_r of 65 µC/cm² at 10 wt.% Nb and a substrate temperature of 500 °C. Scanning electron microscopy and energy-dispersive spectroscopy revealed a uniform distribution of elements and a well-defined surface structure. These results highlight the need to fine tune synthesis parameters, such as temperature and substitution concentrations, to achieve optimal ferroelectric characteristics. Full article

In this work, three composite materials based on Terfenol-D and PZT-type material were obtained with a classic sintering method using a combination of 0–3 phases, where the ferroelectric phase was doped PZT material (P) and the magnetic phase was Terfenol-D (T). The percentage of P and T components in the composites was variable, i.e., 90% P/10% T (P90-T10), 70% P/30% T (P70-T30), and 50% P/50% T (P50-T50). Structural, microstructure, dielectric, and magnetic properties and DC electric conductivity of multiferroic composites were investigated. Chemical composition analyses and X-ray studies showed a decomposition of the composite compositions, forming additional phases, most of which contained rare earth elements and Fe. Microstructural SEM-BE (backscattering) images distinguished areas of bright intensity with a dominant ferroelectric phase and dark areas with a dominant magnetic element dominance. Despite the composition decomposition, the composite materials retained good dielectric and magnetic properties at room temperature. The highest stability of dielectric parameters was maintained by the P90-T10 composition with high values of permittivity ε = 570 at room temperature RT (ε_m = 7300 at the phase transition temperature T_m) and the lowest dielectric tangent loss (tanδ of 0.32 and 1.94 for RT and T_m, respectively). Increasing the Terfenol-D share in the composite causes a significant increase in dielectric tangent loss and electrical conductivity, a decrease in permittivity, and an increase in the degree of phase transition blurring. The magnetic properties for all P-T composite compositions at RT were preserved and were 0.31 emu/g, 1.60 emu/g, and 4.56 emu/g for P90-T10, P70-T30, P50-T50, respectively. For the M-H hysteresis loop at room temperature, the maximum magnetization increased from 1.17 emu/g for (P90-T10) to 15.18 emu/g for (P50-T50), while the coercive field decreased from 271.8 mT for P90-T10 to 9.7 mT for P50-T50. It is also interesting to maintain the high saturation of the M-H magnetic hysteresis loop in the composite with the lowest Terfenol-D content (P90-T10). The magnetic properties for all P-T composite compositions at room temperature were preserved and were 0.31 emu/g, 1.60 emu/g, and 4.56 emu/g for P90-T10, P70-T30, and P50-T50, respectively. For the M-H hysteresis loop at RT, the maximum magnetization increased from 1.17 emu/g for (P90-T10) to 15.18 emu/g for (P50-T50), while the coercive field decreased from 0.272 T for P90-T10 to 0.001 T for P50-T50. It is also interesting to maintain the high saturation of the M-H magnetic hysteresis loop in the composite with the lowest Terfenol-D content (P90-T10). Due to the tendency to combine with oxygen and the high electric conductivity of Terfenol-D, limiting its amount in the composite composition is appropriate. At 10% of Terfenol-D, the composite has good dielectric properties, and the magnetic parameters remain satisfactory. Full article

Laser ablation was used to successfully fabricate multiferroic bilayer thin films, composed of BaTiO₃ (BTO) and CoFe₂O₄ (CFO), on highly doped (100) Si substrates. This study investigates the influence of BaTiO₃ layer thickness (50–220 nm) on the films’ structural, magnetic, and dielectric properties. The dense, polycrystalline films exhibited a tetragonal BaTiO₃ phase and a cubic spinel CoFe₂O₄ layer. Structural analysis revealed compression of the CoFe₂O₄ unit cell along the growth direction, while the BaTiO₃ layer showed a tetragonal distortion, more pronounced in thinner BTO layers. These strain effects, attributed to the mechanical interaction between both layers, induced strain-dependent wasp-waisted behavior in the films’ magnetic hysteresis cycles. The strain effects gradually relaxed with increasing BaTiO₃ thickness. Raman spectroscopy and second harmonic generation studies confirmed BTO’s non-centrosymmetric ferroelectric structure at room temperature. The displayed dielectric permittivity dispersion was modeled using the Havriliak–Negami function combined with a conductivity term. This analysis yielded relaxation times, DC conductivities, and activation energies. The observed BTO relaxation time behavior, indicative of small-polaron transport, changed significantly at the BTO ferroelectric Curie temperature (Tc), presenting activation energies E_τ in the 0.1–0.3 eV range for T < Tc and E_τ > 0.3 eV for T > Tc. The BTO thickness-dependent Tc behavior exhibited critical exponents ν ~ 0.82 consistent with the 3D random Ising universality class, suggesting local disorder and inhomogeneities in the films. This was attributed to the composite structure of BTO grains, comprising an inner bulk-like structure, a gradient strained layer, and a disordered surface layer. DC conductivity analysis indicated that CoFe₂O₄ conduction primarily occurred through hopping in octahedral sites. These findings provide crucial insights into the dynamic dielectric behavior of multiferroic bilayer thin films at the nanoscale, enhancing their potential for application in emerging Si electronics-compatible magneto-electric technologies. Full article

Using a microscopic model and Green’s function theory, we have investigated the co-doping effect on ferroelectric KNbO₃ nanoparticles. Let us emphasize that while the doping with transition metal ions at the Nb site leads an increase in the ferromagnetism and a reduction the band gap, it also decreases the ferroelectricity. On the other hand, doping with La or Ba at the K site leads to enhanced polarization, but does not lead to the appearance of ferromagnetism and reduction in the band gap. Therefore, we have studied co-doping with La/Cr and La/Co ions, which leads to increasing the magnetization and polarization as well as to strongly decreasing the band gap energy. Thus, we observe a multiferroic material with room-temperature ferromagnetism and ferroelectricity as well as small band gap energy which can be tuned using various co-doping ions. There is a good agreement with the existing experimental data. Full article

Bismuth ferrite (BiFeO₃, BFO) is one of the few single-phase crystalline compounds exhibiting strong multiferroic properties at room temperature, which makes it promising for use in various fields of science and technology. The remarkable characteristics of BFO at the nanoscale position it as a compelling candidate for enhancing the functionalities of polymeric nanocomposite materials. In this study, we explore the fabrication of polyvinylidene fluoride (PVDF) nanocomposites with a variable content of BFO nanopowders (0, 5, 10, 15, 20, and 25 wt%) by solution casting in the form of thin films with the thickness of ~60 µm. Our findings reveal that the presence of BFO nanoparticles slightly facilitates the formation of β- and γ-phases of PVDF, known for their enhanced piezoelectric properties, thereby potentially expanding the utility of PVDF-based materials in sensors, actuators, and energy harvesting devices. On the other hand, the increase in filler concentration leads to enlarged spherulite diameter and porosity of PVDF, as well as an increase in filler content above 20 wt% resulting in a decrease in the degree of crystallinity. The structural changes in the surface were found to increase the hydrophobicity of the nanocomposite surface. Magnetometry indicates that the magnetic properties of nanocomposite are influenced by the BFO nanoparticle content with the saturation magnetization at ~295 K ranging from ~0.08 emu/g to ~0.8 emu/g for samples with the lowest and higher BFO content, respectively. Full article

This investigation is motivated by an interest in multiferroic BaFe₁₂O₁₉ (BFO), which combines advanced ferrimagnetic and ferroelectric properties at room temperature and exhibits interesting magnetoelectric phenomena. The ferroelectric charge storage properties of BFO are limited due to high coercivity, low dielectric constant, and high dielectric losses. We report the pseudocapacitive behavior of BFO, which allows superior charge storage compared to the ferroelectric charge storage mechanism. The BFO electrodes show a remarkably high capacitance of 1.34 F cm⁻² in a neutral Na₂SO₄ electrolyte. The charging mechanism is discussed. The capacitive behavior is linked to the beneficial effect of high-energy ball milling (HEBM) and the use of an efficient dispersant, which facilitates charge transfer. Another approach is based on the use of conductive polypyrrole (PPy) for the fabrication of PPy-BFO composites. The choice of new polyaromatic dopants with a high charge-to-mass ratio plays a crucial role in achieving a high capacitance of 4.66 F cm⁻² for pure PPy electrodes. The composite PPy-BFO (50/50) electrodes show a capacitance of 3.39 F cm⁻², low impedance, reduced charge transfer resistance, enhanced capacitance retention at fast charging rates, and good cyclic stability due to the beneficial effect of advanced dopants, HEBM, and synergy of the contribution of PPy and BFO. Full article

The purpose of the present study was to learn the morphological, structural, ferroelectric, dielectric, electromechanical, magnetoelectric, and magnetic properties, and DC conductivity of BaTiO₃-Ni_0.64Zn_0.36Fe₂O₄ (BT-F) multiferroic composites compacted via the free sintering method. The influence of the ferrite content in ceramic composite materials on the functional properties is investigated and discussed. X-ray diffraction studies confirmed the presence of two main phases of the composite, with strong reflections originating from BaTiO₃ and weak peaks originating from nickel-zinc ferrite. BT-F ceramic composites have been shown to exhibit multiferroism at room temperature. All studied compositions have high permittivity values and low dielectric loss, while the ferroelectric properties of the BT component are maintained at a high level. On the other hand, magnetic properties depend on the amount of the ferrite phase and are the strongest for the composition with 15 wt.% of F (magnetization at RT is 4.12 emu/g). The magnetoelectric coupling between BT and F phases confirmed by the lock-in technique is the largest for 15 wt.% ferrite. In the present work, the process conditions of the free sintering method for obtaining BT-F multiferroic composite with good electrical and magnetic properties (in one material) were optimized. An improved set of multifunctional properties allows the expansion of the possibilities of using multiferroic composites in microelectronics. Full article

The magnetization mechanism of Co-doped BaTiO₃ ultrathin films is a subject of debate, which results in difficulties with the design of new multiferroics based on BaTiO₃ matrixes. With the aid of a first-principles approach, it was observed that when the interstitial site and Ti vacancy were filled with Co, the configuration behaved in a nonmagnetic manner, indicating the significance of the Co content. Moreover, in the case of Co substituting two neighboring Ti atoms, when a direct current field was applied in the [100] direction, the magnetic domains excluding those in the [100], [010], and [001] directions were directed away. Further, the magnetoelectric constant was evaluated at ~449.3 mV/cmOe, showing strong magnetoelectric coupling at room temperature. Clearly, our study indicates that strict control of Ba, Ti, O, and Co stoichiometry can induce an electric and magnetic field conversion in two-dimensional BaTiO₃ and may provide a new candidate for single-phase multiferroics for application in next-generation multifunctional devices. Full article

Multiferroic materials capable of robust magnetoelectric coupling at room temperature are currently being explored for their possible multifunctional device applications. Highly (100)-oriented Pb(Fe_0.5Ta_0.5)_x(Zr_0.53Ti_0.47)_1−x (PZTFT_x) thin films (x = 0.2 and 0.3) with a thickness of about 300 nm were grown on La_0.67Sr_0.33CoO₃ (LSCO)-buffered MgO 100-oriented substrates via the pulsed laser deposition method. An analysis of their X-ray diffraction patterns suggests the stabilization of the orthorhombic phase in the thin films at room temperature. Dielectric spectroscopic measurements of the metal–insulator–metal (Pt/PZTFT_x/LSCO) thin-film capacitors as a function of temperature revealed a diffuse ferroelectric-to-paraelectric phase transition around Tm ~520 and 560 K for the x = 0.2 and 0.3 thin films, respectively. Well-saturated electrical hysteresis loops with large remanent (Pr) and saturation (Ps) polarizations were observed in these capacitors, which indicates the establishment of intrinsic ferroelectric ordering in the thin films at room temperature. These thin films retained ferromagnetic/ferrimagnetic ordering up to 300 K and showed saturation magnetization values of 8.3 (x = 0.2) and 6.1 (x = 0.3) emu/cm³ at room temperature. The magnetoelectric coupling constants of 2040 mV/cmOe (x = 0.2) and 850 mV/cmOe (x = 0.3), respectively, were obtained at an in-plane bias field at room temperature. The present study demonstrates that PZTFT_x thin films are multiferroic at room temperature with large magnetoelectric couplings, and these materials may be suitable for use in magnetic sensors and spintronic device applications. Full article

Compounds and solid solutions of bismuth ferrite (BiFeO₃)—barium titanate (BaTiO₃) system are of great scientific and engineering interest as multiferroic and potential high-temperature lead-free piezoelectric materials. In the present paper, the results of research on the synthesis and characterisation of 0.67Bi₁.₀₂FeO₃–0.33BaTiO₃ (67BFBT) ceramics in terms of crystal structure and dielectric and piezoelectric properties are reported. It was found that the produced 67BFBT ceramics were characterised by a tetragonal crystal structure described by the P4mm space group, an average crystallite size <D> ≈ 80 nm, and an average strain <ε> = 0.01%. Broad-band dielectric spectroscopy (BBDS) was employed to characterise the dielectric response of polycrystalline ceramics. The frequency range from ν = 10⁻¹ Hz to ν = 10⁵ Hz was used to characterise the influence of the electric field strength on dielectric response of the ceramic sample at room temperature. The dielectric spectra were checked for consistency with the Kramers–Kronig test, and the high quality of the measurements were confirmed. The electric equivalent circuit method was used to fit the dielectric spectra within the frequency range that corresponded to the occurrence of the resonant spectra of the radial mode for thin disk sample, i.e., from ν = 10⁵ Hz to ν = 10⁷ Hz and the temperature range from T = −20 °C to T = 50 °C. The electric equivalent circuit [R_sCPE₁([L₁R₁C₁]C₀)] was used, and good fitting quality was reached. The relevant calculations were performed, and it was found that the piezoelectric charge coefficient exhibited a value of d₃₁ = 35 pC/N and the planar coupling factor was k_p = 31% at room temperature. Analysis of impedance spectra performed in terms of circumferential magnetic field made it possible to establish an influence of magnetic field on piezoelectric parameters of 67BFBT multiferroic ceramics. Additionally, the “magnetic” tunability of the modulus of the complex dielectric permittivity makes 67BFBT a sensing material with vast potential. Full article

This work presents the electrophysical properties of the multiferroic ceramic composites obtained as a result of combining both magnetic and ferroelectric material. The ferroelectric components of the composite are materials with the following chemical formulas: PbFe_0.5Nb_0.5O₃ (PFN), Pb(Fe_0.495Nb_0.495Mn_0.01)O₃ (PFNM₁), and Pb(Fe_0.49Nb_0.49Mn_0.02)O₃ (PFNM₂), while the magnetic component of the composite is the nickel-zinc ferrite (Ni_0.64Zn_0.36Fe₂O₄ marked as F). The crystal structure, microstructure, DC electric conductivity, and ferroelectric, dielectric, magnetic, and piezoelectric properties of the multiferroic composites are performed. The conducted tests confirm that the composite samples have good dielectric and magnetic properties at room temperature. Multiferroic ceramic composites have a two-phase crystal structure (ferroelectric from a tetragonal system and magnetic from a spinel structure) without a foreign phase. Composites with an admixture of manganese have a better set of functional parameters. The manganese admixture increases the microstructure’s homogeneity, improves the magnetic properties, and reduces the electrical conductivity of composite samples. On the other hand, in the case of electric permittivity, a decrease in the maximum values of ε_m is observed with an increase in the amount of manganese in the ferroelectric component of composite compositions. However, the dielectric dispersion at high temperatures (associated with high conductivity) disappears. Full article

The potential application of multiferroic materials in new electronic devices attracts more and more attention from people either in an academic field or industry. This paper reports that M-type lanthanum-doped barium ferrite (La_0.75Ba_0.25Fe₁₂O₁₉) demonstrates full antiferroelectric (AFE) and excellent magnetoelectric coupling effects at room temperature, while its AFE phase displays a zero macroscopic net polarization. The dramatic change in the dielectric constant near the Curie temperature far below room temperature represents the transition from ferroelectrics (FE) to antiferroelectrics. The fully separated double electric polarization hysteresis (P–E) loops confirmed its AFE performance. Its E_F and E_A are located at 1100 kV/cm and 850 kV/cm, respectively. The large M–H loop showed a strong magnetic property simultaneously. The UV-Vis-NIR optical spectrum revealed that La_0.75Ba_0.25Fe₁₂O₁₉ is also a semiconductor, whose direct bandgap energy (E_g) was determined to be 1.753 eV. Meanwhile, La_0.75Ba_0.25Fe₁₂O₁₉ showed strong ME coupling and a GMR effect. A 1.1 T magnetic field reduced its resistance by 110% at 30 kHz. The multiple functions combined in one phase would create new options for high energy storage capacitors, microactuators, pyroelectric safety sensors, cooling devices, and pulsed power generators and so on, as well as great opportunities for generating new electronic devices with active magnetoelectric coupling effects. Full article

Multiferroic thin films are a promising class of multifunctional materials, since they allow the integration of multiple functionalities within a single device. In order to overcome the scarcity of single phase multiferroics, it is crucial to develop novel multiferroic heterostructures, combining good ferroelectric and ferromagnetic properties as well as a strong coupling between them. For this purpose, Ba₂EuFeNb₄O₁₅/BaFe₁₂O₁₉ multiferroic magnetoelectric bilayers have been epitaxially grown on niobium doped SrTiO₃ (100) single crystal substrates by pulsed laser deposition. The simultaneous presence of both ferroelectric and magnetic properties—due, respectively, to the Ba₂EuFeNb₄O₁₅ and BaFe₁₂O₁₉ components—was demonstrated at room temperature, attesting the multiferroic nature of the heterostructure. More interestingly, a strong magnetoelectric coupling was demonstrated (i) by manipulating the ferroelectric properties via an external magnetic field, and conversely, (ii) by tuning the magnetic properties via an external electric field. This strong magnetoelectric coupling shows the high interdependence of both ferroic orders in the Ba₂EuFeNb₄O₁₅/BaFe₁₂O₁₉ heterostructure, mediated by elastic (epitaxial) strain at the interfaces. Full article

The appearance of antiferroelectrics (AFE) in the ferrimagnetism (FM) system would give birth to a new type of multiferroic candidate, which is significant to the development of novel devices for energy storage. Here we demonstrate the realization of full antiferroelectrics in a magnetic La_0.5Sr_0.5Fe₁₂O₁₉ system (AFE+FM), which also presents a strong magnetodielectric response (MD) and magnetoresistance (MR) effect. The antiferroelectric phase was achieved at room temperature by replacing 0.5 Sr²⁺ ions with 0.5 La²⁺ ions in the SrFe₁₂O₁₉ compound, whose phase transition temperature of ferroelectrics (FE) to antiferroelectrics was brought down from 174 °C to −141 °C, while the temperature of antiferroelectrics converting to paraelectrics (PE) shifts from 490 °C to 234 °C after the substitution. The fully separated double P-E hysteresis loops reveal the antiferroelectrics in La_0.5Sr_0.5Fe₁₂O₁₉ ceramics. The magnitude of exerting magnetic field enables us to control the generation of spin current, which induces MD and MR effects. A 1.1T magnetic field induces a large spin current of 15.6 n A in La_0.5Sr_0.5Fe₁₂O₁₉ ceramics, lifts up dielectric constants by 540%, and lowers the resistance by −89%. The magnetic performance remains as usual. The multiple functions in one single phase allow us to develop novel intelligent devices. Full article

This paper will provide a brief overview of the unique multiferroic material Bismuth ferrite (BFO). Considering that Bismuth ferrite is a unique material which possesses both ferroelectric and magnetic properties at room temperature, the uniqueness of Bismuth ferrite material will be discussed. Fundamental properties of the material including electrical and ferromagnetic properties also will be mentioned in this paper. Electrical properties include characterization of basic parameters considering the electrical resistivity and leakage current. Ferromagnetic properties involve the description of magnetic hysteresis characterization. Bismuth ferrite can be fabricated in a different form. The common forms will be mentioned and include powder, thin films and nanostructures. The most popular method of producing thin films based on BFO materials will be described and compared. Finally, the perspectives and potential applications of the material will be highlighted. Full article