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Temperature-dependent photo-response in multiferroic BiFeO 3 revealed by transmission measurements
摘要： We studied the light-induced effects in BiFeO3 single crystals as a function of temperature by means of optical spectroscopy. Here, we report the observation of several light-induced absorption features, which are discussed in terms of the photostriction effect and are interpreted in terms of excitons. The temperature dependence of their energy position suggests a possible coupling between the excitons and the lattice vibrations. Moreover, there are hints for anomalies in the temperature evolution of the excitonic features, which might be related to the temperature-induced magnetic phase transitions in BiFeO3. Our findings suggest a coupling between light-induced excitons and the lattice and spin degrees of freedom, which might be relevant for the observed ultrafast photostriction effect in multiferroic BiFeO3.
关键词： multiferroic,excitons,optical spectroscopy,BiFeO3,photostriction
更新于2025-11-25 10:30:42
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Multi-doped bismuth ferrite thin films with enhanced multiferroic properties
摘要： Thin films of multi-doped bismuth ferrite, Bi0.97?xLaxSr0.03Fe0.94Mn0.04Co0.02O3 (BLxSFMC, x = 0.00–0.18), are synthesized on a fluorine-doped tin oxide (FTO)/glass substrate. The structure and multiferroic properties of the film samples are characterized and tested. The results indicate that on doping, the structure of the BLxSFMC film changes has been changed. The concentrations of both oxygen vacancies and Fe2+ are decreased. The BL0.18SFMC thin film exhibits Ohmic conduction, which reduces the influence of the built-in electric field Ebi of the space-charge region at the interface between an Au electrode and the BLxSFMC during polarization. The BL0.18SFMC thin film also exhibits enhanced ferroelectric properties than the undoped film, with a higher residual polarization of 188 μC/cm2 and a higher squareness ratio of 1.21. Meanwhile, the reduced number of oxygen vacancies also reduces the Fe2+/Fe3+ ratio, thereby enhancing the Dzyaloshinskii–Moriya interaction of Fe–O–Fe bonds, and so the BL0.18SFMC thin film exhibits enhanced ferromagnetism, with a saturation magnetization of Ms ≈ 3.94 emu/cm3. Thus, multi-ion doping can improve both the ferroelectric and ferromagnetic properties of BLxSFMC thin films.
关键词： Ohmic conduction,built-in electric field,oxygen vacancy,multiferroic
更新于2025-11-14 17:28:48
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Bandgap engineering of cobalt-doped bismuth ferrite nanoparticles for photovoltaic applications
摘要： The bandgap energy range of multiferroic bismuth ferrite is 2.2–2.7 eV, making it a promising candidate for photovoltaic (PV) applications. But its ef?ciency is still very low (<2%). This report thus focusses on the application of bismuth ferrite (BFO) engineered with cobalt (Co) doping and on the tuning of its bandgap energy (Eg). BiFeO3 is a unique multiferroic material that simultaneously displays both ferromagnetic and ferroelectric properties at room temperature. Co doped with pure BiFeO3 (BiFe(1?x)Cox O3; x = 0, 0.05, 0.1 and 0.15) was synthesized by the sol–gel method and annealed at 600?C. X-ray diffraction shows the well-arranged crystalline structure and peaks of pure and doped-BiFeO3 nanoparticles. A suitable reduction of Eg has been observed for Co-doped BiFeO3, which may be appropriate for the effective use in PV solar cells. Thermogravimetric analysis and differential scanning calorimetry were used to investigate the thermal decomposition character of the xerogel powder and the pattern of pure and doped BiFeO3 phases. Field emission scanning electron microscopy images show the surface crystallography of pure and Co-doped BiFeO3. Co-doped BiFeO3 has considerably reduced the crystallite and particle size of the samples. We have calculated the Eg of pure and doped BiFeO3 using a UV–Vis–NIR spectrophotometer and the results show the important reduction of Eg (1.60 eV) of the Co-doped samples, which may have potential applications in PV solar cells.
关键词： sol–gel,photovoltaic cells,Bandgap,nanoparticles,multiferroic
更新于2025-10-22 19:40:53
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Complex Dielectric and Impedance Spectroscopic Studies in a Multiferroic Composite of Bi2Fe4O9-BiFeO3
摘要： Complex dielectric and impedance spectroscopic studies have been carried out in a detailed manner on the system comprising of Bi2Fe4O9-BiFeO3 composite particles dispersed in a α-Fe2O3 matrix as prepared using ball milling and controlled annealing treatments. This multiferroic composite is observed to exhibit a giant dielectric constant associated with a low tangent loss. A non-Debye type of relaxation has been deduced based on complex modulus analysis. Based on these studies, the important role played by bismuth ferrite nanoshell in the core-shell composite of Bi2Fe4O9-BiFeO3 is elucidated for the observed complex impedance spectroscopic properties of the system. Electron hopping across Fe2+/Fe3+ and oxygen vacancies are deduced to be playing an important role in conduction mechanisms based on activation energy analysis of the complex impedance spectroscopy results.
关键词： dielectric,composite,Bi2Fe4O9,multiferroic
更新于2025-09-23 15:23:52
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Néel transition in the multiferroic BiFeO <sub/>3</sub> -0.25PbTiO <sub/>3</sub> nanoparticles with anomalous size effect
摘要： The role of size reduction on the structural parameters, antiferromagnetic transition temperature (TN), and spin reorientation transition temperature of BiFeO3-0.25PbTiO3 (BF-0.25PT) has been studied. Rietveld analysis using high resolution synchrotron x-ray powder diffraction data confirms that the space group of BF-0.25PT solid solutions is monoclinic Cc and not rhombohedral R3c for both bulk and nanocrystalline powders. This settles a longstanding controversy about the structure of these solid solutions toward the BiFeO3 rich end of the morphotropic phase boundary in the BiFeO3-xPbTiO3 system. Using magnetization and neutron powder diffraction data, we show that the Néel transition temperature (TN) of BF-0.25PT increases from 445 K for bulk to 480 K for 150 nm particle size. This is in marked contrast to the scaling theories of phase transitions in finite size systems. We also show that the spin reorientation transition occurring below TN in bulk monoclinic compositions like BF-0.25PT is suppressed in the nanocrystalline samples of ～150 nm particle size. Based on Rietveld refined structural parameters, we show that the asymmetry and non-linearity of the Fe-O-Fe superexchange pathways grow with decreasing particle size and that they exhibit a strong correlation with TN. We believe that the substantially enhanced Dzyaloshinskii-Moriya interaction with decreasing particle size as a result of asymmetric and non-collinear Fe-O-Fe superexchange pathways may be the key factor in raising the TN on decreasing the particle size. These observations present a new facet of type-I multiferroic materials, where superexchange pathways are intimately dependent on the ferroelectric distortion.
关键词： multiferroic,antiferromagnetic transition,BiFeO3-PbTiO3,size effect,Dzyaloshinskii-Moriya interaction,Néel transition,nanoparticles
更新于2025-09-23 15:23:52
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Structure and multiferroic properties of ternary (1?x)(0.8BiFeO3-0.2BaTiO3)-xK0.5Na0.5NbO3 (0?≤?x?≤?0.5) solid solutions
摘要： The ternary (1?x)(0.8BiFeO3-0.2BaTiO3)-xK0.5Na0.5NbO3 (0 ≤ x ≤ 0.5) solid solutions have been successfully synthesized by a solid-state reaction route. X-ray diffraction and Rietveld refinement studies reveal the phase transition from the rhombohedral and tetragonal phases to the single tetragonal phase with x increasing. The average grain size decreases initially and then increases as x increases, whereas the remnant magnetization shows an opposite trend and reaches the maximum value of ~2.09 emu/g at x = 0.3. An enhanced remnant polarization of ~8.6 μC/cm2 appears at x = 0.3 due to the structure distortion and the decrement of defects. Moreover, the remanent polarization and the relative permittivity reach the maximum value of ~20.14 μC/cm2 (10 Hz) and ~644 (1 kHz) at x = 0.5, respectively, and the corresponding dielectric loss decreases to the lowest value of ~0.022 (1 kHz). These results indicate that the properties of ternary BFO-BTO-KNN solid solutions can be modulated by adjusting the K0.5Na0.5NbO3 content to adapt to different application needs.
关键词： Microstructure,Dielectric loss,Phase transition,Multiferroic properties
更新于2025-09-23 15:22:29
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Comparative study of structural, magnetic and dielectric properties of CoFe2O4 @ BiFeO3 and BiFeO3@ CoFe2O4 core-shell nanocomposites
摘要： Nano-sized CoFe2O4 (CFO), BiFeO3 (BFO) and their core-shell composites BFO@CFO and CFO@BFO were synthesized by chemical co-precipitation method. X-ray di?raction pattern con?rmed the crystallinity and phase formation of bare CFO, BFO and their core-shell composites. Morphology and core-shell nature of these nano-particles is justi?ed by ?eld emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Magnetization curve showed the weak ferromagnetic behaviour of BFO. Typical ferrimagnetic behaviour is shown by bare CFO and core-shell nanocomposites. The value of maximum magnetization, remanence magnetization and coercivity of CFO@ BFO were found to be greater than the BFO@ CFO. Also, CFO@ BFO showed the highest value of dielectric constant in the frequency range of 104–106 Hz. Dielectric constant versus temperature curve of BFO and core-shell composites exhibit incongruity close to the anti-ferromagnetic transition temperature (370 °C) of BFO indicating presence of magnetoelectric (ME) coupling.
关键词： Multiferroic,Nanocomposite,Core-shell,Co-precipitation
更新于2025-09-23 15:21:21
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Miniature Multiferroic Interferometer for Voltage-controlled Spin-wave Logic Gates
摘要： Novel Mach-Zender-type interferometer based on thin-film multiferroic structure has been proposed and described. The performance of the main element of such device, a tunable phase shifter, has been analysed. The distinctive features of the proposed interferometer are high efficiency and small device area in comparison with other spin-wave logic gates. We expect that our results allow exploiting spin-electromagnetic wave phenomena for enhanced logic functionality and efficient data transfer.
关键词： multiferroic structure,spin-electromagnetic wave phenomena,spin-wave logic gates,Mach-Zender-type interferometer
更新于2025-09-23 15:21:01
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: <i>Ab initio</i> and Monte Carlo approaches
摘要： The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that CuCr1?xGaxO2 preserves its magnetoelectric properties up to x ≈ 0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x ≈ 0.2. Our simulations show that Ga3+ doping increases the Curie-Weiss temperature of CuCr1?xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x ≤ 0.15 through simulating P -E hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.
关键词： CuCrO2,multiferroic,Monte Carlo simulations,ferroelectric properties,magnetic properties,density functional theory,delafossite,Ga doping
更新于2025-09-23 15:21:01
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From Bulk to Nano: A comparative investigation of Structural, Ferroelectric and Magnetic properties of Sm and Ti co-doped BiFeO3 multiferroics
摘要： In this investigation, multiferroic bulk ceramic materials with nominal compositions Bi1-xSmxFe1-yTiyO3 (x, y=0.00, 0.03, 0.06) are synthesized by conventional solid-state reaction technique. Their corresponding nanoparticles are fabricated from these bulk powder materials using cost-effective ultrasonication method. Then, the structural and multiferroic properties of the synthesized nanoparticles and their bulk-counterparts are compared. The X-ray diffraction patterns of 6% Sm-Ti co-substituted BiFeO3 nanoparticles as well as their bulk powder materials confirm rhombohedral to orthorhombic structural phase transition. Dynamic Light Scattering analysis (DLS) demonstrates the formation of particles with a size in the range of 10-100 nm for the 6% Sm-Ti co-substituted BiFeO3 sample. The fabricated nanoparticles of this particular composition also exhibit suppressed leakage current density and enhanced ferroelectric behavior. These nanoparticles also demonstrate improved ferromagnetic behavior compared to their bulk counterparts. Thus, the present investigation illustrates the impact of Sm and Ti as co-doping elements with 6% concentration in BiFeO3 nanoparticles with improved structural and multiferroic properties required for practical applications.
关键词： nanoparticles,DLS analysis,leakage current density,multiferroic properties,ultrasonication
更新于2025-09-23 15:21:01