Effect of Microstrain on the Magnetic Properties of BiFeO3 Nanoparticles
TL;DR: In this article, the size induced microstrain-dependent magnetic properties of BiFeO3 nanoparticles were investigated and it was found that the micro-strain is high (e.g., 0.3%) for smaller crystallite sizes and shows a sharp decrease as the particle size increases.
Abstract: We report on size induced microstrain-dependent magnetic properties of BiFeO3 nanoparticles. The microstrain is found to be high (e > 0.3%) for smaller crystallite sizes (d < 30 nm), and shows a sharp decrease as the particle size increases. The presence of pseudo-cubic symmetry is evidenced for these nanoparticles. Raman spectral studies suggest straightening of the Fe-O-Fe bond angle accompanied by a decrease in FeO6 octahedral rotation for d < 65 nm. The magnetization shows a dip around 30 nm, half the size of spin cycloid length for BiFeO3, due to a decrease in rhombohedral distortion with crystallite size. We also observe a similar trend in the TN with respect to size indicating that the microstrain plays a significant role in controlling the magnetic property of BiFeO3.
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TL;DR: In this paper, the structure and phase identification of nanocrystalline cobalt-doped bismuth ferrites were performed using X-ray diffraction (XRD) technique and the results confirm the formation of rhombohedral-distorted Perovskite structure with R3c symmetry.
Abstract: Nanocrystalline cobalt-doped bismuth ferrites with general formula of BiFe1−δ
Co
δ
O3 (0 ≤ δ ≤ 0.1) have been synthesized using solution evaporation method. Structure and phase identification was performed with X-ray diffraction (XRD) technique. The results confirm the formation of rhombohedral-distorted Perovskite structure with R3c symmetry. A decrease in lattice parameters and an increase in X-ray density have been observed with increasing cobalt concentration in BiFeO3. Particle size determined by transmission electron microscope was in good agreement with XRD, i.e., 39 nm. Room-temperature coercivity and saturation magnetization of nanoparticles were increased up to 7.5 % of cobalt doping. Low-temperature magnetic measurements of selected sample showed increasing behavior in saturation magnetization, coercivity, effective magnetic moments, and anisotropy constant. An increase in coercivity with decrease in temperature followed theoretical model of Kneller’s law, while modified Bloch’s model was employed for saturation magnetization in temperature range of 5–300 K.
61 citations
TL;DR: In this article, the authors successfully prepared La1−xBixFeO3 nanoparticles using a solgel technique, and studied their photocatalytic, magnetic, and electrochemical properties.
50 citations
TL;DR: The results lead to the possibility of tailoring the ferroic order in multifunctional materials by means of NP size, and suggest that ferromagnetism and ferroelectricity coexist at room temperature in NPs.
Abstract: BiFeO3 (BFO) nanoparticles (NPs) were synthesized using the sol-gel method at different calcination temperatures from 400 °C to 600 °C. XRD studies have confirmed that all BFO NPs show distorted rhombohedral crystals that match the R3c space group. We found evidence of local structural strain that develops with increasing particle size as suggested by TEM and Raman spectroscopy measurements. Magnetic measurements suggest that NPs have two distinct regimes: a ferromagnetic-like one at low temperatures and a superparamagnetic-like one at room temperature. The crossover temperature increases with NPs size, suggesting a size-dependent blocking magnetic regime. Similarly, local piezoelectric measurements at room temperature in single NP have confirmed a ferroelectric order with a NP size-dependent d33 coefficient. An analysis of both the ferroelectric and the magnetic results suggest that ferromagnetism and ferroelectricity coexist at room temperature in NPs. Our results lead to the possibility of tailoring the ferroic order in multifunctional materials by means of NP size.
47 citations
TL;DR: In this article, a detailed investigation has been made on structural, magnetic, electrical, optical and photovoltaic properties of Pr doped bismuth ferrites, and a structural phase transition has been observed from (R3c) rhombohedral for pristine sample BiFeO3 to (Pnma phase) orthorhombic structure for Bi0.85Pr 0.15Fe O3 sample.
Abstract: Multiferroic Bi1−xPrxFeO3 (x = 0.0, 0.05, 0.10, 0.15, 0.20) ceramic samples have been synthesized by sol-gel method. A detailed investigation has been made on structural, magnetic, electrical, optical and photovoltaic properties of Pr doped bismuth ferrites. A structural phase transition has been observed from (R3c) rhombohedral for pristine sample BiFeO3 to (Pnma phase) orthorhombic structure for Bi0.85Pr0.15FeO3 sample. A co-existence of (R3c) rhombohedral and (Pnma) orthorhombic phases were observed for 0.05
42 citations
TL;DR: In this paper, structural and electronic properties of BiFeO3 clusters were studied using first-principles electronic structure calculations, and the role of structural modifications in developing ferromagnetic magnetism in nano-BiO3 was revealed.
Abstract: Structural and electronic properties of BiFeO3 clusters were studied using first-principles electronic structure calculations. The main aim of this work is to unveil the role of structural modifications in developing ferromagnetism in nano-BiFeO3. We have found that the ferromagnetic ground state is energetically more favorable than the antiferromagnetic ground state for this cluster. In a relaxed cluster, there are large distortions for BiO6 octahedra, comparatively small distortion but large rotation (20°) for FeO6 octahedra, and large reduction of Fe–O–Fe coupling angle (153° → 133°) compared to bulk BiFeO3. A large charge transfer from Bi-s states is predicted for cluster which may be responsible for the observed structural changes. These results are in consistent with recent experimental observation of Bi sublattice melting for small BiFeO3 nanoparticles (<18 nm). Also, a large charge transfer from Bi-s states explains why small BiFeO3 nanoparticles cannot sustain ferroelectricity. Applying a crystal...
38 citations
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TL;DR: Enhanced polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.
Abstract: Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.
5,387 citations
Abstract: Recent research activities on the linear magnetoelectric (ME) effect?induction of magnetization by an electric field or of polarization by a magnetic field?are reviewed. Beginning with a brief summary of the history of the ME effect since its prediction in 1894, the paper focuses on the present revival of the effect. Two major sources for 'large' ME effects are identified. (i) In composite materials the ME effect is generated as a product property of a magnetostrictive and a piezoelectric compound. A linear ME polarization is induced by a weak ac magnetic field oscillating in the presence of a strong dc bias field. The ME effect is large if the ME coefficient coupling the magnetic and electric fields is large. Experiments on sintered granular composites and on laminated layers of the constituents as well as theories on the interaction between the constituents are described. In the vicinity of electromechanical resonances a ME voltage coefficient of up to 90?V?cm?1?Oe?1 is achieved, which exceeds the ME response of single-phase compounds by 3?5 orders of magnitude. Microwave devices, sensors, transducers and heterogeneous read/write devices are among the suggested technical implementations of the composite ME effect. (ii) In multiferroics the internal magnetic and/or electric fields are enhanced by the presence of multiple long-range ordering. The ME effect is strong enough to trigger magnetic or electrical phase transitions. ME effects in multiferroics are thus 'large' if the corresponding contribution to the free energy is large. Clamped ME switching of electrical and magnetic domains, ferroelectric reorientation induced by applied magnetic fields and induction of ferromagnetic ordering in applied electric fields were observed. Mechanisms favouring multiferroicity are summarized, and multiferroics in reduced dimensions are discussed. In addition to composites and multiferroics, novel and exotic manifestations of ME behaviour are investigated. This includes (i) optical second harmonic generation as a tool to study magnetic, electrical and ME properties in one setup and with access to domain structures; (ii) ME effects in colossal magnetoresistive manganites, superconductors and phosphates of the LiMPO4 type; (iii) the concept of the toroidal moment as manifestation of a ME dipole moment; (iv) pronounced ME effects in photonic crystals with a possibility of electromagnetic unidirectionality. The review concludes with a summary and an outlook to the future development of magnetoelectrics research.
4,315 citations
TL;DR: In this article, the magnetic ordering of the iron ions in bismuth ferrite BiFeO3 was obtained by a study with a high-resolution time-of-flight neutron diffractometer.
Abstract: New information on the magnetic ordering of the iron ions in bismuth ferrite BiFeO3 was obtained by a study with a high-resolution time-of-flight neutron diffractometer. The observed splitting of magnetic diffraction maxima could be interpreted in terms of a magnetic cycloidal spiral with a long period of 620+or-20 AA, which is unusual for perovskites.
1,478 citations
TL;DR: As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with increased suppression of the known spiral spin structure with decreasing nanoparticle size and uncompensated spins and strain anisotropies at the surface.
Abstract: As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period length of ∼62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.
1,129 citations
TL;DR: In this article, the correlation between the power of the excitation laser, the temperature of the sampled spot and the degree of oxidation of magnetite was accurately established, and three independent methods based on the quasi-harmonic approximation and on the ratio of the Stokes to anti-Stokes intensities were used to calculate the local temperature.
Abstract: Natural magnetite (Fe3O4) in the form of single crystal and powder was studied by laser Raman spectroscopy at various laser powers. The correlations between the power of the excitation laser, the temperature of the sampled spot and the degree of oxidation of magnetite were accurately established. In the course of the oxidation of the single crystal of magnetite, the first characteristic features of hematite appear at about 300 and 410 cm−1, at a temperature close to 240°C. This may explain the erroneous assignment of these modes to the intrinsic Raman modes of magnetite in some studies. For the finely powdered magnetite, which is much more easily prone to oxidation, the reaction mechanism proceeds via a metastable maghemite (γ-Fe2O3) before the final product hematite is formed. Three independent methods based on the quasi-harmonic approximation and on the ratio of the Stokes to anti-Stokes intensities were used to calculate the local temperature of the laser-heated spot. Temperature-induced shifts of phonon bands were also evaluated. The phonons shift at the following rates: A1g − 0.023(1) cm−1 K−1, T2g(2) − 0.030(2) cm−1 K−1, Eg − 0.019(5) cm−1 K−1 and T2g(1) − 0.00(1) cm−1 K−1. Copyright © 2003 John Wiley & Sons, Ltd.
515 citations