Synthesis,structural and magnetic characterization of highly ordered single crystalline BiFeO3 nanotubes

In this work, we report on the fabrication of highly ordered single crystalline BiFeO₃ (BFO) nanotubes by a sol–gel technique using two-step anodic aluminum oxide (AAO) as template. We prepared BFO nanotubes with dimensions of 65 nm in diameter and 3 μm in length, as confirmed by scanning electron microscopy (SEM) measurements. The obtained single crystalline nanotubes present the expected pure phase (BiFeO₃) as confirmed by energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). In addition to the antiferromagnetic behavior, the magnetization curves of the BFO nanotubes also present a ferromagnetic response, which holds from 2 to 300 K. This desirable behavior is associated to the break of the antiferromagnetic helical spin ordering of the BFO nanotubes. Besides the magnetocrystalline anisotropy, the large length-to-diameter ratio induced an uniaxial shape anisotropy, attested by the applied magnetic field angle measurements.     

Raman and electrical studies of multiferroic BiFeO3

Monophasic rhombohedral structure of BiFeO₃ electroceramic is successfully synthesized by conventional solid state reaction route followed by slow step sintering schedule. Effect of sintering temperature is found to greatly influence its structural, dielectric, ferroelectric, capacitance and leakage behavior of bulk ceramic. From XRD analysis it is seen that at lower sintering temperature (750 °C) bulk BiFeO₃ sample showed rhombohedral structure (R3c) along with few impurity phases, which become suppressed at higher sintering temperature and facilitates the compactness of grains and formation of dense microstructure. The leakage current and capacitive characteristic of the sample was improved significantly with increase in sintering temperature of BiFeO₃ (850 °C). At higher sintering temperature, ferroelectric behavior of the sample is found to change its shape from semi elliptical lossy P–E features to a typical ferroelectric loop with improvement of its remnant as well as saturation polarization value. Raman spectra over the frequency range of 100–700 cm^?1 have been systematically investigated. Besides the changes of the peak position and the line width of all modes, the prominent frequency shift, the line broadening and variation of the intensity were observed with increase in sintering temperature.     

Dipole skyrmion vortices in multiferroic BiFeO3

This paper presents finite difference calculations of a dipole skyrmion vortex in multiferroic BiFeO₃ and demonstrates a stabilizing role of electrostatic dipole-dipole interaction. We consider the main approaches to producing vortex lattices in BiFeO₃ and their potential applications in spintronics and diptronics.     

Investigation on multiferroic properties of BiFeO3 ceramics

BiFeO₃ polycrystalline ceramics was prepared by solid-state reaction method and its structural, optical and magnetic properties were investigated. BiFeO₃ was synthesized in a wide range of temperature (825–880 °C) and a well crystalline phase was obtained at a sintering temperature of 870 °C. X-ray diffraction patterns of the samples were recorded and analyzed for the confirmation of crystal structure and the determination of the lattice parameters. The average grain size of the samples was found to be between 1–2 μm. The determined value of direct bandgap of BiFeO₃ ceramics was found to be 2.72 eV. The linear behavior of M-H curve at room temperature confirmed antiferromagetic properties of the BiFeO₃ (BFO). S shaped M-H curve was obtained at a temperature of 5 K. In the whole temperature measurement range (5–300 K) of M-T, no anomalies were observed due to high Curie temperature and Neel temperature of the BiFeO₃.     

Size-dependent magnetic properties of single-crystalline multiferroic BiFeO3 nanoparticles

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 approximately 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.     

Magnetic and electrical properties of multiferroic BiFeO3, its synthesis and applications

Major ways to improve the magnetic and electrical properties of promising multiferroic BiFeO₃ and optimize its synthesis have been studied, and its applications in spintronics, photonics, and magnonics have been discussed.     

Sol–gel synthesis and properties of multiferroic BiFeO3

High purity multiferroic BiFeO₃ (BFO) powders were synthesized by sol–gel process using bismuth nitrate and iron nitrate as sources. The BFO powders annealed at 600 °C in nitrogen environment were mainly composed of a rhombohedral BiFeO₃ phase (R-phase) with a minor impurity phase of Bi₂O₃. A pure BFO R-phase has been obtained by leaching out the minor Bi₂O₃ phase using diluted nitric acid. A reversible phase transformation of the BFO R-phase has been detected at 836 °C by a differential thermal analysis. The powders of BFO R-phase exhibits a uniform feature with the particle size of ∼200 nm. The dielectric constant of the BFO R-phase is measured to be ∼15 in the frequency range of 10⁴∼10⁶ Hz at room temperature.     

Non-volatile domain nucleation and growth in multiferroic BiFeO3 films

We have presented a systematical study of the domain nucleation and growth behaviors in multiferroic BiFeO(3) (BFO) films. Both the ferroelectric and the ferroelastic switching dynamics were investigated. Several environmental parameters, including the polarization orientations, the monodomain-like matrix, and the ordered domain walls as local boundaries, were well controlled by thin-film strain engineering through changing the vicinal angles of the substrates. The tip-based domain dynamics was studied by subsequent piezoresponse force microscope (PFM) imaging of the domain evolution under external voltage pulses. For the nanodomains written in the monodomain-like environment, the domain wall performed the thermal activated motion. The as-grown 71° domain walls can act as pinning centers for the ferroelectric domain growth driven by low fields; moreover, ferroelastic nucleation near a 71° domain wall will cause the deformation of the domain wall. The ferroelastic domain growth possessed relatively small activation fields, and therefore usually performed non-activated motion. This study revealed the effects of local environments on the dynamics forming nanoscale domains, and opened a pathway for applications in novel non-volatile functional devices.     

Enhanced magnetoelectric response of Mn-doped BiFeO3-based multiferroic ceramics

Journal of Materials Science: Materials in Electronics - Our previous work proposed that except for ferromagnetic and piezoelectric properties, mechanical quality factor is also an important...     

Structural, dielectric and multiferroic properties of Er and La substituted BiFeO3 ceramics

Erbium (Er) and lanthanum (La) substituted BiFeO₃ (BFO) ceramics have been prepared through conventional solid solution route. X-ray diffraction data indicated a gradual phase transition from rhombohedral to monoclinic structure in Bi_0·9?x La_0·1Er _x FeO₃ (x = 0·05, 0·07 and 0·1) (BLEFO _{x = 0·05, 0·07, 0·1}) ceramics. Differential thermal analysis (DTA) measurements of BFO samples showed a ferroelectric transition at 835°C, whereas it is shifted to 792°C for BLEFO _{x = 0·1}. The Raman spectra of BLEFO _{x = 0·05, 0·07, 0·1} samples showed the shift of Raman modes to higher wavenumbers and suppression of A₁ modes indicating decrease in ferroelectricity. The Raman spectra also indicated the structural transformation due to Er and La substitution in BFO. On subsequent erbium doping, the intrinsic dielectric constant is found to decrease from 68 (for pure BFO) to 52 for BLEFO _{x = 0·05} to 43 for BLEFO _{x = 0·07} but increased to 89 for BLEFO _{x = 0·1} when compared to pure BFO. The increase in Er content resulted in the increase in spontaneous magnetization (0·1178 emu/g at 8T for BLEFO _{x = 0·1}) due to collapse of spin cycloid structure. Ferroelectric remnant polarization of BLEFO _{x = 0·05} and BLEFO _{x = 0·07} decreases when compared to pure BFO while small remnant polarization (close to paraelectric behaviour) is evident for BLEFO _{x = 0·1}.     

Structure transition and multiferroic properties of Mn-doped BiFeO3 thin films

Pure BiFeO₃ (BFO) and Mn-doped BiFe_1?yMn_yO₃ thin films were prepared on FTO/glass (SnO₂: F) substrates by using a sol–gel method. The effects of Mn-doping on the structure and electric properties of the BFO thin films were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the Mn-doped BiFe_0.96Mn_0.04O₃ (BFMO) thin film. The Rietveld refined XRD patterns conform the trigonal (R3c: H) and tetragonal (P422) symmetry for the BFO and BFMO thin films, respectively. The structure transition and the mixed valences of Mn ions substantially improve the electric properties of the BFMO thin film. The remnant polarization (P _r) of the BFMO thin film was 105.86 μC/cm² at 1 kHz in the applied electric field of 865 kV/cm. At an applied electric field of 150 kV/cm, the leakage current density of BFMO thin film is 1.42 × 10^?5 A/cm². It is about two orders of magnitude lower than that of the pure BFO thin film (1.25 × 10^?3 A/cm²). And the enhanced saturated magnetization of the BFMO thin film is 4.45 emu/cm³.     

Nanodots of multiferroic oxide material BiFeO3 from the first Principles

Multiferroic nanodots can be harnessed to aid the development of the next generation of nonvolatile data storage and multi-functional devices. In this paper, we review the computational aspects of multiferroic nanodot materials and designs that hold promise for the future memory technology. Conception, methodology, and systematical studies are discussed, followed by some up-to-date experimental progress towards the ultimate limits. At the end of this paper, we outline some challenges remaining in multiferroic research, and how the first principles based approach can be employed as an important tool providing critical information to understand the emergent phenomena in multiferroics.     

Spin-phonon coupling and improved multiferroic properties of Zr substituted BiFeO3 nanoparticles

Zr substituted BiFeO₃ (BiFe_1?xZr_xO₃ with x = 0.03, 0.07, 0.10 and 0.15) nanoparticles were synthesized by sol–gel method. Powder X-ray diffraction studies showed rhombohedral crystal structure for x = 0.03–0.10 samples. The substitution induced structural transformation from rhombohedral to triclinic phase has been observed for x = 0.15. Raman analysis confirmed this structural transformation as also the distortion induced spin phonon coupling. Enhanced magnetic behaviour with saturation magnetization of 7.62 emu/g has been observed in x = 0.07 sample. The dielectric measurements indicated the strong magneto-electric coupling in the range of Neel temperature. The impedance study over a wider frequency and temperature range suggests decrease in conductivity in the samples with increasing Zr concentration. UV–Vis diffuse reflectance spectra shows the strong absorption of visible light suggesting the band gap values from 2.22 to 2.15 eV corresponding to x = 0.03–0.15 compositions.     

Ferroelectric and magnetic properties of multiferroic BiFeO(3)-based composite films

BiFeO(3)-based composite films were fabricated onto the Pt/Ti/SiO(2)/Si(100) substrates by a chemical solution deposition (CSD) method using the precursor solutions with various excess iron composition followed by annealing at 923 K for 30 minutes under oxygen gas flow. Coexistence of spontaneous magnetization and remanent polarization could be obtained in the BiFeO(3)-based composite films with high excess iron composition. The remanent magnetization of almost 20 emu/cm(3) and the magnetic coercive field of 1.5 kOe were obtained at the iron composition ratio of Fe/Bi = 1.25. In this specimen, the remanent polarization at 90 K was approximately 10 microC/cm(2) at the electric field of 1500 kV/cm. Structural analysis suggested that the remanent polarization has a possibility to increase by suppressing the formation of the secondary phases of Bi(2)Fe(4)O(9) and alpha-Fe(2)O(3), these are the nonferroelectric material as well as antiferromagnetic phase.