Magnetization In BiFeO3 Research Articles

Electron-beam evaporated bismuth ferrite (BiFeO3) thin films and characterization

The BiFeO3 (BFO) thin films made by the electron beam evaporator are systematically investigated. As the most difficult part of this work, the preparation process is repeated until the optimal deposition power and elemental composition of BFO are obtained. With the help of X-ray diffraction and Raman spectroscopy, we specify precisely that the sample annealed at the temperature of 650 °C is the purest BFO phase with rhombohedral R3c structure. The Scanning Electron Microscopy images provide the surface morphology and cross-sectional thickness of each sample for the further performance analysis. With the aim of understanding the changes in the chemical bond structure of BFO samples at the different annealing temperatures, we applied X-ray photoelectron spectroscopy and the result indicates that the absorption of oxygen is increasing with the raising of the annealing temperature. Finally, we measured the magnetic property and resistivity of BFO samples to explore their applications. The saturation magnetization measurement shows the correlation between the magnetization of BFO and microstructures such as phase structure, grain size. Meanwhile, the electronic resistivity explains the close relationship between the resistivity and surface morphology.

Interface-Induced Magnetization and Exchange Bias in LSMO/BFO Multiferroic Heterostructures

Interface-induced magnetization in BiFeO3 (BFO) at the La0.67Sr0.33MnO3 (LSMO)/BFO interface is an important factor in determining the magnetoelectric coupling, exchange bias, and other phenomena i...

XAFS investigation of the correlation of Bi-sublattice disorder with ferromagnetism of multiferroic BiFeO3 nanoparticle

Practical utilization of room temperature multiferroic BiFeO3 is intrinsically limited by the absence of ferromagnetism. In this backdrop, development of weak ferromagnetism in 20 nm-sized BiFeO3 nanoparticles is very optimistic. The origin of ferromagnetism is curious and paradoxical from long-range-order perspective since average superexchange angle Fe–O–Fe of the nanoparticle is in antiferromagnetic configuration. In this work, we resolve this paradox by establishing the beneficial role of local disorder with x-ray absorption spectroscopy. We distinguish between the natures of (Bi, Fe)-sublattice disorder and establish their correlation that eventually leads to ferromagnetism. Our results reveal intrinsic large Bi positional disorder, which may be attributed to 6s2 lone pair activity of Bi atom and which leads to greater susceptibility of Bi-sublattice to modification during size reduction. Thus, local (BiO6, FeO6) units are observed to undergo large distortion and rotation respectively. We demonstrate with calculations that FeO6 rotation is geometric consequence of BiO6 distortion. In the case of our BiFeO3 nanoparticles, experimental BiO6 disorder induces FeO6 rotation that drives Fe–O–Fe into ferromagnetic configuration. These local ferromagnetic units give rise to weak magnetism. This structural route to magnetism in BiFeO3 can be generalized to encourage A-site disorder controlled magnetism or any functional octahedral rotation in ABO3 perovsites. The results additionally propagate the effectiveness of particle size-dependence in generating A-site strain rather than chemical doping or external pressure.

ENHANCED FERROELECTRICITY AND FERROMAGNETISM OF (Y, Ni) CO-DOPED BiFeO3 MATERIALS

In this study, multiferroicMultiferroic Bi1-xYxFe0.975Ni0.025O3 (x = 0.00, 0.05, 0.10, and 0.15) called as (Y, Ni) co-doped BiFeO3 materials were synthesized by a sol-gel method. and characterized by X-ray diffraction diagrams and(XRD), energy-dispersive X-ray (EDX) and vibrating sample magnetization (VSM) measurements demonstrated. The result showed that Bi1-xYxFe0.975Ni0.025O3all investigated materials waspresent a single phase of the perovskite-type rhombohedral structure. Ferromagnetism and ferroelectricity of the Bi1-xYxFe0.975Ni0.025O3 materials have been investigated. Results showed that the co-doping by (Y, Ni) for (Bi, Fe) have affected in enhancing by the (Y, Ni) co-doping, as a result the ferroelectric polarization and magnetization of BiFeO3. The magnetic characterization indicated that the ferromagnetic behavior wasthe initial BiFeO3 materialwere enhanced with increasing concentration of Y3+ for (Y, Ni) co-substituted of BiFeO3. Which could beion. It is attributed to the defferentdifference of the magnetic momentmoments of Ni2+ and Fe3+, and+ ions, as well as the Y3+-Fe3+,+ and Y3+-Ni2+ super-exchange interaction. Theinteractions. The characteristics of the investigated materials, such as remanent magnetization (Mr), saturation magnetization (Ms), remanent polarization (2Pr) and saturation polarization (2Ps) continuously increase upon increasing in the range of x from 0.00 to 0.15. When x = 0.15, the values of Mr and Ms are 0.078 and 0.794 emu/g, respectively. The values of 2Pr and 2Ps are 16.58 and 27.99 µC/cm2, respectively. Origin of ferromagnetic and ferroelectric properties of Bi1-xYxFe0.975Ni0.025O3 materials will be discussed in this paper.

Cyclable and non-volatile electric field control of magnetism in BiFeO3 based magnetoelectric heterostructures

Room temperature manipulation of the ferromagnetic state via an electric field is investigated in Ni/BiFe0.95Mn0.05O3 thin film heterostructures. A 600% increase in the magnetic coercive field of the Ni layer is observed at the initial DC electrical poling of the ferroelectric BiFe0.95Mn0.05O3 layer. The magnetoelectric effect is remanent, and the magnetic coercive field can be modulated between a low value and a high value by successively switching the ferroelectric polarization. After the initial poling, the coercive field difference is decreased by subsequent back and forth switching. However, the magnetic bi-stability is preserved at least up to 250 cycles, which is promising for spintronic applications.

Effects of Ti and Mn Co-substitution on P4mm BiFeO3: An Ab Initio Calculation

Tetragonal BiFeO3 (BFO), which has a giant spontaneous polarization, has attracted a great deal of attention recently. In this paper, we systematically study the structural, magnetic, electronic and optic properties of BFO, BiFe0.75Mn0.25O3 (BFMM), and BiFe0.75Ti0.125Mn0.125O3 (BFMT). Results show that doping Ti and Mn into the Fe sites increases the c/a ratio and enhances the magnetization of BiFeO3 from 0 to 5 μB. The crystal symmetry changes from orthogonality to tetragonality with half of the Mn atoms being replaced by Ti in BiFe0.75Mn0.25O3, which suppresses the energy splitting of the Mn 3d orbitals and thus enlarge the band gap to 1.21 eV for BiFe0.75Ti0.125Mn0.125O3. Our calculated Bader charge and charge density difference show that the smallest volume of BiFe0.75Mn0.25O3 arises from the strong Mn–O bonds in BiFe0.75Mn0.25O3. Further investigations indicate similar optical behaviors for BiFeO3 and BiFe0.75Ti0.125Mn0.125O3. However, BiFe0.75Mn0.25O3 exhibits strong absorption in the infrared region for the transition from O 2p to Mn \({e_{g}^{2}}\) and \(t_{2g}^{3}\).

Structural, magnetic and electric properties of Nd and Ni co-doped BiFeO<sub>3</sub> materials

Multiferroic Bi1−xNdxFe0.975Ni0.025O3 (x = 0.00, 0.05, 0.10, 0.125, and 0.15) (BNFNO) and BiFeO3 (BFO) materials were synthesized by a sol-gel method. Crystal structure, ferromagnetic and ferroelectric properties of the as-synthesized materials were investigated. Results showed that Nd3+ and Ni2+ co-doping affected to the electrical leakage, enhanced ferroelectric polarization and magnetization of BiFeO3. Co-doped sample with 12.5 mol% of Nd3+ and 2.5 mol% of Ni2+ exhibited an enhancement in both ferromagnetism and ferroelectric properties up to MS ~ 0.528 emu/g and PS ~ 18.35 μC/cm2 with applied electric field at 5 kV/cm, respectively. The origins of ferromagnetism and ferroelectricity enhancement were discussed in the paper.

Structural and Magnetic Properties of Bi0.5Sr0.5FeO3 Multiferroic Ceramics

Phase pure BiFeO3 (BFO) and Bi0.5Sr0.5FeO3 (BFSO) ceramics were synthesized by solid state reaction method at different sintering conditions. Structural characterization with XRD revealed that the rhombohedral phase changed to cubic due to substitution of Sr in the A- site of BFO. SEM micrographs of BSFO samples indicated improved microstructure with higher density particularly the samples sintered for longer durations. The XPS data suggested the change in oxidation state of Fe from Fe3+ to Fe2+ as a result of aliovalent substitution of Sr at Bi site. As a consequence, oxygen vacancies were created to neutralize charge disorder. The BSFO samples exhibited ferromagnetism with enhanced remnant magnetization and coercive field as compared to the linear magnetization in BFO. These improved results obtained by Sr doping were majorly due to the structural change and creation of oxygen vacancies.

Synthetic magnetoelectric coupling in a nanocomposite multiferroic.

Given the paucity of single phase multiferroic materials (with large ferromagnetic moment), composite systems seem an attractive solution to realize magnetoelectric coupling between ferromagnetic and ferroelectric order parameters. Despite having antiferromagnetic order, BiFeO3 (BFO) has nevertheless been a key material due to excellent ferroelectric properties at room temperature. We studied a superlattice composed of 8 repetitions of 6 unit cells of La0.7Sr0.3MnO3 (LSMO) grown on 5 unit cells of BFO. Significant net uncompensated magnetization in BFO, an insulating superlattice, is demonstrated using polarized neutron reflectometry. Remarkably, the magnetization enables magnetic field to change the dielectric properties of the superlattice, which we cite as an example of synthetic magnetoelectric coupling. Importantly, controlled creation of magnetic moment in BFO is a much needed path toward design and implementation of integrated oxide devices for next generation magnetoelectric data storage platforms.

Enhanced magnetic properties of chemical solution deposited BiFeO3 thin film with ZnO buffer layer

Magnetic properties of BiFeO3 films deposited on Si substrates with and without ZnO buffer layer have been studied in this work. We adopted the chemical solution deposition method for the deposition of BiFeO3 as well as ZnO films. The x-ray diffraction measurements on the deposited films confirm the formation of crystalline phase of BiFeO3 and ZnO films, while our electron microscopy measurements help to understand the morphology of few micrometers thick films. It is found that the deposited ZnO film exhibit a hexagonal particulate surface morphology, whereas BiFeO3 film fully covers the ZnO surface. Our magnetic measurements reveal that the magnetization of BiFeO3 has increased by more than ten times in BiFeO3/ZnO/Si film compared to BiFeO3/Si film, indicating the major role played by ZnO buffer layer in enhancing the magnetic properties of BiFeO3, a technologically important multiferroic material.

Effects of local structural distortion on magnetization in BiFeO3 with Pr, Ba co-doping

Effects of local structural distortion on magnetization in BiFeO3(BFO) with Pr and Ba co-doping were systematically investigated. A structural phase transition of rhombohedral-to-cubic occurs in Bi0.75Pr0.15Ba0.1FeO3 sample. The strong enhancement of the spontaneous magnetization is significantly affected by the local lattice distortion and collapse of the spatial spin structure. Charge compensation is very possible while Pr4+ and Ba2+ replacing for Bi3+ together in BFO, which may suppress the charge defects and decrease the magnetism.

Ab initio study on phase transition and magnetism of BiFeO3 under pressure

In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure of phase transition is reached. The critical pressure for the insulator–metal transition (IMT) is found to be about 50 GPa. A pressure induced crossover of high-spin states and low-spin states is observed close to the IMT pressure in R3c structure. The LSDA+U calculations account well for the mechanism of the IMT and crossover of spin states predicted in recent experiment (Ref.[1]).

Formation of magnetite in bismuth ferrrite under voltage stressing

Micro-Raman studies show that under ∼700kV∕cm of dc voltage stressing for a few seconds, magnetite Fe3O4 forms in thin-film bismuth ferrite BiFeO3, probably due to phase separation. No evidence is found spectroscopically of hemite α-Fe2O3, maghemite γ-Fe2O3, or Bi2O3. This may relate to the controversy regarding the magnitude of magnetization in BiFeO3.

Microstructure and phase control in Bi–Fe–O multiferroic nanocomposite thin films

We report on the controlled multiphase thin film growth in the Bi–Fe–O system. By varying the deposition oxygen pressure, the dominant phase formed in the film continuously changes from ferroelectric BiFeO3 to a mixture of α-Fe2O3 and ferromagnetic γ-Fe2O3. X-ray diffraction and high-resolution transmission electron microscopy have revealed that epitaxial multiferroic nanocomposites consisting of BiFeO3 and Fe2O3 are formed when the deposition pressure is ≈5mTorr. In order to investigate the previously reported anomalous enhancement in magnetization in BiFeO3, we have fabricated a thickness gradient pure BiFeO3 film. The out-of-plane lattice constant was found to increase continuously as the thickness is decreased from 300 to 5nm, but no significant enhancement in magnetization was observed.

Phase transition with suppression of magnetism in BiFeO3 at high pressure

The magnetic behavior of a Bi57FeO3 powdered sample was studied at high pressures by the method of nuclear forward scattering (NFS) of synchrotron radiation. The NFS spectra from 57Fe nuclei were recorded at room temperature under high pressures up to 61.4 GPa, which were created in a diamond anvil cell. In the pressure interval 0 < P < 47 GPa, the magnetic hyperfine field H Fe at the 57Fe nuclei increased reaching a value of ∼52.5 T at 30 GPa, and then it slightly decreased to ∼49.6 T at P = 47 GPa. As the pressure was increased further, the field H Fe abruptly dropped to zero testifying a transition from the antiferromagnetic to a nonmagnetic state (magnetic collapse). In the pressure interval 47 < P < 61.4 GPa, the value of H Fe remained zero. The field H Fe recovered to the low-pressure values during decompression.