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Hong-Jian Feng

Publications and source records attributed to Hong-Jian Feng.

13 recordsLinked to original sources
arXiv2014

Electronic structures and lattice dynamics of BaTiO3 and BiFeO3 : a comparative first-principles study

First-principles calculations were performed to investigate the ferroelectric properties of barium titanate and bismuth ferrite, as well as phonon dispersion of BaTiO3, using density functional theory and density functional perturbation theory. Results show that the strong hybridization of Ti-O and Bi-O lead to the corresponding mechanisms for stabilizing the distorted structure. The spontaneous polarization of 59.4 μC/cm2 and 27.6 μC/cm2 were calculated for BiFeO3 and BaTiO3 respectively, using berry phase method within the modern theory of polarization. The stereochemical activity of Bi-6s long-pair, which was the driven mechanism for ferroelectricity in BiFeO3, was able to produce greater polarization than the Ti off-centring displacement in BaTiO3. New multiferroic perovskite type materials combined with these two ferroelectric instabilities were predicted to have a better ferromagnetic ordering in comparison with BiFeO3.

cond-mat.mtrl-sci↗
arXiv2014

Enhanced optical properties and the origin of carriers transport in BiFeO$_3$/TiO$_2$ heterostructures with 109$^{\circ}$ domain walls

The absorption performance in the BiFeO$_3$/TiO$_2$ bilayer film prepared by simple sol-gel method has been significantly improved in the ultraviolet and visible-light region, comparing with BiFeO$_3$ and TiO$_2$ films. Terahertz-radiation emission presents a direct evidence of photon-induced electrons and holes transport in the heterostructures. First-principles calculations agree well with the experiments and present an unambiguous explanation of charge carriers transport and enhanced absorbance which is induced by the large electrostatic potential drop in the interface of heterostructures with the 109$^{\circ}$ domain walls. This work provides a promising candidate toward designing novel photovoltaic BiFeO$_3$-based heterostructures with high efficiencies.

cond-mat.mtrl-sci↗
arXiv2013

Photovoltaic effect in BiFeO3/TiO2 heterostructures tuned with epitaxial strain and an electric field

The photovoltaic effect in the BiFeO3/TiO2 heterostructures can be tuned by epitaxial strain and an electric field in the visible-light region which is manifested by the enhancement of absorption activity in the heterojunction under tensile strain and an electric field based on the first-principles calculations. It is suggested that there are coupling between photon, spin carrier, charge, orbital, and lattice in the interface of the bilayer film which makes the heterojunction an intriguing candidate towards fabricating the multifunctional photoelectric devices based on spintronics. The microscopic mechanism involved in the heterostruces is related deeply with the spin transfer and charge rearrangement between the Fe 3d and O 2p orbitals in the vicinity of the interface.

cond-mat.mtrl-sci↗
arXiv2013

Spin transfer in ultrathin BiFeO3 film under external electric field

First-principals calculations show that up-spin and down-spin carriers are accumulating adjacent to opposite surfaces of BiFeO3(BFO) film with applying external bias. The spin carriers are equal in magnitude and opposite in direction, and down-spin carriers move to the direction opposing the external electric field while up-spin ones along the field direction. This novel spin transfer properties make BFO film an intriguing candidate for application in spin capacitor and BFO-based multiferroic field-effect device.

cond-mat.mtrl-sci↗
arXiv2013

Electric-field switching magnetization and spin transfer in ultrathin BiFeO3 film

First-principles density-functional theory calculations show switching magnetization by 90 degree can be achieved in ultrathin BFO film by applying external electric-field. Up-spin carriers appear to the surface with positive field while down-spin ones to the negative field surface, arising from the redistribution of Fe-t2g orbital. The half-metallic behavior of Fe-3d states in the surface of R phase film makes it a promising candidate for AFM/FM bilayer heterostructure possessing electric-field tunable FM magnetization reversal and opens a new way towards designing spintronic multiferroics. The interface exchange-bias effect in this BFO/FM bilayer is mainly driven by the Fe-t2g orbital reconstruction, as well as spin transferring and rearrangement.

cond-mat.mtrl-sci↗
arXiv2012

The role of Coulomb and exchange interaction on the Dzyaloshinskii-Moriya interaction(DMI) in BiFeO3

Ab initio calculations show that the Dzyaloshinskii-Moriya interaction(DMI)and net magnetization per unit cell in BiFeO3 are reduced when U is increasing from 0 to 2.9 eV, and independent of $J$. Interestingly, the DMI is even destroyed as $U$ exceeds a critical value of 2.9 eV. We propose a simple model to explain this phenomenon and present the nature of the rotation of the magnetization corresponding to altered antiferrodistortive distortions under DMI in BiFeO3.

cond-mat.mtrl-sci↗
arXiv2012

Magnetism and electronic properties of BiFeO3 under lower pressure

Ab initio calculations show an antiferromagnetic-ferromagnetic phase transition around 9-10 GPa and a magnetic anomaly at 12 GPa in BiFeO3. The magnetic phase transition also involves a structural and insulator-metal transition. The G-type AFM configuration under pressure leads to an increase of the y component and decrease of the z component of the magnetization, which is caused by the splitting of the dz2 orbital from doubly degenerate eg states. Our results agree with recent experimental results.

cond-mat.mtrl-sci↗
arXiv2012

The reversal of magnetization driven by the Dzyaloshinskii-Moriya interaction(DMI) in perovskite Bi2FeMnO6

Ab initio calculations show that the coupling between antiferrodistortive(AFD) distortions and magnetization in perovskite Bi2FeMnO6 is prohibited to make magnetization rotate as on-site Coulomb interaction($U$) is larger than 2.7 eV, where anomalies in antiferromagnetic(AFM) vectors and band gap varying with on-site Coulomb interaction can be observed. This coupling is attributed to the antisymmetric Dzyaloshinskii-Moriya interaction(DMI) driven by the eg-eg states AFM interaction and charge redistribution with respect to different AFD distortions.

cond-mat.mtrl-sci↗
arXiv2007

Ab initio prediction on ferrotoroidic olivine Li4MnFeCoNiP4O16

First-principles calculation predict that olivine Li4MnFeCoNiP4O16 has ferrotoroidic characteristic and ferrimagnetic configuration with magnetic moment of 1.56 \muB per formula unit. The ferrotoroidicity of this material makes it a potential candidate for magnetoelectric materials . Based on the orbital-resolved density of states for the transtion-metal ions in Li4MnFeCoNiP4O16, the spin configuration for Mn2+,Fe3+,Co2+, and Ni2+ is t2g3eg2, t2g3eg2,t2g1t2g3eg1eg2, and t2g2t2g3eg1eg2, respectively. Density functional theory plus U (DFT+U) shows a indirect band gap of 1.25 eV in this predicted material, which is not simply related to the electronic conductivity in terms of being used as cathode material in rechargeable Li-ion batteries.

cond-mat.mtrl-sci↗
arXiv2007

First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6

First principles calculations based on the density functional theory within the local spin density approximation plus U(LSDA+U)scheme, show rhombohedral Bi$_2$FeTiO$_6$ is a potential multiferroic in which the magnetism and ferroelectricity coexist . A ferromagnetic configuration with magnetic moment of 4 $μ_B$ per formula unit have been reported with respect to the minimum total energy. Spontaneous polarization of 27.3 $μ$ C/cm$^2$, caused mainly by the ferroelectric distortions of Ti, was evaluated using the berry phase approach in the modern theory of polarization. The Bi-6s stereochemical activity of long-pair and the `d$^0$-ness' criterion in off-centring of Ti were coexisting in the predicted new system. In view of the oxidation state of Bi$^{3+}$,Fe$^{2+}$,Ti$^{4+}$, and O$^{2-}$ from the orbital-resolved density of states of the Bi-6p, Fe-3d,Ti-3d, and O-2p states,the valence state of Bi$_2$FeTiO$_6$ in the rhombohedral phase was found to be Bi$_2$$^{3+}$Fe$^{2+}$Ti$^{4+}$O$_6$.

cond-mat.mtrl-sci↗
arXiv2007

Electronic structure of BaFeO3: an abinitio DFT study

First principles calculations were performed to study the ground state electronic properties of BaFeO3 (BFO) within the density functional theory (DFT). Adopting generalized gradient approximation (GGA) exchange and correlation functional and Vosko-Wilk-Nusair correlation energy functional interpolation, we have systematically conducted the band structure, density of states and electronic distribution along different crystalline planes. Calculating results show that band gap in the majority spin band structure and band gap in the minority spin band structure were found to be 2.7012 eV and 0.6867 eV respectively. Up-spin Fe t2g were fully occupied and down-spin Fe eg were empty. Moreover, the up-spin Fe eg and down-spin Fe t2g were partially occupied near the Fermi energy, leading to a finite density of states. The Fe4+-O-Fe4+ plane superexchange coupling should rearrange the magnetic order to make the ferromagnetic characteristic being possible, moreover the tetragonal displacement along the c axis could induce the perovskites materials to acquire ferroelectric property. These reasons could lead to the fact that the tetragonal phase BFO could be a potential multiferroics while it was produced under the very experimental conditions. The charge density along different crystalline planes were illustrated to show that strong covalent bonding between O and Fe can be used to investigate the exchange coupling, and this strong hybridization may further increase the superexchange coupling to enhance the magnetic ordering.

cond-mat.mtrl-sci↗
arXiv2007

Electronic structure of barium titanate : an abinitio DFT study

First principle calculations were performed to study the ground state electronic properties of Barium titanate within the density functional theory (DFT). In our DFT computations, we used Vosko-Wilk-Nusair correlation energy functional and generalized gradient approximation (GGA) exchange and correlation energy functional as suggested by Perdew and Wang (PWGGA). The band structure, total density of states (DOS) and partial DOS have been systematically conducted to investigate the electronic configuration of this prototype ferroelectric perovskits compound. The band gap was 1.92 eV within our approach, and the quasi-flat band at -17 eV and -10 eV were attributed to the O 2s and Ba 5p states respectively, which was in good agreement with the corresponding total DOS and partial DOS. From the DOS investigation, it can be seen that the Ti eg state intended to interact with the oxygen octahedral orbitals to form the p-d hybridization. Moreover the strong p-d overlap and bonding can be observed in the electronic density redistribution along the different crystalline planes with respect to the corresponding space group, and the electronic isodense have been shown along the (001), (100), (110) and (111) crystal planes. From these electronic density maps, the strong bonding between Ti and O atoms can even be observed in the (111) crystalline plane.

cond-mat.mtrl-sci↗