Ab initio study of electrons and phonons in multiferroic BiFeO3
Lead Research Organisation:
UNIVERSITY OF EXETER
Department Name: Physics
Abstract
Multiferroic materials exhibit two or more properties of ferromagnetism (or antiferromagnetism), ferroelectricity (or antiferroelectricity) and ferroelasticity. Such materials can develop electric polarisation when subjected to an external magnetic field, and can develop magnetisation when subjected to an external electric field. The perovskite BiFeO3 is known to be the only material that exhibits multiferroism at room temperature. In single crystal form itis rhombohedrally distorted perovskite with space group R3c, and is ferroelectric and exhibits antiferromagnetic behaviour up to 643 K. Such 'magneto-electric' materials have technological applications as Hall probes, UHF spin-wave oscillators, and can also be employed in potential applications in information storage, in the emerging field of spintronics, and sensors.Several works have recently been done on the study of the structural, electronic and magnetic properties of BiFeO3. In its single crystal rhombohedral phase it shows only small values of ferroelectric polarisation. However, epitaxially grown films with (001)-oriented pseudotetragonal structure shows an order of magnitude higher polarisation. Polarlized Raman scattering method has been employed to examine some phonon modes for the tetragonal phase. However, no systematic studied have emerged on dynamical properties, e.g. mode assignment and full phonon dispersion relations. As a wide range ofphysical properties of solids depend on their lattice dynamical properties, it is important to undertake a systematic study of phonons for the two structural phases (rhombohedral and tetragonal). Due to the presence of localised Fe 3d electronic states, it is further desirable to investigate changes in phonon modes due to electronic effects such as spin polarisation and strong Coulomb repulsion between the localised states.The proposed research is aimed at carrying out ab-inito theoretical and computational studies of the electronic structure and phonon modes in the multiferroic crystal BiFO3. Our work is expected to help experimentalists analyse their Raman scattering measurements.
Organisations
People |
ORCID iD |
| Gyaneshwar Srivastava (Principal Investigator) |
Publications
Thomas I
(2016)
Lattice thermal conduction in ultra-thin nanocomposites
in Journal of Applied Physics
Tütüncü H
(2008)
Electronic structure and zone-center phonon modes in multiferroic bulk BiFeO3
in Journal of Applied Physics
Tütüncü H
(2008)
Electronic structure and lattice dynamical properties of different tetragonal phases of BiFeO 3
in Physical Review B
| Description | Multiferroic materials exhibit two or more properties of ferromagnetism (or antiferromagnetism), ferroelectricity (or antiferroelectricity) and ferroelasticity. Such materials can develop electric polarisation when subjected to an external magnetic field, and can develop magnetisation when subjected to an external electric field. The perovskite BiFeO_3 (usually referred to as BFO) is known to be the only material that exhibits multiferroism at room temperature. In single crystal form it is rhombohedrally distorted perovskite with space group R3c, and is ferroelectric and exhibits antiferromagnetic behaviour up to 643 K. Such 'magneto-electric' materials have technological applications as Hall probes, UHF spin-wave oscillators, and can also be employed in potential applications in information storage, in the emerging field of spintronics, and sensors. This proposal seeks to characterize the tetragonal and rhombohedral phases of single-crystal BiFeO_3 by making detailed ab initio studies of its electronic structure and phonon dispersion relations. An important aspect of such studies would be to assess the role of the electronic structure on phonon modes. The narrow Fe 3d states are expected to play an important role in determining the electronic density of states. This requires that the electronic state calculations be performed within the spin density functional scheme and also by including a scheme to deal with the highly localized nature of the Fe 3d electrons. We have concluded that the meta-stable tetragonal phase is characterised by the ratio c/a=1.264, much larger than proposed earlier (c/a=1.016) by pulsed deposition using a small laser frequency. For the equilibrium geometry, the meta-stable tetragonal phase is semiconducting with a direct band gap of approximately 0.55 eV, much smaller than the (indirect) band gap for the rhombohedral phase. The magnetic moment per Fe atom (within the sGGA scheme) in the tetragonal phase of 4.90 µ_B is larger than 4.25 µ_B in the rhombohedral phase. Our studies provide a clearer analysis of the energy values and polarisation characteristics of the Raman active phonon modes than is available from existing theoretical and experimental studies. The highest zone-centre mode has the following characteristics: Rhombohedral (R3c) phase: the mode at ~594 1/cm, of A_2 representation with LO-TO mixed character, is Raman inactive and originates from vibrations of the equitorial oxygen plane, with larger amplitude along [111] (i.e. along the z axis, making it LO-like). Tetragonal (P4mm) phase: the mode at ~662 1/cm, of A_1 representation, is Raman active and results largely from LO vibrations of the axial oxygen atoms. |
| Exploitation Route | For further theoretical studies of the electronic structure and phonon dispersion relations in this material. |
| Sectors | Education |
| Description | Multiferroic materials exhibit two or more properties of ferromagnetism (or antiferromagnetism), ferroelectricity (or antiferroelectricity) and ferroelasticity. Such materials can develop electric polarisation when subjected to an external magnetic field, and can develop magnetisation when subjected to an external electric field. The perovskite BiFeO_3 (usually referred to as BFO) is known to be the only material that exhibits multiferroism at room temperature. In single crystal form it is rhombohedrally distorted perovskite with space group R3c, and is ferroelectric and exhibits antiferromagnetic behaviour up to 643 K. Such 'magneto-electric' materials have technological applications as Hall probes, UHF spin-wave oscillators, and can also be employed in potential applications in information storage, in the emerging field of spintronics, and sensors. This proposal seeks to characterize the tetragonal and rhombohedral phases of single-crystal BiFeO_3 by making detailed ab initio studies of its electronic structure and phonon dispersion relations. An important aspect of such studies would be to assess the role of the electronic structure on phonon modes. The narrow Fe 3d states are expected to play an important role in determining the electronic density of states. This requires that the electronic state calculations be performed within the spin density functional scheme and also by including a scheme to deal with the highly localized nature of the Fe 3d electrons. We have concluded that the meta-stable tetragonal phase is characterised by the ratio c/a=1.264, much larger than proposed earlier (c/a=1.016) by pulsed deposition using a small laser frequency. For the equilibrium geometry, the meta-stable tetragonal phase is semiconducting with a direct band gap of approximately 0.55 eV, much smaller than the (indirect) band gap for the rhombohedral phase. The magnetic moment per Fe atom (within the sGGA scheme) in the tetragonal phase of 4.90 µ_B is larger than 4.25 µ_B in the rhombohedral phase. Our studies provide a clearer analysis of the energy values and polarisation characteristics of the Raman active phonon modes than is available from existing theoretical and experimental studies. The highest zone-centre mode has the following characteristics: Rhombohedral (R3c) phase: the mode at ~594 1/cm, of A_2 representation with LO-TO mixed character, is Raman inactive and originates from vibrations of the equitorial oxygen plane, with larger amplitude along [111] (i.e. along the z axis, making it LO-like). Tetragonal (P4mm) phase: the mode at ~662 1/cm, of A_1 representation, is Raman active and results largely from LO vibrations of the axial oxygen atoms. |
| First Year Of Impact | 2006 |
| Sector | Education |
| Impact Types | Societal |