Browsing by Author "Reynolds, NM"

Now showing 1 - 8 of 8
  • Thumbnail Image
    Item
    18O isotope substitution on the multiferroic compound DyMnO3
    (Australian Institute of Physics, 2013-02-06) Narayanan, N; Li, F; Hutchison, WD; Reynolds, NM; Rovillain, P; Ulrich, C; Hester, JR; McIntyre, GJ; Mulders, AM
    Not available
  • Thumbnail Image
    Item
    Effects of 18O isotope substitution in multiferroic RMnO3 (R=Tb, Dy)
    (Australian Institute of Physics, 2015-02-02) Graham, PJ; Narayanan, N; Reynolds, NM; Li, F; Rovillain, P; Bartkowiak, M; Hester, JR; Kimpton, JA; Yethiraj, M; Pomjakushina, E; Conder, K; Kenzelmann, M; McIntyre, GJ; Hutchison, WD; Ulrich, C
    Multiferroic materials demonstrate desirable attributes for next-generation multifunctional devices as they exhibit coexisting ferroelectric and magnetic orders. In type-II multiferroics, coupling exists that allows ferroelectricity to be manipulated via magnetic order and vice versa, offering potential in high-density information storage and sensor applications. Despite extensive investigations into the subject, questions of the physics of magnetoelectric coupling in multiferroics remain, and competing theories propose different mechanisms. The aim of this investigation was to study changes in the statics and dynamics of structural, ferroelectric and magnetic orders with oxygen-18 isotope substitution to shine light into the coupling mechanism in multiferroic RMnO3 (R=Tb, Dy) systems. We have performed Raman spectroscopy on 16O and 18O-substituted TbMnO3 single crystals. Oxygen-18 isotope substitution reduces all phonon frequencies significantly. However, specific heat measurements determine no changes in Mn3+ (28 and 41 K) magnetic phase transition temperatures. Pronounced anomalies in peak position and linewidth at the magnetic and ferroelectric phase transitions are seen. While the anomalies at the sinusoidal magnetic phase transition (41 K) are in accordance to the theory of spin-phonon coupling, further deviations develop upon entering the ferroelectric phase (28 K). Furthermore, neutron diffraction measurements on 16O and 18O-substituted DyMnO3 powders show structural deviations at the ferroelectric phase transition (17 K) in the order of 100 fm. These results indicate that the structure is actively involved in the emergence of ferroelectricity in these materials.
  • Thumbnail Image
    Item
    Inelastic neutron scattering in multiferroic materials
    (Australian Institute of Physics, 2012-02-02) Reynolds, NM; Graham, PJ; Mulders, AM; McIntyre, GJ; Dainlkin, SA; Fujioka, J; Tokura, Y; Keimer, B; Reehuis, M; Ulrich, C
    In order to obtain a deeper understanding of the spin interactions between the magnetic moments of the Tb-ions and the Mn-ions in multiferroic TbMnO3, inelastic neutron scattering experiments (at the ILL in Grenoble and the Bragg Institute at ANSTO) are performed on isostructural, non-multiferroic TbVO3. Acoustic and optical magnon branches are identified at energies comparable to the spin wave excitation spectrum of YVO3. In addition, a crystal field excitation arising from the Tb-ions is identified at the energy of 14.9 meV. This is substantially larger than the crystal field excitation at 4.5 meV in TbMnO3.
  • Thumbnail Image
    Item
    Inelastic neutron scattering in multiferroic materials
    (Australian Institute of Physics, 2012-02-02) Reynolds, NM; Graham, P; Mulders, AM; McIntyre, G; Danilkin, SI; Fujioka, J; Tokura, Y; Keimer, B; Reehuis, M; Ulrich, C
    Magnetism and ferroelectricity are both exciting physical properties and are used in everyday life in sensors and data storage. Multiferroic materials are materials where both properties coexist. They offer a great potential for future technological applications like the increase of data storage capacity or in novel senor applications. The coupling mechanism between both antagonistic effects, electrical polarization and magnetic polarization, is not fully understood yet. The aim of the project is the systematic study of multiferroic materials such as TbMnO3 and related materials by inelastic neutron scattering (INS) in order to obtain a deeper insight into the interplay between the two interacting effects. We have started our investigations with TbVO3, which is isostructural to TbMnO3, but has a collinear antiferromagnetic spin arrangement [1] instead of a cycloidal spin structure [2]. By using inelastic neutron scattering (INS) we have obtained the spin wave dispersion relation and the crystal field excitations of the Tb-ions in TbVO3. These data will be compared with previously obtained data of D. Senff on TbMnO3 [3]. Experiments were performed at the ILL in Grenoble, France and at the research reactor OPAL at ANSTO, Australia.
  • Thumbnail Image
    Item
    Investigations into the magnetic and crystal field excitations of the orthorhombically distorted perovskites RVO3 (R=Dy, Tb, Pr, Ce)
    (Australian Institute of Physics, 2013-02-06) Reynolds, NM; Rovillain, P; Danilkin, SA; Schmalzl, K; Reehuis, M; Miyasaka, S; Fujioka, F; Tokura, Y; Keimer, B; McIntyre, GJ; Ulrich, C
    Not available
  • Thumbnail Image
    Item
    Investigations of the magnetic and crystal field excitations in orthorhombically distorted perovskites RVO3 (R=Dy, Tb, Pr, Ce)
    (Australian Institute of Physics, 2017-01-31) O'Brien, J; Reynolds, NM; Mole, RA; Rovillain, P; Danilkin, SA; Schmalzl, K; Reehuis, M; Miyasaka, S; Fujioka, F; Tokura, Y; Keimer, B; McIntyre, GJ; Ulrich, C
    Inelastic neutron scattering experiments have been performed on a series of vanadates, in particular DyVO3, TbVO3, PrVO3, and CeVO3, to categorise the crystal field and magnetic excitations. The vanadates are isostructural to the multiferroic manganites TbMnO3 and DyMnO3, with corner sharing, Jahn-Teller distorted VO6 octahedra (orthorhombic space group Pbnm). However, they posses a collinear C-type antiferromagnetic structure, instead of an incommensurate spin arrangement as in the manganites. In the vanadates, the antiferromagnetic order sets in below Neel temperatures of TN = 110 K to 124 K [1-5]. Using inelastic neutron scattering on single crystals we were able to determine the crystal field spectrum and spin wave dispersion relations independently. In order to determine the nature of the crystal field excitations of these materials and in order to understand how the magnetic and crystal field excitations influence one another, we have theoretically calculated the crystal field excitation spectrum. The results are compared to the crystal field and spin wave excitations in the multiferroic maganites [6], in order to obtain a deeper understanding of the coupling mechanism between the rare earth elements and the transition metals in RVO3 and RMnO3, respectively.
  • Thumbnail Image
    Item
    Magnetically driven electric polarization in frustrated magnetic oxide multiferroics
    (Australian Institute of Physics, 2014-02-04) Narayanan, N; Reynolds, NM; Li, F; Mulders, AM; Rovillian, P; Ulrich, C; Bartkowiak, M; Hester, JR; McIntyre, GJ; Hutchinson, WD
    In multiferroics more than one ferroic order can coexist and in the present case we are interested in systems which exhibit simultaneous magnetic ordering and electric polarization (EP). Of particular interest are frustrated magnetic materials that exhibit an electric polarization that is strongly coupled to the magnetism [1]. Examples of such multiferroics are RMnO3 (R= Tb, Dy), Ni3V2O8, and RbFe(MoO4)2 [2-4]. This coupling can be utilized in applications such as magnetoelectric random access memory. Although technically relevant, the coupling mechanism between these two orders is complicated [1]. Whereas the magnetic ordering results from exchange interaction of unpaired spins, origins of EP coupled to the magnetic ordering depends on the interplay between lattice, orbital, spin and charge degrees of freedom. Several mechanisms such as the inverse Dzyaloshinskii-Moriya interaction, magnetostriction and coupling of the chirality to the crystal structure or a combination of them are currently discussed depending on the compound [2-5]. Additionally EP has ionic and electronic contributions. In the present work we investigate the coupling of magnetism to EP involving all three above mechanisms, in orthorhombic DyMnO3 (DMO), Cu3Nb2O8 and Ba3NiNb2O9 with neutron powder diffraction (NPD), magnetization and heat capacity measurements focusing on the magnetic and multiferroic phase transitions. In order to investigate the role of the lattice distortion or equivalently the role of oxygen, isotope substitution of 16O with 18O was performed on DMO. All samples are prepared as single phases via the solid state route and NPD experiments are carried out at Wombat and at Echidna at OPAL.
  • Thumbnail Image
    Item
    Magnetically driven electric polarization in frustrated magnetic oxide multiferroics
    (Australian Institute of Physics, 2014-02-06) Narayanan, N; Reynolds, NM; Li, F; Mulders, AM; Rovillain, P; Ulrich, C; Bartkowiak, M; Hester, JR; McIntyre, GJ; Hutchison, WD
    In multiferroics more than one ferroic order can coexist and in the present case we are interested in systems which exhibit simultaneous magnetic ordering and electric polarization (EP). Of particular interest are frustrated magnetic materials that exhibit an electric polarization that is strongly coupled to the magnetism [1]. Examples of such multiferroics are RMnO3 (R= Tb, Dy), Ni3V2O8, and RbFe(MoO4)2 [2-4]. This coupling can be utilized in applications such as magnetoelectric random access memory. Although technically relevant, the coupling mechanism between these two orders is complicated [1]. Whereas the magnetic ordering results from exchange interaction of unpaired spins, origins of EP coupled to the magnetic ordering depends on the interplay between lattice, orbital, spin and charge degrees of freedom. Several mechanisms such as the inverse Dzyaloshinskii - Moriya interaction, magnetostriction and coupling of the chirality to the crystal structure or a combination of them are currently discussed depending on the compound [2-5]. Additionally EP has ionic and electronic contributions. In the present work we investigate the coupling of magnetism to EP involving all three above mechanisms, in orthorhombic DyMnO3 (DMO), Cu3Nb2O8 and Ba3NiNb2O9 with neutron powder diffraction (NPD), magnetization and heat capacity measurements focusing on the magnetic and multiferroic phase transitions. In order to investigate the role of the lattice distortion or equivalently the role of oxygen, isotope substitution of 16O with 18O was performed on DMO. All samples are prepared as single phases via the solid state route and NPD experiments are carried out at Wombat and at Echidna at OPAL