Browsing by Author "Rovillain, P"

Now showing 1 - 16 of 16
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    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
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    Comparison of the magnetic and crystal field excitations in orthorhombically distorted vanadates and multiferroic manganites
    (Australian Institute of Nuclear Science and Engineering, 2012-11-15) Reynolds, N; Rovillain, P; Narayanan, N; Fujioka, F; Tokura, Y; Danilkin, SA; Mulders, AM; McIntyre, GJ; Ulrich, C
    Magnetism and ferroelectricity are both exciting physical properties and are used in everyday life in sensors and data storage. In multiferroic materials both properties coexist. They offer a great potential for future technological applications like the increase of data storage capacity or in novel senor applications. We have performed a comparative inelastic neutron scattering (INS) investigation on a series of vanadates, in particularly TbV0{sub 3} DyV0{sub 3}, PrV0{sub 3}, and CeV0{sub 3}, with their multiferroic Mn-counterparts. The Vanadates are isostructural to the multiferroic materials TbMnO{sub 3} and DyMn0{sub 3}, but posses a collinear antiferromagnetic spin arrangement below TN ≈110 K instead of a cycloidal spin structure below TFE 28 ≈K. By using inelastic neutron scattering we have obtained the spin wave dispersion relation and the crystal field excitations of the V-sublattice and the rare earth ions, respectively. The data will be compared with previously obtained INS data of D. Senff on TbMnO{sub 3} and our INS data on DyMnO{sub 3} with the intention of uncovering information about the complex interplay between the magnetic moments of the rare earth ions its role in the formation of the multiferroic phase.
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    Crafting the magnonic and spintronic response of BiFeO3 films by epitaxial strain
    (Nature Publishing Group, 2013-04-28) Sando, D; Agbelele, A; Rahmedov, D; Liu, J; Rovillain, P; Toulouse, C; Infante, IC; Pyatakov, AP; Fusil, S; Jacquet, E; Carrétéro, C; Deranlot, C; Lisenkov, S; Wang, D; Le Breton, JM; Cazayous, M; Sacuto, A; Juraszek, J; Zvezdin, AK; Bellaiche, L; Dkhil, B; Barthélémy, A; Bibes, M
    Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property—antiferromagnetism—has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mössbauer and Raman spectroscopies combined with Landau–Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves. © 2013, Nature Publishing Group.
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    Effects of 18O isotope substitution in multiferroic RMnO3 (R = Tb, Dy)
    (Australian Institute of Physics, 2016-02-05) Graham, PJ; Narayanan, N; McIntyre, GJ; Hutchison, WD; Ulrich, C; Reynolds, N; Rovillain, P; Hester, JR; Kimpton, JA; Yethiraj, M; Pomjakushina, E; Condor, K; Kenzelmann, M
    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. 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 in the b direction. The Pbnm space group is centrosymmetric and therefore does not allow ferroelectricity via atomic displacements, however our Reitveld analysis for the subgroup P21 shows significant displacements and polarisation along b that is comparable to the experimental value, making it the most promising candidate for ionic displacement induced polarisation in DyMnO3. These combined results demonstrate that structure is an important consideration in the emergence of ferroelectricity in these materials.
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    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.
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    Electric control of spin wave modes at room temperature in BiFeO3
    (Australian Institute of Physics, 2012-02-01) Rovillain, P; de Sousa, R; Gallais, Y; Sacuto, A; Measson, MA; Colson, D; Forget, A; Bibes, M; Barthélémy, A; Cazayous, M
    Multiferroic materials present the rare case to exhibit simultaneously magnetic and ferroelectric orders in interaction. This interaction corresponds to the magnetoelectric coupling. Thereby, magnetoelectric materials can potentially be used to control spins by an external electric field. This feature seems promising in spintronics and in magnonics that use magnetic excitations (spin wave) for information processing. In BiFeO3, a room-temperature magnetoelectric material, the interaction between the ferroelectric and magnetic orders offers the opportunity to control spins with an electric field. We have detected by Raman scattering two species of spin propagation modes (magnon) in BiFeO3 single crystal: in-plane (phi mode) and modes out of the cycloidal plane (psi mode) [1,2]. The frequencies of these modes have been successfully compared to the results of a Ginzburg-Landau mode [3]. Our result shows that the magnon modes might be interpreted as electromagnon. In order to characterize the magnetoelectric coupling, an external electric field has been applied. We show that in BiFeO3, the spin-wave frequency can be tuned electrically by over 30%, in a non-volatile way and with virtually no power dissipation [4]. These results showed that BiFeO3 is a very promising material for the generation and the control of spin waves in the future magnonic devices.
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    Electromagnon and phonon excitations in multiferroic TbMnO3
    (Americal Physical Society, 2012-07-30) Rovillain, P; Liu, J; Cazayous, M; Gallais, Y; Measson, MA; Sakata, H; Sacuto, A
    We have performed Raman measurements on a TbMnO3 single crystal under magnetic field along the three crystallographic directions. The flip of the spin spiral plane creates an electromagnon excitation. In addition to the electromagnons induced by the Heisenberg coupling, we have detected the electromagnon created by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified all the vibrational modes of TbMnO3. Their temperature dependencies show that only one phonon observed along the polarization axis is sensitive to the ferroelectric transition. This mode is tied to the Tb3+ ion displacements that contribute to the ferroelectric polarization. © 2012, American Physical Society.
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    Electromagnons in multiferroics probed by Raman light scattering comparison to neutron scattering investigations
    (Australian Institute of Nuclear Science and Engineering, 2012-11-15) Rovillain, P; Graham, PJ; Reynolds, N; Narayanan, N; Gallis, Y; Sacuto, A; Measson, MA; Sakata, H; McIntyre, GJ; Mulders, AM; Ulrich, C; Cazayous, M
    In multiferroic materials the two antagonistic effects, magnetic and ferroelectric orders, exist simultaneously. The switching of these orders is known as magnetoelectric coupling. Thereby, magnetoelectric materials can potentially be used to control spins or electric polarization with the application of an external electric or magnetic field, respectively. This makes them promising candidates for applications in spintronics or magnonics that use magnetic excitations for information processing. BiFe03, is the rare case where both orders coexist at room temperature. Using Raman scattering, we show that in BiFe03 the spin-wave energy can be tuned electrically by over 30%, in a non-volatile way with virtually no power dissipation. In TbMnO3 (and RMn2O5) the coupling of the orders gives rise to a hybrid excitation: the electromagnon. Electromagnons are spin wave excitations which possess an electric dipole. We have identified the magnetic excitation underneath the electromagnon by comparison with neutron measurement and further the phonon mode at the origin of the dipole activity. We have extended our investigations to Raman scattering and inelastic neutron scattering on DyMn03. The combination of both techniques offers the opportunity to obtain more information on the electromagnetic interaction in this type of multiferroic material.
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    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
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    Investigations into the magnetic and crystal field excitations of the orthorhombically distorted perovskites TbVO3 and CeVO3
    (Australian Institute of Physics, 2018-01-30) O'Brien, J; Reynolds, N; Rovillain, P; Danilkin, SA; Schmalzl, K; Reehuis, M; Mole, RA; 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 TbVO3 and CeVO3, to categorise the crystal field and magnetic excitations. The vanadates possess a configuration with corner sharing, distorted VO6 octahedra (space group Pbnm) with a collinear C-type antiferromagnetic structure occurring below Néel temperatures of TN = 110 K and 124 K respectively. Data from neutron scattering experiments reveal a hitherto unobserved shift of crystal field excitation energy in TbVO3 and CeVO3. Point-charge model calculations have confirmed this shift by theoretically calculating the crystal field excitation spectrum. We propose that the mechanism behind the effect is the onset of local magnetism caused by the ordering of the vanadium sublattice at the magnetic phase transition. This magnetic exchange field from the vanadium ions polarises the spins of the rare-earth ions located at the centre of the unit cell. This results in a Zeeman-like splitting of crystal field energy levels. As a result, crystal field transition energies demonstrate a linear shift as a function of internal magnetic field strength.
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    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.
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    Lattice and spin excitations in multiferroic h-YbMnO3
    (American Physical Society, 2012-11-09) Liu, J; Toulouse, C; Rovillain, P; Cazayous, M; Gallais, Y; Measson, MA; Lee, N; Cheong, SW; Sacuto, A
    Lattice and spin excitations have been studied by Raman scattering in hexagonal YbMnO3 single crystals. The temperature dependences of the phonon modes show that the E-2 mode at 256 cm(-1) related to the displacement of Mn and O ions in a-b plane is coupled to the spin order. The A(1) phonon mode at 678 cm(-1) presents a soft mode behavior at the Neel temperature. Connected to the motion of the apical oxygen ions along the c direction, this mode controls directly the Mn-Mn interactions between adjacent Mn planes and the superexchange path. Crystal field and magnon mode excitations have been identified. The temperature investigation of the spin excitations shows that the spin structure is strongly influenced by the Yb-Mn interaction. Under a magnetic field along the c axis, we have investigated the magnetic reordering and its impact on the spin excitations. © 2012, American Physical Society.
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    Lattice dynamics of multiferroic BiFeO3 studied by inelastic x-ray scattering
    (IOP Publishing Ltd., 2013-03-13) Borissenko, E; Goffinet, M; Bosak, A; Rovillain, P; Cazayous, M; Colson, D; Ghosez, P; Krisch, M
    We report an experimental study of the phonon dispersion in BiFeO3 single crystals at ambient conditions by inelastic x-ray scattering (IXS). The phonon dispersions were recorded along several symmetry directions up to 35 meV. Our results compare favorably with first-principles calculations performed using density functional theory (DFT) within the local-density approximation (LDA). We resolve a discrepancy concerning the symmetry of the optical phonon branches observed by Raman spectroscopy, determine the energy of the lowest Raman and infrared silent mode, and derive a subset of the elastic moduli of BiFeO3. © 2011 IOP Publishing LTD.
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    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
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    Magnetoelectric coupling in TbMnO3 explored via Raman spectroscopy
    (Australian Institute of Physics, 2013-02-06) Graham, PJ; Bartkowiak, M; Rovillain, P; Mulders, AM; Yethiraj, M; Pomjakushina, E; Conder, K; Kenzelmann, M; Ulrich, C
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    Subpicometer-scale atomic displacements and magnetic properties in the oxygen-isotope substituted multiferroic DyMn O3
    (American Physical Society, 2017-02-27) Narayanan, N; Graham, PJ; Reynolds, N; Li, F; Rovillain, P; Hester, JR; Kimpton, JA; Yethiraj, M; McIntyre, GJ; Hutchison, WD; Ulrich, C
    We have investigated DyMn16O3 and its isotopically substituted counterpart DyMn18O3 by neutron powder diffraction, x-ray diffraction, and heat capacity measurements to investigate the mechanism leading to its magnetically induced electric polarization. 18O isotope substitution does not influence the magnetic ordering temperature of the Mn ions TN,Mn or the multiferroic ordering temperature Tl coinciding with the onset of the spin spiral phase; however, it does reduce the ordering temperature of Dy into its incommensurate magnetic state TN,Dy from 7.0(1) K to 5.9(1) K. The temperature dependence of the magnetic propagation vector, qIC, changes with 18O substitution, while Tl remains almost constant, independent of qIC. Pronounced changes in the lattice parameters occur at the various phase transitions. Furthermore, distinct subpicometer-scale distortions of the MnO6 octahedra and displacements of the Dy ions are observed below the ferroelectric phase transition at Tl in both samples, pointing toward the mechanism for electric polarization and its coupling to the orbital degrees of freedom. ©2017 American Physical Society