Browsing by Author "Sacuto, A"

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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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    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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    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.