Papers by Luigi Paolasini
Journal of Applied Physics, 2014
The dynamics of a multiferroic domain wall in which an electric field can couple to the magnetiza... more The dynamics of a multiferroic domain wall in which an electric field can couple to the magnetization via inhomogeneous magnetoelectric interaction is investigated by the collective-coordinate framework. We show how the electric field is capable of delaying the onset of the Walker breakdown of the domain wall motion, leading to a significant enhancement of the maximum wall velocity. Moreover, we show that in the stationary regime the chirality of the domain wall can be efficiently reversed when the electric field is applied along the direction of the magnetic field. These characteristics suggest that the multiferroic domain wall may provide a new prospective means to design faster and low-power-consumption domain wall devices.
Collection SFN, 2014
The aim of these notes is to introduce the experimental methods and theoretical works in the doma... more The aim of these notes is to introduce the experimental methods and theoretical works in the domain of magnetic and resonant x-rays scattering on single crystals to investigate the electronic and magnetic long range order in strongly correlated electron systems. We highlight the role of the x-rays polarization analysis and control to determine the magnetic structure of materials and, more generally, the electronic long range order parameters responsible for the phase transitions.
Journal of Physics: Condensed Matter, 1993
... printed in the UK Magnetization density in heavy-fermion UPdZAl3 L Paolasinitz, JA PaixFiosT(... more ... printed in the UK Magnetization density in heavy-fermion UPdZAl3 L Paolasinitz, JA PaixFiosT(.GH Landert, A Delapalme§, N Satoli and T Komatsubad t Commission of the European Communities. ... Page 4. Magnetization densiry in heavy-fermion UPdz Alj 8907 2.4 [ 4 I I I I I 2.2 ...
Http Www Theses Fr, 1996
L'etude des proprietes magnetiques par diffusion inelastique et elastique de neutrons a ete r... more L'etude des proprietes magnetiques par diffusion inelastique et elastique de neutrons a ete realise sur deux composes intermetalliques de l'uranium: ufe#2 et upd#2al#3. La dynamique des ondes de spin a ete etudiee par diffusion inelastique de neutrons sur le ferromagnetique itinerant ufe#2 (t#c=165k). On a observe une seule onde de spin associee a la precession en phase des spins des atomes du fer, compare aux trois modes a faible energie prevus par le modele lineaire des ondes de spin, valable pour les composes isomorphes des terres rares rfe#2. Un regime hydrodynamique de type diffusif se manifeste autour de la temperature de transition et la valeur de sa constante de raideur depasse celle calculee pour les rfe#2 et le fer pur. Un fort amortissement de la branche acoustique des phonons transverses confirme les mesures des constantes elastiques par la methode ultrasonique. Les etudes par diffusion elastique de neutrons sur le fermion lourd supraconducteur upd#2al#3 (t#c=2k) sont centrees sur les proprietes magnetiques de l'etat normal de ce compose. Les mesures par diffusion de neutrons polarises nous ont permis de determiner la densite d'aimantation dans l'etat paramagnetique et de calculer par l'approximation dipolaire les contributions du moment orbital et de spin des electrons 5f de l'uranium. La structure magnetique a ete determinee par diffraction elastique de neutrons non polarises dans l'etat antiferromagnetique (t#n=15k). La dependance des intensites magnetiques en fonction d'un champ applique dans le plan d'anisotropie nous a permis de determiner l'orientation des moments magnetiques et d'interpreter le diagramme de phase, propose dans la litterature, comme un effet de reorientation des domaines magnetiques. Le dernier chapitre, contenant toute une serie d'experiences sur deux monocristaux de composition nominale differentes, se veut le point de depart de futures etudes sur la structure cristallographique et morphologique des defauts observes dans ces cristaux
Reflets de la physique, 2013
Synchrotron Radiation, 2014
Hard X-rays magnetic scattering takes advantage of the characteristic properties of X-ray beams a... more Hard X-rays magnetic scattering takes advantage of the characteristic properties of X-ray beams at third generation synchrotron radiation facilities: tuneable photon energy, controllable polarization and polarization analysis, excellent stability and brilliance. The aim of this lecture is to review the experimental and theoretical works in the domain of magnetic non-resonant and resonant X-ray diffraction on single crystals and thin films to investigate the electronic and magnetic long range order in strongly correlated electron systems. A general introduction to the theoretical aspects of the interaction between polarized photons and electrons will be given, with special emphasis to the description of the experimental polarized X-ray scattering methods to measure the relevant physical parameters.
Lecture Notes in Physics, 2006
... Dichroism and, in particular, x-ray magnetic circular dichroism (XMCD) is well described in t... more ... Dichroism and, in particular, x-ray magnetic circular dichroism (XMCD) is well described in the present book (see the chapters by A. Yaresko and G. van der Laan) as well as in the previous Mittelwihr proceedings (see various contributions in [17] and in particular the one by J.-M ...
Physica B: Condensed Matter, 1997
The magnetization densities and the uranium form factors of the two compounds UNiGa (metamagnetic... more The magnetization densities and the uranium form factors of the two compounds UNiGa (metamagnetic) and UNiAl (antiferromagnetic) have been determined by polarized neutron scattering. Both compounds crystallize in the noncentrosymmetric hexagonal space group P62m. Two methods have been applied to analyze the flipping ratios: a direct least squares atomic model refinement, and the noncentrosymmetric maximum entropy Fourier inversion. Both methods
Journal of Physics: Condensed Matter, 1999
A magnetization density study by means of polarized-neutron scattering on the intermetallic compo... more A magnetization density study by means of polarized-neutron scattering on the intermetallic compound 0953-8984/11/9/008/img12 is reported. 0953-8984/11/9/008/img12 belongs to the large 0953-8984/11/9/008/img14 (An = U, Np, Pu, Am; T = transition metal; X = In, Sn) family of compounds crystallizing in an ordered variant of the tetragonal 0953-8984/11/9/008/img15 type of structure (space group 0953-8984/11/9/008/img16). 0953-8984/11/9/008/img12 does not order magnetically but has a large magnetic susceptibility that qualifies it as an enhanced paramagnet or spin fluctuator. We report single-crystal magnetization measurements that show a significant magnetic anisotropy, with a c-axis susceptibility exceeding that measured on the basal plane by a factor of four. The magnetization density distribution in the unit cell was measured at 2 K by polarized-neutron scattering under a magnetic field of 5.5 T applied parallel to the c-axis. It was found that the major contribution to the magnetic susceptibility is located on the U atoms 0953-8984/11/9/008/img18 but a small response from the Co atoms is also measured 0953-8984/11/9/008/img19.
Magnetic resonant x-ray scattering experiments have been performed on a single crystal of EuFe 2 ... more Magnetic resonant x-ray scattering experiments have been performed on a single crystal of EuFe 2 As 2 at the Eu L 3 absorption edge. The orientation of Eu magnetic moments was directly determined: in the antiferromagnetic ordered phase they lay parallel to the crystallographic aaxis. In addition, non-resonant magnetic x-ray measurements indicate that Fe magnetic moments are aligned along the same direction in the spin density wave phase. As deduced by temperature dependence of integrated intensities, the Fe magnetic arrangement seems to be insensitive to the onset of Eu AFM phase. Some speculations on the low temperature space group are reported on the base of detected resonant reflections on forbidden Bragg positions.
École thématique de la Société Française de la Neutronique, 2014
The aim of these notes is to introduce the experimental methods and theoretical works in the doma... more The aim of these notes is to introduce the experimental methods and theoretical works in the domain of magnetic and resonant x-rays scattering on single crystals to investigate the electronic and magnetic long range order in strongly correlated electron systems. We highlight the role of the x-rays polarization analysis and control to determine the magnetic structure of materials and, more generally, the electronic long range order parameters responsible for the phase transitions.
Physical Review B, 2005
We have carried out resonant x-ray scattering experiments on NdNiO 3 single crystals aiming at th... more We have carried out resonant x-ray scattering experiments on NdNiO 3 single crystals aiming at the observation of a predicted orbital ordering that may explain the presence of an antiferromagnetic ordering with unusual modulation wave vector, q = ͑ 1 2 ,0, 1 2 ͒. A first-order structural phase transition has been observed at T MI = 200 K although no new superlattice peaks are present at this q position. Our experiment thus rules out the presence of an orbital ordering with this modulation. It rather seems that the magnetic, as well as the electronic, properties of this compound should be explained by introducing models of charge localization, either at the metal sites or at the ligand oxygen. We further comment on the observability of this charge ordering by resonant x-ray scattering.
International Union of Crystallography eBooks, Nov 16, 2022
2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2019
The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high tempera... more The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high temperatures by infrared spectroscopy combined with density functional perturbation theory calculations. The agreement between the measured phonon energies and widths with ab-initio calculated values provides a direct and pertinent test of the validity of advanced theoretical methods. Long observed anharmonic features in the infrared reflectivity find a clear explanation in terms of well-defined multiphonons scattering processes and lattice dynamics peculiarities, also responsible of a significant and sharp reduction of the longitudinal optical phonon lifetime at critical finite wave vectors. Our work highlights the importance of multi-phonons scattering processes on collective dynamics and related materials properties.
International Union of Crystallography eBooks, Nov 16, 2022
Systems with active orbital degrees of freedom can display collective excitations involving quadr... more Systems with active orbital degrees of freedom can display collective excitations involving quadrupoles and higher‐ rank multipoles, alone or in combination with dipoles. The identification and modelling of such propagating excitations, more complex than conventional magnetic spin‐waves, is important to get quantitative insight on multipolar two‐ion interactions, whose nature and form are poorly known. Indeed, whilst the static properties of multipolar-ordered systems provide only space-integrated information on the microscopic interactions between active multipoles, the dynamics of propagating modes depend on their detailed form. UO2 is one of the few systems where these phenomena have been experimentally investigated. This cubic insulator displays a first-order phase transition at 30.8 K to a non-collinear antiferromagnetic (AF) structure with a simultaneous electric-quadrupole ordering of the charge density [1]. Elementary excitations in the lattice originate from two meanfield m...
2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2019
The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high tempera... more The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high temperatures by infrared spectroscopy combined with density functional perturbation theory calculations. The agreement between the measured phonon energies and widths with ab-initio calculated values provides a direct and pertinent test of the validity of advanced theoretical methods. Long observed anharmonic features in the infrared reflectivity find a clear explanation in terms of well-defined multiphonons scattering processes and lattice dynamics peculiarities, also responsible of a significant and sharp reduction of the longitudinal optical phonon lifetime at critical finite wave vectors. Our work highlights the importance of multi-phonons scattering processes on collective dynamics and related materials properties.
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Papers by Luigi Paolasini