Phonon Raman scattering of perovskite LaNiO3 thin films

We report an investigation of perovskite-type LaNiO3 thin films by Raman scattering in both various scattering configurations and as a function of temperature. The room-temperature Raman spectra and the associated phonon mode assignment provide reference data for phonon calculations and for the use of Raman scattering for structural investigations of LaNiO3, namely the effect of strain in thin films or heterostructures. The temperature-dependent Raman spectra from 80 to 900 K are characterized by the softening of the rotational A1g mode, which suggest a decreasing rhombohedral distortion towards the ideal cubic structure with increasing temperature

Raman scattering investigation across the magnetic and MI transition in rare earth nickelate RNiO3 (R = Sm, Nd) thin films

We report a temperature-dependent Raman scattering investigation of thin film rare earth nickelates SmNiO3, NdNiO3 and Sm0.60Nd0.40NiO3, which present a metal-to-insulator (MI) transition at TMI and an antiferromagnetic-paramagnetic Neel transition at TN. Our results provide evidence that all investigated samples present a structural phase transition at TMI but the Raman signature across TMI is significantly different for NdNiO3 (TMI = TN) compared to SmNiO3 and Sm0.60Nd0.40NiO3 (TMI =/ TN). It is namely observed that the paramagnetic-insulator phase (TN < T < TMI) in SmNiO3 and Sm0.60Nd0.40NiO3 is characterized by a pronounced softening of one particular phonon band around 420 cm-1. This signature is unusual and points to an important and continuous change in the distortion of NiO6 octahedra (thus the Ni-O bonding) which stabilizes upon cooling at the magnetic transition. The observed behaviour might well be a general feature for all rare earth nickelates with TMI =/ TN and illustrates intriguing coupling mechanism in the TMI > T > TN regime.Comment: Revised & published versio

L'extension de la forêt méditerranéenne : une réalité confirmée par les inventaires

Mesure des évolutions de la forêt méditerranéenne selon 2 ou 3 cycles d'inventaire et analyse et compare les données avec d'autres régions françaises

I.B.S. coatings on large substrates: Towards an improvement of the mechanical and optical performances

présenté par A. RemillieuxLarge mirrors (350 mm), having extremely low optical loss (absorption, scattering, wavefront) were coated for the VIRGO interferometer. The new mirror generation needs better wavefront and lower mechanical loss. The first results are discussed

Original optical metrologies of large components

présentée par A. RemillieuxThe coating deposition on large optical components (diameter 350 mm) has required the development of new metrology tools at 1064 nm. To give realistic values of the optical performances, the whole surface of the component needs to be scanned. Our scatterometer (commercial system) has been upgraded to support large and heavy samples. The other metrology tools are prototypes we have developed. We can mention the absorption (photothermal effect) and birefringence bench, a control interferometer equipped with an original stitching option, the optical profilometer (RMS roughness and small defect measurements). A detailed description of these metrology benches will be exposed. Their sensitivity, accuracy and capability to map the optical properties of substrates or mirrors will be discussed. We will describe the recent developments: the stitching option adapted to the Micromap profilometer to measure the RMS roughness on larger area (exploration of a new spatial frequency domain), the accurate bulk absorption calibration

A hysteresis model with dipole interaction: one more devil-staircase

Magnetic properties of 2D systems of magnetic nanoobjects (2D regular lattices of the magnetic nanoparticles or magnetic nanostripes) are considered. The analytical calculation of the hysteresis curve of the system with interaction between nanoobjects is provided. It is shown that during the magnetization reversal system passes through a number of metastable states. The kinetic problem of the magnetization reversal was solved for three models. The following results have been obtained. 1) For 1D system (T=0) with the long-range interaction with the energy proportional to $r^{-p}$, the staircase-like shape of the magnetization curve has self-similar character. The nature of the steps is determined by interplay of the interparticle interaction and coercivity of the single nanoparticle. 2) The influence of the thermal fluctuations on the kinetic process was examined in the framework of the nearest-neighbor interaction model. The thermal fluctuations lead to the additional splitting of the steps on the magnetization curve. 3) The magnetization curve for system with interaction and coercivity dispersion was calculated in mean field approximation. The simple method to experimentally distinguish the influence of interaction and coercivity dispersion on the magnetization curve is suggested.Comment: 22 pages, 8 figure

La fragilité des espaces ruraux : représentations, méthodes d'approche

The objective of this thesis project is the definitions of the social and economic development of fragile rural areas. The goal is to show that the definition of fragility given by those in charge of developing these areas is not unique. Inhabitants of the so-called fragile rural areas have other definitions based on their practices and their experience. Using this different image, it is possible to propose a new approach that can be the basis for a diagnostic method. / Les représentations du développement économique et social des espaces ruraux fragiles constituent l'objet de ce travail de thèse. Son but est de montrer que la fragilité des espaces telle que la caractérisent ceux qui ont en charge le développement et l'aménagement du territoire n'est pas la seule représentation possible. Les acteurs qui vivent dans ces espaces ruraux dits fagiles ont d'autres représentations fondées sur leurs pratiques de l'espace et leur propre expérience du développement. A partir de cette image différente des espaces fragiles, il est possible de proposer une nouvelle approche sur laquelle fonder une méthode de diagnostic

L'extension de la forêt méditerranéenne : une réalité confirmée par les inventaires

International audienceMesure des évolutions de la forêt méditerranéenne selon 2 ou 3 cycles d'inventaire et analyse et compare les données avec d'autres régions françaises

Physical and structural studies of chemical Vapor deposited lacunar neodymium manganite thin films

Lacunar Nd1-xMnO3-δ thin films were successfully deposited by a liquid source metal-organic MOCVD technique on (001) SrTiO3 (STO), LaAlO3 (LAO) and Si substrates. Optimal growth conditions are reported. TEM and X-ray diffraction characterisations reveal that the thin films grown on STO and LAO substrates are single crystalline layers epitaxially grown on the top of the substrates. The relationship between the crystallographic orientation of the films and those of the substrates were determined. Magnetic transition temperatures (Tc) of the as-grown STO films, deduced from Squid Magnetometer measurements, are compared to the corresponding bulk values (typically 100K). Our magnetic measurements also suggest a complicated magnetic behavior close to the one observed in bulk samples: magnetization curves obtained under different applied magnetic fields indicate a possible reverse of the magnetization sign at low temperatures

Physical and structural studies of chemical Vapor deposited lacunar neodymium manganite thin films

Lacunar Nd1-xMnO3-δ thin films were successfully deposited by a liquid source metal-organic MOCVD technique on (001) SrTiO3 (STO), LaAlO3 (LAO) and Si substrates. Optimal growth conditions are reported. TEM and X-ray diffraction characterisations reveal that the thin films grown on STO and LAO substrates are single crystalline layers epitaxially grown on the top of the substrates. The relationship between the crystallographic orientation of the films and those of the substrates were determined. Magnetic transition temperatures (Tc) of the as-grown STO films, deduced from Squid Magnetometer measurements, are compared to the corresponding bulk values (typically 100K). Our magnetic measurements also suggest a complicated magnetic behavior close to the one observed in bulk samples: magnetization curves obtained under different applied magnetic fields indicate a possible reverse of the magnetization sign at low temperatures