PIEZOTRANSMISSION BEHAVIOR OF FERROMAGNETIC EuO UNDER MAGNETIC FIELD

Dans un précédent article, nous avons décrit le comportement du signal de piézotransmission de l'Oxyde d'Europium lorsque la température varie. Ce signal, [MATH] Tr/Tr, qui est directement relié au coefficient de pression de la transition optique observée change son signe à la temperature de Curie. Dans la région ferromagnétique la comparaison des mesures d'absorption et de piézotransmission met en évidence deux contributions du spectre "d'absorption apparente". Un faible champ magnétique supprime l'une d'elles. Les spectres de piézotransmission ont alors la même allure dans la région ferromagnétique H [MATH] Hs et dans la région paramagnétique. Cette forme est caractéristique d'une transition bande à bande. Les spectres d'absorption et de piézotransmission sont fortement influencés dans la région ferromagnétique, par la diffusion de la lumière due aux domaines magnétiques et doivent donc être analysés avec attention.It was reported in a previous paper that piezotransmission signal (ATr/Tr) changes its sign at the Curie temperature Tc. It can be shown that the piezotransmission signal is directly related to the pressure coefficient of the optical transition observed (4f 5d). Transmission and piezotransmission measurements have been carried out and in the ferromagnetic state on other contribution to the "apparent optical absorption" appears. Under a small magnetic field this other contribution disappears. Indeed the piezotransmission spectra have the same shape in the ferromagnetic state under a magnetic field than in the paramagnetic state. The shape is characteristic of a band to band transition. The piezotransmission and optical absorption in the ferromagnetic range are thus strongly influenced by light diffusion by domains and must be carefully analysed

Zeeman splittings of excitonic transitions at the Gamma point in wurtzite GaN: A magnetoreflectance investigation

International audienceWurtzite GaN on (0001) sapphire is studied by means of reflectance and magnetocircular dichroism up to 5.5 T at 2 K. This very powerful technique allows us to determine the Zeeman splittings to be about 0.05 meV/T for the X-A and X-C excitons and almost zero for the X-B exciton. Reflectance and dichroism are interpreted with a model of Gaussian dispersion of the excitonic energies and are in excellent agreement with previously proposed band-edge models

CONCENTRATION DEPENDENCE OF THE ZEEMAN SPLITTING OF EXCITON IN Zn1-xMnxTe AND Cd1-xMnxTe

Magnetoreflectivity and magnetization measurements were performed in Zn1-xMnxTe and Cd1-xMnxTe for 0.02 ≤x≤0.73 at 4.5 K in fields up to 5.5 T. Zeeman splitting versus average moment per cation is roughly linear for all x, but the slope decreases drastically at high x. A second-order perturbation calculation accounts for this decrease

APTITUDE A LA TRAITE MÉCANIQUE DES BREBIS DE RACE PRÉALPES DU SUD ET CROISÉES FRISONS × PRÉALPES; ÉTUDE A DIFFÉRENTS STADES DE LA LACTATION

International audienc

Hydrolysis of animall fats by lipase at temperatures below their melting points

We have studied the hydrolysis of high melting animal fats by the lipase from Candidarugosa at temperatures between 20°C and 37°C without the addition of surfactants or organic solvents. To establish the practical applications of this process we investigated the optimal conditions of the reaction at high substrate concentrations (50% fat w/v) to achieve 95% hydrolysis (or better) in 24 hours. Experiments were conducted in solid emulsions without constant stirring (500 ml total reaction volume). Under all conditions tested, edible pork lard was a better substrate than inedible beef tallow yielding up to 96% hydrolysis with as low as 0.3 g lipase/Kg fat or 98% hydrolysis with 0.5 g lipase/Kg fat. The optimum temperature for the hydrolysis of edible pork lard was around 30°C. Inedible beef tallow and pork lard did not exhibit a clear optimum temperature. Inedible lard gave results intermediate between those of edible lard and inedible beef tallow.Peer reviewe

Resonantly enhanced second harmonic generation in GaN-based photonic crystal slabs

International audienceThere is a major interest in fabricating III-nitride photonic structures for efficient nonlinear optical processes such as second-harmonic generation because they offer fairly large non linear coefficients and high optical damage thresholds. However, the use of III-nitrides has not been possible practically due to the high dispersion and the small birefringence for phase-matching. Recently, we have shown experimentally the enhancement of second-harmonic generation in epitaxial GaN-based photonic crystals [1]. By using calculated and experimental equifrequency surfaces, it is possible to identify the geometrical configurations that will allow quasi-phase matching to be satisfied and observed experimentally in the available wavelength tuning range of the laser. The second-harmonic field generated has been measured in reflection from the surface of photonic crystals etched into a GaN layer. A very large second-harmonic enhancement is observed when simultaneously the incident beam at the fundamental frequency ω excites a resonant Bloch mode and the second-harmonic field generated is coupled into a resonant Bloch mode at 2ω