Search

The origin of the effect of ``colossal magnetoresistance'' (CMR) remains still unexplained. In this work we revisit the spin dynamics of the pseudocubic ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ along the Mn-O-Mn bond direction at four $x$ doping values ($x\ensuremath{\le}0.5$) and various temperatures and report a lattice dynamics study at ${x}_{0}=0.2$, representative of optimal doping for CMR. We propose an interpretation of the spin dynamics in terms of orbital polarons. This picture is supported by the observation of a discrete magnetic energy spectrum ${E}_{n}^{\mathrm{mag}}(q)$ with $n$ levels, characteristic of the internal excitations of ``orbital polarons'' defined by ${\mathrm{Mn}}^{3+}$ neighbors surrounding a central ${\mathrm{Mn}}^{4+}$ hole. Because of its hopping, the hole mixes dynamically all the possible orbital configurations of its surrounding ${\mathrm{Mn}}^{3+}$ with degenerate energies. The ${E}_{n}^{\mathrm{mag}}$ values indicate a lifting of orbital degeneracy by phonon excitations. The $n$ value and the $q$ range are used to characterize these orbital polarons in direct space. At $x=0.125$ and $x=0.3$ the spectrum reveals two-dimensional polarons coupled by exchange and three-dimensional ``free'' polarons, respectively, with sizes $\ensuremath{\ell}=1.67a\ensuremath{\le}2a$ in all bond directions. At ${x}_{0}=0.2$, the spin and the lattice dynamics provide evidence for chains of orbital polarons of size $\ensuremath{\ell}=2a$ with a periodic distribution over $\ensuremath{\approx}3a$ and an interaction energy $\ensuremath{\approx}3$ meV. At $T\ensuremath{\le}{T}_{c}$ the charges propagate together with the longitudinal acoustic phonons along the chains enhancing their ferromagnetic character. The phase separation between metallic and ferromagnetic chains in a nonmetallic matrix may be crucial for CMR.

Nous rapportons 4 cas de mosaique ou chimere erythropoietique, decouverts dans diverses circonstances : etudes de double-population (DP) non transfusionnelle, d’antigene (Ag) faible ou de phenotype rare. Donneur n o 1 : DP pour les Ag RH1 et RH2. L’etude moleculaire montre la presence d’un gene RHD et des polymorphismes correspondant aux Ag RH2 et RH4, sans articularite ⇒ mosaique R 1 r/−r. Donneur n o 2 : suspicion d’Ag KEL1 affaibli. L’etude serologique montre la presence de DP dans les systemes ABO, RH, KEL et MNS. Une etude fine des histogrammes de la puce a ADN HEA v1.2 Immucor revele des differences entre ce sujet et des sujets heterozygotes sans anomalie phenotypique ⇒ probable chimerisme gemellaire. Patient n o 1 : perte d’expression des Ag RH1 et RH2 entre 2011 et 2018. L’etude du gene RHD ne montre aucune particularite ; celle du gene RHCE par puce ADN wRHCE Immucor conclut a un phenotype RH:−2 et le sequencage revele des signaux faibles correspondant aux polymorphismes de l’antigene RH2 ⇒ mosaique R 1 r/−r. Patient n o 2 : demande de confirmation d’un phenotype rare RH:−1,2,−3,−4,5 (contexte de myelodysplasie, echantillons post-transfusionnels). L’etude du gene RHD montre la presence d’un allele RHD*Weak D type 2, classiquement associe a un allele RHCE*cE. L’analyse par puce du gene RHCE conclut RH:2,−3,4,5, mais le sequencage revele un signal faible au niveau du polymorphisme RH3 ⇒ probable mosaique R 2 r’/−r’. L’etude moleculaire permet de suspecter ou confirmer la presence de mosaique ou de chimere. La confrontation avec les donnees serologiques et/ou une etude attentive des donnees moleculaires brutes reste indispensable pour conclure les phenotypes.

Contexte Les besoins en CGR dont le phenotype etendu (FY1/FY2, JK1/JK2, MNS3/MNS4) ou elargi (LE1/LE2, LU1, etc.) est connu est en constante evolution, aussi bien pour un usage therapeutique que non therapeutique (panels d’hematies-tests). Ce phenotypage peut se faire a grande echelle au laboratoire de qualification biologique des dons (LQBD), en ciblant dans un but d’efficience le phenotype ABO (O, A, B), Rh/K (R o R o , R 1 R 1 , R 2 R 2 , rr ; KEL :−1), et l’origine ethnique. Le phenotype R o R o , present chez 50 % de la population d’origine Africaine vs 2 % chez les Europeens, permet par exemple de recruter de nouveaux donneurs FY :−1,−2 et surtout MNS :−3,−4, ce qui revet une importance capitale pour la prise en charge des patients drepanocytaires. Methodes Les phenotypes etendus et elargis ont ete realises sur automates PK7300 Beckman Coulter et IH1000 Bio-Rad au LQBD. Resultats De debut 2016 a fin 2018, plus de 190 000 donneurs ont ete phenotypes en etendu et 13 000 en elargi, ce qui represente l’une des plus grandes bases de donnees pour satisfaire les demandes nationales. Par exemple, sur les 39 nouveaux donneurs MNS :−3,−4 depistes au niveau national du 01/01/2016 au 31/12/2018, 14 (36 %) l’ont ete par le LQBD Nord, vs 4 (15 %) du 01/01/2014 au 31/12/2016. Conclusions Ce travail a permis de nettement renforcer le pool de donneurs de panels d’hematies-tests et le stock de sang rare de la BNSPR, en particulier MNS :−3,−4 pour lequel existe une forte tension au niveau national et europeen. Un phenotypage de masse MNS1/MNS2 est desormais planifie, la demande de CGR MNS :−1 etant soutenue pour les patients drepanocytaires ; ceci permettra egalement de depister les exceptionnels sujets MNS :−1,−2.

Chicken tracheal organ cultures (TOCs), comprising transverse sections of chick embryo trachea with beating cilia, have proved useful in the isolation of several respiratory viruses and as a viral assay system, using ciliostasis as the criterion for infection. A simple technique for the preparation of chicken tracheal organ cultures in glass test tubes, in which virus growth and ciliostasis can be readily observed, is described.

Chicken kidney (CK) cell cultures have historically proved useful for the assay of a number of viruses including coronaviruses. A technique for the preparation of such cell cultures, using a combination of manual and trypsin disaggregation of kidneys dissected from 2- to 3-week-old birds is described. This technique routinely gives high cell yield together with high viability and the resultant adherent primary cultures can be used for virus growth and plaque formation.

Chicken tracheal organ cultures (TOCs), comprising transverse sections of chick embryo trachea with beating cilia, have proved useful in the isolation of several respiratory viruses and as a viral assay system, using ciliostasis as the criterion for infection. A simple technique for the preparation of chicken tracheal organ cultures in glass test tubes, in which virus growth and ciliostasis can be readily observed, is described.

Le depistage de masse de phenotypes rares de type public negatif est problematique pour les laboratoires de qualification biologique des dons (QBD), les reactifs correspondants etant en quantite restreinte ou tres onereux. De nouveaux reactifs monoclonaux autorisent desormais cette approche sur automates a haute cadence. La collaboration entre divers intervenants (collecte, preparation, laboratoire de production d’anticorps monoclonaux, QBD, logistique, CNRGS) a permis de produire un reactif monoclonal anti-VEL1 (clone SpG213Dc3) et la mise au point d’un protocole d’utilisation sur automate PK7300. D’octobre 2015 a fin avril 2017, 981 650 dons ont ete testes (Ile-de-France, Nord de France, Normandie), permettant de depister 339 donneurs VEL : − 1, confirmes par le CNRGS au niveau phenotypique (deux sources de reactifs) et moleculaire (genotype VEL* − 01/VEL* − 01). La prevalence du phenotype VEL : − 1 calculee sur 494 792 sujets est de 6,1/104, IC 95 [5,5/104; 6,8/104], superieure a la valeur 4/104 couramment citee chez les Caucasiens (etablie sur seulement 10 000 individus). Ce travail a permis de considerablement renforcer le stock de CGR VEL : − 1 a la Banque nationale de sang de phenotype rare, tout en informant les nouveaux donneurs sur les precautions a prendre en cas de future transfusion. Une deuxieme etape consistera a etudier la fratrie des sujets depistes. Un essai de production d’anticorps monoclonal anti-CO1 a ete initie et d’autres reactifs seraient utiles a l’avenir, tels que anti-GE2, anti-KEL7, anti-RH18 et anti-RH34. De telles etudes de depistage de masse entrent dans une demarche de securite transfusionnelle et de sante publique, aussi bien au niveau national qu’international.

We detected two spontaneous precession frequencies in antiferromagnetic pure LaMnO3, the end member of different families of charge-doped manganites. The muon site and local field orientation are identified for one frequency, which provides a measure of the staggered magnetization. We present additional zero and longitudinal field muon relaxation data on an LaMnO3.045 sample in which a new regime appears above an intermediate temperatureT*, where regions of magnetic order coexist with domains of fluctuating moments. These results are discussed in terms of nucleation of the ordered phase in a superparamagnetic matrix.

Epitaxial Sm thin films and Sm/Y superlattices have been grown with a high single-crystal quality. The complex nine hexagonal close-packed planes stacking sequence has been successfully obtained in a 5000 \AA{}-thick film, whose magnetic behavior presents a long-range antiferromagnetic order of the hexagonal sites below 100 K, as in the bulk element. However, from neutron scattering, the relative magnetic and nuclear contributions indicate a significant enhancement of the magnetic moment compared to the bulk value. For the superlattice, the neutron-scattering results show neither long-range structural coherence of the stacking sequence along the c direction nor a coherent magnetic ordering at low temperatures.

We studied ${\mathrm{Mn}}_{12}$-acetate by inelastic neutron scattering and diffraction. We separated the energy levels corresponding to the splitting of the lowest $S$ multiplet ( $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}10$ ground state). The irregular spacing of the transition energies unambiguously shows the presence of high-order terms in the spin Hamiltonian [ $D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.457(2){\mathrm{cm}}^{\ensuremath{-}1}$, ${B}_{4}^{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2.33(4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{cm}}^{\ensuremath{-}1}$]. The relative intensity of the lowest energy peaks is very sensitive to the small transverse term that is responsible for quantum tunneling, providing the first determination of this term in zero magnetic field $[{B}_{4}^{4}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}3.0(5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{cm}}^{\ensuremath{-}1}]$.

Contexte Une nouvelle technique de phenotypage etendu pour la qualification biologique des dons utilise une gamme de reactifs prets a l’emploi (Diagast) pour la determination des antigenes Fya, Fyb, Jka, Jkb, S, s, sur automate a haute cadence PK7300 (Beckman-Coulter). But Evaluer les performances globales de la technique. Methode Deux mille trois cent cinquante-deux donneurs de phenotype etendu connu (gel filtration ou immunocapture) ont ete etudies. Les echantillons discordants avec l’anteriorite ont ete transmis au CNRGS pour des tests complementaires (phenotypage, biologie moleculaire). Resultats La cadence a ete estimee a 250 echantillons/heure. Tous les phenotypes Fya, Fyb, Jka, Jkb, S, s ont ete concordants, a l’exception de 18 cas pour l’antigene Fyb (negatif en technique gel ou immunocapture et positif/douteux sur PK7300). Ces 18 echantillons ont ete etudies en biologie moleculaire, avec une concordance observee de 100 % entre le PK7300 et la PCR : ils correspondent tous en effet au phenotype Fyx (expression affaiblie de Fyb due a la mutationc.265C>T dans l’allele FY*02). Deux donneurs ont montre un affaiblissement de l’antigene Jkb, confirme au CNRGS. Des tests de biologie moleculaire sont en cours pour en explorer l’origine. Conclusion Integree a la QBD, cette technique permet la realisation du phenotype etendu plus rapidement que les techniques habituelles de colonne-filtration ou d’immunocapture. Elle demontre par ailleurs une sensibilite accrue pour la detection du phenotype Fyx. Les resultats obtenus permettent de penser que cette methode est pertinente dans un programme de phenotypage de masse et qu’elle sera egalement une source importante de depistage de nouveaux donneurs de sang rare.

Elastic neutron scattering experiments, performed in semiconducting ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ single crystals $(x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.05,0.08)$, reveal new features in the problem of electronic phase separation and metal insulator transition. Below ${T}_{N}$, the observation of a broad magnetic modulation in the $q$-dependent elastic scattering intensity, centered at nearly identical ${q}_{m}$ whatever the $q$ direction, can be explained by a liquidlike spatial distribution of similar magnetic droplets. A semiquantitative description of their magnetic state, diameter, and average distance can be done. Such a picture can explain the anomalous characteristics of the spin wave branches previously observed.

The parent compound of the giant magnetoresistance Mn-perovskite, ${\mathrm{LaMnO}}_{3}$, has been studied by thermal analysis and high-resolution neutron-powder diffraction. The orthorhombic $\mathrm{Pbnm}$ structure at room temperature is characterized by an antiferrodistorsive orbital ordering due to the Jahn-Teller effect. This ordering is evidenced by the spatial distribution of the observed Mn-O bond lengths. ${\mathrm{LaMnO}}_{3}$ undergoes a structural phase transition at ${T}_{\mathrm{JT}}\ensuremath{\approx}750$ K, above which the orbital ordering disappears. There is no change in symmetry although the lattice becomes metrically cubic on the high-temperature side. The ${\mathrm{MnO}}_{6}$ octahedra become nearly regular above ${T}_{\mathrm{JT}}$ and the thermal parameter of oxygen atoms increases significantly. The observed average cubic lattice is probably the result of dynamic spatial fluctuations of the underlying orthorhombic distortion.

Magnetodynamics of ferrofluid γ-Fe2O3 nanoparticles is studied by Quasi-Elastic Neutron Scattering between 10 K and 250 K in the frequency range 1010–1012 Hz. We probe independently the precession of the core magnetic moment and surface spins fluctuations observed in a dissipative regime. These fluctuations slow down at low temperature leading to a frozen disorder of the surface layer.

Neutron diffraction experiments and macroscopic magnetization measurements show evidence of the stabilization of the helical magnetic phase over large temperature ranges for Tb and alloy films grown epitaxially on yttrium. In particular, the temperature of the transition between the helical and the ferromagnetic states is shifted from 220 K for bulk terbium to 160 K for a pure terbium film grown epitaxially on yttrium, despite the low stability of the helical phase in the bulk element. The decrease of the Curie temperature is due to the negative c-axis strain induced by the epitaxial growth on yttrium. The epitaxial strains also induce modifications of the Fermi surface, which leads to an increase of the turn angle even at . At low temperature, a long-wavelength-modulated phase, whose origin still remains to be explained, has been observed.

The Curie temperature of dysprosium films epitaxially grown on yttrium and on erbium is shown to increase continuously with the epitaxial strain induced along the c-axis. This variation is correlated to modifications of the α strains, of the γ distortion and of the exchange energy barrier. The evolution of these different terms is discussed from the experimental thermal variations of the lattice parameters and turn angles determined by neutron diffraction.

Low angle polarized neutron scattering experiments have been performed on an Er91 A/Fe39 A multilayer. The evolution of the intensity of the first peak with the temperature and the external magnetic field shows that the average magnetizations of Fe and Er layers are in the applied field direction. The study of the intensities of the second and the third peaks indicates that there is an interface effect: some erbium atoms remain antiferromagnetically coupled to iron at the interface.

The compound La0.875Sr0.125MnO3 exhibits a ferromagnetic phase below TC=181 K. At TO’O”=159 K, a magneto-structural transition occurs with spectacular properties. Extra Bragg peaks appear and, at related q-values, the spin-wave energies split and lock successively at the values of the different phonon modes. Moreover, in the long-wavelength range, two close spin-wave branches can be measured. They are characterized by two small gaps and similar stiffness constants. They have two distinct temperature behaviors. The lowest-energy branch seems to disappear at TO’O”.

The charge and magnetic states of LaMnO 3 single crystal with electron doping by Ce (7%) have been studied and compared with undoped manganite and a Sr-doped compound. Extensive study including investigation of magnetic, transport properties, infrared optical absorption, electron-spin resonance, and neutron scattering have been performed. The substitution of La by donor impurity of Ce results in a partial compensation of holes induced by cation vacancies. Results are explained by charge segregation and “modulated” canted antiferromagnetic state.

In the diagram of La 1− x Sr x MnO 3 the compound with x =0.125, exhibits, below T c =181 K, a ferromagnetic phase. At T O′O″ =159 K, a magneto-structural transition occurs with amazing properties. New superstructure Bragg peaks appear. At related q -values, the spin wave energies split and lock at the values of phonon modes. This suggests a complex ground state with mixed magneto-vibrational excitations.

Nous presentons une etude des excitations magnetiques dans des composes de La1−x Srx MnO3 et La1−x Cax MnO3 ou x varie de maniere a couvrir une large partie des diagrammes de phases. Dans l’etat antiferromagnetique, 0.1 0.15 ou x(Ca) > 0.22. Dans ces regions, les spectres d’ondes consiste en une dispersion quadratique a petit vecteur d’onde, et des niveaux a l’approche du bord de zone, caracteristiques de “defauts magnetiques” locaux. L’ensemble de ces anomalies pourrait s’expliquer par la mobilite de la paire de spins de Zener assistee par les phonons du reseau.

The magnetic properties of ${\text{BiCu}}_{2}{\text{PO}}_{6}$ have been analyzed by means of magnetic-susceptibility and inelastic neutron-scattering measurements on powder samples by evaluating the spin-exchange interactions on the basis of density-functional calculations and by simulating the inelastic neutron scattering in terms of spin-exchange parameters. ${\text{BiCu}}_{2}{\text{PO}}_{6}$ exhibits magnetic properties described by the two-leg spin ladder with strong spin frustration along each leg chain and has a gapped quantum singlet ground state with excited magnetic states, showing an incommensurate dispersion arising from frustration.

We used polarized inelastic neutron-scattering measurements to shed light on the spin-lattice quantum entanglement in multiferroic materials. We report an evidence for hybrid elementary excitations made of a mixing between spin waves and phonons, which can be considered as multiferroic Goldstone modes. We argue that the Dzyaloshinskii-Moriya interaction could be at the origin of this hybridization.

Polarization analysis of the transmitted beam was performed using a pulsed neutron source in a reentrant-spin-glass (RSG) system ${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$, for a concentration range (0.23\ensuremath{\le}x\ensuremath{\le}0.28) encompassing the critical concentration. The polarization P was measured as a function of temperature, neutron wavelength, and applied field. Unlike other RSG systems previously studied, P decreases at all temperatures below the Curie temperature even for the samples close to the critical concentration. This behavior is also observed in Fe-Zr alloys. In Ni-Mn the wavelength dependence of the polarization indicates the existence of magnetic domains, whose size \ensuremath{\delta} decreases, with increasing x, from 10 to 50 \ensuremath{\mu}m at x=0.23 to a few thousands of angstroms at x=0.25. No depolarization occurs for xg0.25. As shown for x=0.23, the irreversibilities of the polarization, which depend on the cooling conditions, indicate that the domain arrangement freezes at low temperature. Clearly, in Ni-Mn, the drop of the susceptibility at low temperature does not result from a decrease of the size or magnetization of the domains but from a slowing down of their mobility.

Amorphous Fe90−x Ni x Zr10 is a system that exhibits a relatively high degree of magnetic exchange frustration, which becomes stronger as the system approaches the composition of amorphous pure iron. Thus, while samples with moderate amounts of iron (x≥5) are ferromagnetic, the samples with the highest concentration of iron (x≤1) behave like reentrant spin glasses. We have performed a detailed neutron scattering study of the spin‐wave excitations in this system for x=1, 5, 10, 20. In all cases, well‐defined spin‐wave excitations were observed below a transition temperature T c that decreased from 455 K (for x=20) to 250 K (for x=1). For x=5, 10, 20 the spin‐wave stiffness coefficient follows the temperature dependence expected for a conventional ferromagnet but the spin‐wave excitations broaden considerably at low temperatures. For x=1 the spin‐wave stiffness coefficient softens at low temperatures and an elastic component of the scattering, associated with the development of a spin‐glass order parameter, appears below T≊0.28T c . A coexistence of propagating spin‐wave excitations and spin freezing phenomena is observed below this temperature down to T=0.09T c . These results are discussed in terms of the relevant current theories.

Inelastic neutron scattering has been used on La1−x Ca x MnO3 compound 0with 0≤x≤0.10 to describe their dynamic magnetic properties. In addition to super exchange coupling between Mn ions (ferromagnetic (F) in (a, b) planes and antiferromagnetic (AF) along the c direction), a new type of F coupling is found, induced by mobile carriers between magnetic Mn ions. It is revealed by well-defined propagative spin wave modes with a gap and a nearly isotropic dispersion law: ω=ω0+Dq 2. The q-evolution of the instantaneous spin pair correlations remind F inhomogeneities embedded in the mean AF lattice. These results could be understood in a frame of an electronic phase separation.

We have measured the magnetic excitations by inelastic neutron scattering in the paramagnetic phase down to $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, in ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, which remains spin liquid down to $0.05\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and in ${\mathrm{Tb}}_{2}{\mathrm{Sn}}_{2}{\mathrm{O}}_{7}$, which shows an ordered spin ice state below $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature dependence of the crystal field excitations, measured in the energy range $0\char21{}10\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$, shows striking differences between the two compounds. The neutron data were reasonably reproduced by a set of crystal field parameters, showing that while the two compounds have similar values of the gap between the first two crystal field doublets, the associated wave functions are exchanged. This difference comes from a change in sign of the crystal field parameter ${B}_{6}^{0}$. The neutron data also suggest that an excitation at very low energy (about $0.03\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$) is present in both compounds. Using these sets of crystal field parameters, the high field magnetization and low field susceptibility data can be correctly reproduced by taking the exchange interaction into account in the molecular field approximation. The values obtained for the exchange integral are discussed.

We have measured the spin-wave dispersion in the ferromagnetic metallic phase of five manganite compounds: ${\mathrm{La}}_{0.7}{({\mathrm{Ca}}_{1\ensuremath{-}y}{\mathrm{Sr}}_{y})}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ with $y=0$, 0.2, 0.4, and 1 and ${\mathrm{La}}_{0.8}{\mathrm{Sr}}_{0.2}\mathrm{Mn}{\mathrm{O}}_{3}$. An apparent broadening of the spin waves at the zone boundary in the [001] direction was observed, in agreement with previous work. Detailed investigation of this broadening by carefully separating lattice and magnetic contributions to the scattering cross section revealed that this observation is an artifact of the proximity of an optical phonon branch and the magnon branch. Upon separating out the magnon contribution, it becomes clear that the two branches are not strongly coupled and neither mix with nor damp each other within experimental uncertainty. Thus our experiment rules out significant magnon-phonon coupling. We also found that the softening of the spin-wave energy near the zone boundary appears in the manganites with low $(y=0)$ and high $(y=1)$ Curie temperatures regardless of their crystal structure. Thus it is not related to the existence of correlated polarons. Finally, we report the evolution of the magnetic couplings with doping throughout the whole phase diagram. To explain the observed continuity of the exchange component of the magnetic coupling measured in the metallic phase, we consider a possible persistence of dynamical orbital fluctuations reminiscent of orbital ordering, which occurs in the low-doping insulating regime.

Contexte Le phenotypage D est realise lors de qualification biologique des dons (QBD) sur automate PK7300 avec les reactifs Totem et HM10 (Diagast). Cette methode associant 2 anticorps en technique bromeline est reputee tres sensible et censee reconnaitre la plupart des D variants. Depuis 2005, les bonnes pratiques exigent la recherche du D faible chez les donneurs D-C+ et/ou E+ en test indirect a l’antiglobuline (TIA), en particulier si la technique de 1 ere intention ne depiste pas les variants DVI et D faible type 2. But Reevaluer la pertinence de la recherche du D faible chez les sujets D-C+ et/ou E+ ; etudier la nature/frequence des D variants non depistes avec les reactifs actuels de 1 re intention. Methode Neuf mille trois cent quarante-huit donneurs D-C+ et/ou E+ ont ete testes en TIA avec 2 reactifs anti-D : clones HM16 (Diagast) et ESD1 (Bio-Rad). Toute positivite avec au moins l’un des 2 reactifs a ete etudiee au CNRGS (genotypage RHD puce wRHD BioArray Immucor/sequencage). Resultats Cent trente donneurs (1,4 %) ont montre un TIA positif. Cent ont pu etre genotypes a ce jour et tous ont un D variant : DV type 7 (20 %), D faible type 38 (10 %), D faible type 2 (8 %), D faible type 11 (8 %), D (delEx10) (8 %), D faible type 15 (7 %), D faible type 56 (6 %), DVI (5 %), D faible type 1 (5 %), D faible type 5 (3 %), D faible type 16 (3 %), autres (17 %). Conclusion Certains sujets DVI et D faible type 2 et de nombreux autres D variants ne sont pas depistes en 1 re intention. Nos resultats confirment ainsi la necessite de poursuivre la recherche du D faible chez les donneurs D-C+ et/ou E+. Cette approche apparait par ailleurs « cout–efficace » par rapport au genotypage RHD systematique des donneurs D- propose dans certains pays.

Contexte L’expression des antigenes LE1 et LE2 depend des fucosyltransferases FUT2 (SE) et FUT3 (LE), en competition pour le meme substrat dans les cellules secretrices. Les actions de FUT2, puis de FUT3 forment LE2. Si FUT2 est alteree, alors FUT3 peut agir en premier, rendant l’ajout de fucose supplementaire impossible et LE1 est forme. Le phenotype LE:1,2 est possible si l’activite de FUT2 est reduite mais non abolie, cas frequent en Asie (mutation c.385A > T du gene FUT2 ) mais considere rare en Europe. Nous avons recu au CNRGS du site QBD de Lille un echantillon de donneur caucasien LE:W1,2 afin de confirmer ce phenotype et d’en rechercher la cause moleculaire. Methodes Phenotypage Lewis par anticorps monoclonaux en gel-filtration Bio-Rad et technique tube reactifs Diagast. Sequencage du gene FUT2 . Resultats Le phenotype Lewis etait confirme LE:W1,2 en limite de detection pour LE1. La sequence codante de FUT2 revelait la mutation c.379C > T; p.Arg127Cys sur la base d’un allele secreteur, associe a l’allele non-secreteur ( se 428 ) frequent dans la population caucasienne (45 %). Discussion En 1998, Liu et al. avaient considere l’allele Se 379 de FUT2 comme fonctionnel malgre une diminution de 60 % de l’activite de l’enzyme. Les resultats presentes ici montrent que cette mutation entraine un phenotype LE:W1,2. Des etudes d’exome effectuees chez plusieurs milliers de volontaires caucasiens indiquent une frequence allelique de 1 % de la mutation c.379C > T. Etant donne la prevalence de l’allele non-secreteur, on en deduit donc qu’au minimum 1 % des sujets caucasiens devraient presenter un phenotype LE:W1,2, la detection de cet antigene LE1 faible dependant toutefois du reactif utilise.

The parent compound of the giant magnetoresistance perovskite Mn-oxides, LaMnO3, has an orthorhombic Pbnm crystal structure at room temperature characterized by the presence of an anti-ferrodistorsive eg(1):eg(2) orbital ordering due to a cooperative Jahn-Teller effect. The compound undergoes a structural phase transition at TJT ≈ 790 K, above which the orbital ordering disappears. There is no change in symmetry, although the lattice becomes metrically cubic on the high-temperature side. The refinement of the crystal structure shows that MnO6 octahedra become much more regular above TJT and the thermal parameter of oxygen atoms increases significantly. The observed average cubic lattice is probably the result of dynamical spatial fluctuations of the underlying small orthorhombic distortion.

The structural and magnetic properties of Fe/Cr and Fe/Ag magnetic superlattices are discussed. The presence of antiferromagnetic coupling in Fe/Cr superlattices was clearly established, whereas Fe/Ag superlattices do not show antiferromagnetic coupling in their as-prepared state. Thermal annealing and ion irradiation lead to an increase of the magnetoresistance due to the formation of a granular FeAg alloy and a Kondo system, respectively.

International audience; The origin of the colossal magnetoresistance (CMR) observed in La1-xCaxMnO3, at x approximate to 0.3, is still largely debated. Actually, the precursor phase of the ferromagnetic ( F) metallic state, defined as the concentration ranges 0.125

By using nuclear magnetic resonance techniques we show that for T30 K the La0.875Sr0.125MnO3 compound displays a nonuniform charge distribution, comprised of two interconnected Mn ion subsystems with different spin, orbital, and charge couplings. The NMR results agree very well with the two spin wave stiffness constants observed at small q values in the spin wave dispersion curves [Phys. Rev. B 67, 214430 (2003)]. This picture is probably related to a yet undetermined charge and orbital superstructure occurring in the ferromagnetic insulating state of the La0.875Sr0.125MnO3 compound.

We study the spin dynamics of the manganites ${\mathrm{La}}_{0.9}{\mathrm{Ca}}_{0.1}\mathrm{Mn}{\mathrm{O}}_{3}$ and ${\mathrm{La}}_{0.91}{\mathrm{Sr}}_{0.09}\mathrm{Mn}{\mathrm{O}}_{3}$ in magnetic field. Previous studies in zero field have shown that the magnetic ground state is inhomogeneous with ferromagnetic $(F)$ droplets embedded in a canted antiferromagnetic (CAF) matrix. The spin dynamics consists of two spin wave branches in a high and a low-energy range, respectively. However, the assignment of these two branches either to a mean CAF medium or to $F$ droplets embedded in an AF matrix, was uncertain. The present study shows that these two branches do not follow the mean-field calculation for a homogeneous CAF state and do not correspond either to a phase separation between AF and $F$ states. The progressive spin-flop transitions observed for $H\ensuremath{\Vert}\mathbf{b}$ and $H\ensuremath{\Vert}\mathbf{a}+\mathbf{b}$, give rise to strong changes in the dispersion of the spin waves. The low-energy branch, only visible around $F$ zone centers at zero field, appears at any $q$-value in magnetic field. Moreover, as soon as the AF spin component deviates from its easy axis, leading to a decrease of the magnetic anisotropy, the high-energy branch is no more defined near the zone boundary. Its intensity is transferred to a higher flat level, likely related to defects in the CAF matrix. These new results strongly support a picture where these magnetic excitations arise from a modulated canted antiferromagnetic ground state consisting of two coupled $F$ and AF components.

The bilayer manganite La1.2Sr1.8Mn2O7 exhibits a phase transition from a paramagnetic insulating (PI) to a ferromagnetic metallic (FM) state with a colossal magnetoresistance (CMR) effect. Upon 60% Pr substitution, magnetic order and PI to FM transition are suppressed. Application of a moderate magnetic field restores an FM state with a CMR effect. Neutron scattering by a single crystal of (La0.4Pr0.6)1.2Sr1.8Mn2O7, under a magnetic field of 5 T, has revealed a long-range and homogeneous ferromagnetic order. In the PI phase, under zero field, correlated lattice polarons have been detected. At 28 K, under 5 T, the spin wave dispersion curve determines an in-plane isotropic spin wave stiffness constant of 146 meV A(2). So the magnetic field not only generates a homogeneous ferromagnetic ground state, but also restores a magnetic coupling characteristic of FM CMR manganites.

The bilayer manganite La1.2Sr1.8Mn2O7 exhibits a phase transition from a paramagnetic insulating (PI) to a ferromagnetic metallic (FM) state with a colossal magnetoresistance (CMR) effect. Upon 60% Pr substitution, magnetic order and PI to FM transition are suppressed. Application of a moderate magnetic field restores an FM state with a CMR effect. Neutron scattering by a single crystal of (La0.4Pr0.6)1.2Sr1.8Mn2O7, under a magnetic field of 5 T, has revealed a long-range and homogeneous ferromagnetic order. In the PI phase, under zero field, correlated lattice polarons have been detected. At 28 K, under 5 T, the spin wave dispersion curve determines an in-plane isotropic spin wave stiffness constant of 146 meV A(2). So the magnetic field not only generates a homogeneous ferromagnetic ground state, but also restores a magnetic coupling characteristic of FM CMR manganites.

We report a study of spin waves in ferromagnetic La1-xCaxMnO3, at concentrations x=0.17 and x=0.2 very close to the metallic transition (x=0.225). Below T(C), in the quasimetallic state (T=150 K), nearly q-independent energy levels are observed. They are characteristic of standing spin waves confined into finite-size ferromagnetic domains, defined only in the (a,b) plane for x=0.17, and in all directions for x=0.2. They allow an estimation of the domain's size, a few lattice spacings, and of the magnetic coupling constants inside the domains. These constants, anisotropic, are typical of an orbital-ordered state, allowing one to characterize the domains as "hole poor." The precursor state of the collossal magnetoresistance metallic phase appears, therefore, as an assembly of small orbital-ordered domains.

We present the evolution of the static and dynamic spin correlations in La 1-x Ca x MnO 3 and La 1-x Sr x MnO 3 compounds (x Ca ≤ 0.20, x Sr ≤ 0.125), studied by neutron scattering. We show that these systems evolve, at low temperature, from a canted antiferromagnetic state (CAF) towards an insulating ferromagnetic state (FI), approaching the metallic transition (x Ca =0.22 and x Sr = 0.17). For x Ca and x Sr < 0.125, we observe magnetic elastic diffuse scattering characteristic of a charge segregation, with interacting ferromagnetic (F), hole-rich platelets imbedded in a hole-poor matrix. Inelastic scattering reveals two spin wave branches related respectively to the dynamics of the two coupled magnetic media. One, which indicates an anisotropic superexchange coupling, is mainly related to the hole-poor matrix, while the other one, which indicates a ferromagnetic coupling, is mainly related to the (F) platelets, showing the same q-dependent intensity, x Ca = 0.125 is a limit case where the (CAF) state and the diffuse scattering disappear. In the compounds with x Ca = 0.20 and x Sr = 0.125, an intriguing insulating and ferromagnetic (FI) phase occurs at low temperature. The superstructure Bragg peaks at q o = (0, 0, 0.5)ortho, typical of this (FI) state, appear together with an unusual spin dynamics. At low q-values, (q < q o), the spin waves are characteristic of long range ferromagnetic coupling. At qo, a gap opens in the spin wave branch. There and beyond qo, up to the zone boundary, the energy-values of the magnetic excitations lock successively on the transverse acoustic, longitudinal acoustic and finally on the longitudinal optic phonon modes. This study reveals an unusual phonon-magnon coupling.

Low-angle polarized neutron scattering has been used to study the coupling between Ni layers and between permalloy layers through silver. It is shown that the coupling between Ni layers is purely bilinear. The coupling between permalloy layers presents bilinear and biquadratic contributions.

Dy/Er superlattices, grown on sapphire, exhibit a succession of magnetic phases. Below the ordering temperature of dysprosium, the helix of dysprosium propagates coherently through paramagnetic erbium. At low temperature, dysprosium becomes ferromagnetically ordered in each layer but the layers are antiferromagnetically stacked. A polarized neutron scattering study of the low-temperature phase is presented. It shows that the antiferromagnetic peaks are never purely spin-flip.