Influence de la composition chimique sur le comportement physique des germaniures ternaires appartenant ay système Ce-Ni-Ge. Détermination des structures magnétiques.

L'étude du système Ce-Ni-Ge a permis d'établir une corrélation étroite entre les propriétés physiques de ces germaniures (gouvernées par l'état fondamental du cérium résultant d'une compétition entre deux types d'interactions : effet Kondo et interaction magnétique de type RKKY) et leur composition chimique. Ainsi, au sein du diagramme de phase ternaire Ce-Ni-Ge, nous avons établi que: (i) les germaniures riches en Ni sont soit des composés de valence intermédiaire (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75), soit des systèmes "fermions lourds" (CeNi2Ge2 et CeNi9Ge4). Notons que pour la séquence CeNi2Ge2 -> Ce3Ni4Ge4 -> CeNiGe, le caractère de valence intermédiaire est de plus en plus marqué; (ii) les germaniures les plus riches en Ge (>50 % atomique) sont antiferromagnétiques à basse température; dans ces composés (Ce2NiGe6, Ce3Ni2Ge7, CeNiGe3, Ce2Ni3Ge5 et CeNiGe2) l'ion cérium est trivalent; les structures magnétiques de ces composés ont été déterminées par diffraction neutronique, la valeur du moment magnétique de Ce3+ (ainsi que la température de Néel) diminue des composés les plus riches en Ge aux composés les moins riches en Ge (propriété associée à la force de l'effet Kondo).The investigation of the Ce-Ni-Ge system have permitted to establish strong correlations between physical properties of these germanides (governed by the Ce-ground state, result of a competition between Kondo and RKKY magnetic interactions) and their chemical composition. In the same phase diagram, we have taken in evidence that : (i) germanides richer in Ni are intermediate valence systems (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75) or "Heavy Fermion" systems (CeNi2Ge2 et CeNi9Ge4). Moreover, in the sequence CeNi2Ge2 -> Ce3Ni4Ge4 -> CeNiGe, the intermediate valence character is more and more present; (ii) germanides richer in Ge (more than 50% Ge-atomic percentage) order antiferromagnetically with Néel temperature TN decreasing with Ge-content in compounds Ce2NiGe6 -> Ce3Ni2Ge7 -> CeNiGe3 -> Ce2Ni3Ge5 -> CeNiGe2. Their magnetic structures have been determined by neutron diffraction and the Ce3+-magnetic moment value obtained at 1.4 K decrease in the same time showing the strength of the Kondo effect

Influence de la composition chimique sur le comportement physique des germaniures ternaires appartenant au système Ce-Ni-Ge. Détermination des structures magnétiques.

L'étude du système Ce-Ni-Ge a permis d'établir une corrélation étroite entre les propriétés physiques de ces germaniures (gouvernées par l'état fondamental du cérium résultant d'une compétition entre deux types d'interactions : effet Kondo et interaction magnétique de type RKKY) et leur composition chimique. Ainsi, au sein du diagramme de phase ternaire Ce-Ni-Ge, nous avons établi que: (i) les germaniures riches en Ni sont soit des composés de valence intermédiaire (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75), soit des systèmes "fermions lourds" (CeNi2Ge2 et CeNi9Ge4). Notons que pour la séquence CeNi2Ge2 → Ce3Ni4Ge4 → CeNiGe, le caractère de valence intermédiaire est de plus en plus marqué; (ii) les germaniures les plus riches en Ge (>50 % atomique) sont antiferromagnétiques à basse température; dans ces composés (Ce2NiGe6, Ce3Ni2Ge7, CeNiGe3, Ce2Ni3Ge5 et CeNiGe2) l'ion cérium est trivalent; les structures magnétiques de ces composés ont été déterminées par diffraction neutronique, la valeur du moment magnétique de Ce3+ (ainsi que la température de Néel) diminue des composés les plus riches en Ge aux composés les moins riches en Ge (propriété associée à la force de l'effet Kondo).The investigation of the Ce-Ni-Ge system have permitted to establish strong correlations between physical properties of these germanides (governed by the Ce-ground state, result of a competition between Kondo and RKKY magnetic interactions) and their chemical composition. In the same phase diagram, we have taken in evidence that : (i) germanides richer in Ni are intermediate valence systems (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75) or "Heavy Fermion" systems (CeNi2Ge2 et CeNi9Ge4). Moreover, in the sequence CeNi2Ge2 → Ce3Ni4Ge4 → CeNiGe, the intermediate valence character is more and more present; (ii) germanides richer in Ge (more than 50% Ge-atomic percentage) order antiferromagnetically with Néel temperature TN decreasing with Ge-content in compounds Ce2NiGe6 → Ce3Ni2Ge7 → CeNiGe3 → Ce2Ni3Ge5 → CeNiGe2. Their magnetic structures have been determined by neutron diffraction and the Ce3+-magnetic moment value obtained at 1.4 K decrease in the same time showing the strength of the Kondo effect

Influence de la composition chimique sur le comportement physique des germaniures ternaires appartenant au système Ce-Ni-Ge. Détermination des structures magnétiques.

The investigation of the Ce-Ni-Ge system have permitted to establish strong correlations between physical properties of these germanides (governed by the Ce-ground state, result of a competition between Kondo and RKKY magnetic interactions) and their chemical composition. In the same phase diagram, we have taken in evidence that : (i) germanides richer in Ni are intermediate valence systems (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75) or "Heavy Fermion" systems (CeNi2Ge2 et CeNi9Ge4). Moreover, in the sequence CeNi2Ge2 → Ce3Ni4Ge4 → CeNiGe, the intermediate valence character is more and more present; (ii) germanides richer in Ge (more than 50% Ge-atomic percentage) order antiferromagnetically with Néel temperature TN decreasing with Ge-content in compounds Ce2NiGe6 → Ce3Ni2Ge7 → CeNiGe3 → Ce2Ni3Ge5 → CeNiGe2. Their magnetic structures have been determined by neutron diffraction and the Ce3+-magnetic moment value obtained at 1.4 K decrease in the same time showing the strength of the Kondo effect.L'étude du système Ce-Ni-Ge a permis d'établir une corrélation étroite entre les propriétés physiques de ces germaniures (gouvernées par l'état fondamental du cérium résultant d'une compétition entre deux types d'interactions : effet Kondo et interaction magnétique de type RKKY) et leur composition chimique. Ainsi, au sein du diagramme de phase ternaire Ce-Ni-Ge, nous avons établi que: (i) les germaniures riches en Ni sont soit des composés de valence intermédiaire (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75), soit des systèmes "fermions lourds" (CeNi2Ge2 et CeNi9Ge4). Notons que pour la séquence CeNi2Ge2 → Ce3Ni4Ge4 → CeNiGe, le caractère de valence intermédiaire est de plus en plus marqué; (ii) les germaniures les plus riches en Ge (>50 % atomique) sont antiferromagnétiques à basse température; dans ces composés (Ce2NiGe6, Ce3Ni2Ge7, CeNiGe3, Ce2Ni3Ge5 et CeNiGe2) l'ion cérium est trivalent; les structures magnétiques de ces composés ont été déterminées par diffraction neutronique, la valeur du moment magnétique de Ce3+ (ainsi que la température de Néel) diminue des composés les plus riches en Ge aux composés les moins riches en Ge (propriété associée à la force de l'effet Kondo)

Influence de la composition chimique sur le comportement physique des germaniures ternaires appartenant au système Ce-Ni-Ge (Détermination des structures magnétiques)

L'étude du diagramme de phase ternaire du système Ce-Ni-Ge a permis de corréler les propriétés physiques de ces germaniures (gouvernées par l'état fondamental du cérium résultant d'une compétition entre deux types d'interactions magnétiques : effet Kondo et interaction RKKY) à leur composition chimique. Nous avons établi que: (i) les germaniures riches en Ni sont soit des composés de valence intermédiaire (CeNiGe, Ce3Ni4Ge4 et CeNi4.25Ge0.75), soit des systèmes "fermions lourds" (CeNi2Ge2 et CeNi9Ge4); (ii) les germaniures les plus riches en Ge sont antiferromagnétiques à basse température; dans ces composés (Ce2NiGe6, Ce3Ni2Ge7, CeNiGe3, Ce2Ni3Ge5 et CeNiGe2) l'ion cérium est trivalent; les structures magnétiques de ces composés ont été déterminées par diffraction neutronique, la valeur du moment magnétique de Ce3+ (ainsi que la température de Néel) diminue des composés les plus riches en Ge aux composés les moins riches en Ge (propriété associée à la force de l'effet Kondo).BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Magnetic ordering in the ternary germanide Ce2Ni3Ge5 as studied by neutron powder diffraction

International audienceNeutronpowderdiffraction investigations on Ce2Ni3Ge5 have been carried out. This compound adopts the U2Co3Si5-type structure (Ibam space group) with only one crystallographic site available for Ce atoms. Magnetisation measurements indicate that Ce2Ni3Ge5 undergoes two antiferromagnetic transitions at low temperature, at TN1=4.8(2) K and TN2=4.2(2) K, respectively. From our neutrondiffraction experiments, only one transition is evidenced, below TN1, Ce2Ni3Ge5 is a collinear antiferromagnet with magnetic moments parallel to the a-axis and equal to 0.4(1) µB/Ce at T = 1.4 K

Magnetic structures of some strongly correlated electron Ce-Ni-Ge systems

Extending our study on the characterisation of the magnetic properties of the ternary germanides based on cerium and nickel, we have performed magnetisation measurements and neutron powder diffraction on CeNiGe3. The antiferromagnetic structure of this compound is dependent on temperature: (i) for T between TN=5.9(2) and 5.0(2) K, the magnetic peaks are associated with the k 1=(1 0 0) propagation vector; (ii) below 5.0(2) K, the two propagation vectors k 1=(1 0 0) and k 2=(0 0.409(1) 1/2) coexist, but the intensities of the magnetic peaks corresponding to k 1 decrease with temperature below 4.1(2) K. We discuss this complex magnetic behaviour in relation to the magnetic structure reported for Ce3Ni2Ge7

The Ce--Ni--Ge system: relationship between chemical composition and magnetic ordering

The investigation on Ce--Ni--Ge phase diagram indicates a relationship between the physical behavior of these ternary germanides and their chemical composition. Those with more than 50 % Ge-atomic percentage order antiferromagnetically, with Néel temperatures TN decreasing with Ge-content. The Ce-magnetic moment at 1.4 K, determined by neutron powder diffraction, also decreases with Ge-content. As for the ternary germanides rich in Ni (\geq 33%), they can be classified as intermediate valence compounds (CeNiGe, Ce3Ni4Ge4 and CeNi4.25Ge0.75) or heavy-fermions systems (CeNi2Ge2 and CeNi9Ge4)

The Ce--Ni--Ge system: relationship between chemical composition and magnetic ordering

The investigation on Ce--Ni--Ge phase diagram indicates a relationship between the physical behavior of these ternary germanides and their chemical composition. Those with more than 50 % Ge-atomic percentage order antiferromagnetically, with Néel temperatures TN decreasing with Ge-content. The Ce-magnetic moment at 1.4 K, determined by neutron powder diffraction, also decreases with Ge-content. As for the ternary germanides rich in Ni (\geq 33%), they can be classified as intermediate valence compounds (CeNiGe, Ce3Ni4Ge4 and CeNi4.25Ge0.75) or heavy-fermions systems (CeNi2Ge2 and CeNi9Ge4)

Incommensurate and commensurate magnetic structures of the ternary germanide CeNiGe3

The structural properties of CeNiGe3 have been investigated via electron diffraction and neutron powder diffraction (NPD). This ternary germanide crystallizes in the orthorhombic SmNiGe3-type structure (Cmmm space group). Electrical resistivity, ac- and dc-magnetization measurements show that CeNiGe3 orders antiferromagnetically below TN = 5.5(2) K and exclude the occurrence at low temperatures of a spin-glass state for CeNiGe3 as previously reported. Specific heat measurements and NPD both reveal two magnetic transitions, observed at TN1 = 5.9(2) K and TN2 = 5.0(2) K. Between TN1 and TN2, the Ce magnetic moments in CeNiGe3 are ordered in a collinear antiferromagnetic structure associated with the k1 = (100) wavevector and showing a relationship with the magnetic structure of the Ce3Ni2Ge7 ternary germanide. Below TN2, this k1 = (100) commensurate magnetic structure coexists with an incommensurate helicoîdal magnetic structure associated with k2 = (00.409(1)1/2). This last magnetic structure is highly preponderant below TN2 (93(5)% in volume). At 1.5 K, the Ce atoms in CeNiGe3 carry a reduced ordered magnetic moment (0.8(2) μB). This value, smaller than that obtained in Ce3Ni2Ge7, results from an important hybridization of the 4f(Ce) orbitals with those of the Ni and Ge ligands

Treatment of myelodysplastic syndromes with excess of blasts by bevacizumab is well tolerated and is associated with a decrease of VEGF plasma level.

International audienceMyelodysplastic syndromes (MDS) are associated with increased bone marrow vascularity and increased levels of various angiogenic factors including Vascular Endothelial Growth Factor (VEGF) which is implicated in the proliferation and survival of leukemic cells. Before the approval of hypomethylating agents in this indication, the GFM conducted a multicenter phase II trial testing the efficacy and tolerance of bevacizumab, a humanized monoclonal antibody against VEGF, in MDS with excess of marrow blasts and its impact on bone marrow angiogenesis. Twenty-one patients were enrolled (16 males and five females) with a median age of 70 years and 19 were evaluable for haematological response after treatment (5 mg/kg IV every 2 weeks for 12 weeks). WHO diagnosis at baseline was RAEB-1 (38%) and RAEB-2 (62%). Treatment was well tolerated and was associated with significant decrease of VEGF plasma level [median (low quartile-high quartile)] from 65.5 pg/ml [LQ (low-quartile)-HQ (high quartile), 35.3-87.3 to 30.4 pg/ml (LQ-HQ, 22.5-34.0 pg/ml)] (p < 0.01) and reduction of bone marrow angiogenesis from a median of 20 vessels/mm(3) (LQ-HQ, 16.5-33 vessels/mm(3)) to 15.5 vessels/mm(3) (LQ-HQ, 10-23.2 vessels/mm(3)) (p = 0.03). On the other hand, only one patient had a significant haematological response with achievement of RBC transfusion independence. Thus, although bevacizumab had a significant impact on VEGF levels and angiogenesis in our patients, very few responses were seen when this drug was used as single agent. Given its good tolerability profile, however, combination of bevacizumab with other drugs, especially hypomethylating agents, could be considered in MDS