NEUTRON DIFFRACTION STUDY OF THE STRUCTURE OF SOME ALUMINIUM- TRANSITION METAL NON PERIODIC CRYSTALS

A neutron scattering investigation of the structure of non periodic crystals Al-X, (X being Mn, Cr or MnCr mixture) has been performed. The negative coherent scattering length of Mn for thermal neutrons provided with a variable contrast with X. Our results are compared both with an X-Ray diffraction pattern and with a similar experiment performed on Al-(Mn,Fe) alloys using thermal neutron scattering. The hypothesis of the isomorphic substitution will be discussed and our results qualitatively checked with various structural models in order to try to determine the location of the atoms in the quasi-lattice

Magnetic structure and magnetic properties of synthetic lindgrenite, Cu-3(OH)(2)(MoO4)(2)

International audienceSynthetic Cu3(OH)2(MoO4)2 consists of Cu3(OH)2 brucite ribbons of edge-sharing copper octahedra connected by MoO4 into a 3D network as in the mineral, lindgrenite, for all temperatures between 1.5 and 300 K. Each ribbon consists of a triangular connection between two different types of copper atom (Cu(1) and 2 Cu(2)) via í3-OH. The MoO4 acts both as one- and three-atom bridges to connect six Cu atoms belonging to three adjacent ribbons. The magnetic properties are consistent with those of ferrimagnetic chains, and the resulting moment of each chain is parallel below the long-range magnetic ordering at 13 K. The Curie constant is 0.468(1) emu K mol-1 of Cu; the Weiss temperature is -14.2(2) K, and the saturation magnetization at 2 K in 50 kOe is 0.41 N íB mol-1 of Cu. Analyses of the neutron powder diffraction reveal an ordered magnetic state where the moment of Cu(1) is antiparallel to those of the two Cu(2); all of them point along the a axis without any sign of geometrical frustration. Any degeneracy that may be present because of the triangular topology of the Cu atoms (s ) 1/2) appears to be lifted by the distortion from an ideal equilateral geometry of the triangle. The entropy, estimated from the heat capacity measurements, attains 50% of the total of 17.7 J K-1 mol-1, close to that expected for three Cu atoms (3R ln 2), up to the long range ordering temperature, and the remaining is associated with the low dimensionality of the material

MAGNETISM OF RANDOMLY CANTED Li-Ti FERRITE

FC-ZFC magnetisation, hysteresis, thermoremanence and neutron diffraction measurements were performed on Li1.125Fe0.625Ti1.25O4. The results are interpreted from domain and wall properties resulting of local canted state where the spin transverse component relaxes between preferential directions