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DPG

Berlin 2005 – scientific programme

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MA: Magnetismus

MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65

MA 20.160: Poster

Monday, March 7, 2005, 14:00–18:00, Poster TU C

Neutron Diffraction Studies of the Long-Range Magnetic Ordering in the Antiferromagnetic Quantum Chain System CuBr2 — •Reinhard K Kremer1, Michael Banks1, Arndt Simon1, and Bachir Ouladdiaf21MPI-FKF, 70569 Stuttgart — 2ILL Grenoble, CEDEX 9

Historically, the binary CuBr2 and the structurally similar CuCl2 are among the very first systems the magnetic properties of which were analyzed in terms of a linear spin chain arrangements. Low-dimensional magnetism with typical signatures , e.g. a broad short-range ordering maxima in the susceptibility have been found. The antiferromagnetic (afm) intra-chain exchange parameters are significant (e.g. ≈320K for CuBr2), however, both systems are far from representing ideal one-dimensional magnets as must be concluded from the rather high transition temperatures to long-range ordering (e.g. 74 K for CuBr2) indicating appreciable inter-chain coupling. To the best of our knowledge, the magnetic structures of CuBr2 and CuCl2 remained unsolved until now. We studied the afm ordering of CuBr2 in detail by neutron powder diffraction using ILL’s high flux powder diffractometer D20 in its high resolution option. Below TN, two very weak additional reflections of magnetic origin were identified which can be indexed with a propagation vector (0,0.54,0) indicating an incommensurate antiferromagnetic structure. A first analysis assumes a longitudinal amplitude modulation with moments (µ = 0.2 µB ) oriented along (0,1,0). In the critical regime characteristic magnetoelastic anomalies are observed for the b lattice parameter and the monoclinic angle β.

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