Berlin 2005 – wissenschaftliches Programm

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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

Montag, 7. März 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 Ouladdiaf² — ¹MPI-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 T_N, 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 µ_B ) oriented along (0,1,0). In the critical regime characteristic magnetoelastic anomalies are observed for the b lattice parameter and the monoclinic angle β.