Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 27: CE: Poster Session
TT 27.76: Poster
Mittwoch, 24. März 2010, 14:00–18:00, Poster D1
Magnetic anisotropy in the quasi one-dimensional Ising spin-1/2 chain system BaCo2V2O8 — •Sandra Niesen, Gerhard Kolland, Martin Valldor, Oliver Heyer, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln
BaCo2V2O8 contains screw chains of CoO6 octahedra which are running along the c axis of the tetragonal crystal structure and are separated by nonmagnetic Ba2+ und V5+ ions in the aa plane. Due to a compression of the octahedra along c the threefold degeneracy of the t2g orbitals is lifted and the magnetic ground state can be described by an effective Ising spin-1/2 antiferromagnetic chain. Due to a finite inter-chain coupling, BaCo2V2O8 shows long-range antiferromagnetic order below TN≃ 5.5 K with the spins oriented along c.
We have prepared single crystals of BaCo2V2O8 by a spontaneous nucleation method. Here, we present measurements of the magnetization, the specific heat, the thermal expansion, magnetostriction, and the thermal conductivity in magnetic fields up to 17 T. Depending on the field direction, the magnetic field influence is highly anisotropic. In case of H parallel c, the Néel order is strongly suppressed already for low fields, and changes into an incommensurate phase above about 4 T. For fields perpendicular to c, the field influence is much weaker. Besides, this expected Ising anisotropy, we have discovered a new magnetic anisotropy for fields applied within the aa plane. For magnetic fields applied along [110] TN is only weakly suppressed, while for fields applied along [100] TN is completely suppressed for fields above about 10 T. This work is supported by the DFG through SFB 608.