Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 35: CE: Low-dimensional Systems - Materials 3
TT 35.6: Vortrag
Mittwoch, 16. März 2011, 15:30–15:45, HSZ 301
Magnetic phase diagram of quasi one-dimensional Ising spin-1/2 chain system BaCo2V2O8 — •Sandra Niesen, Gerhard Kolland, Oliver Heyer, Daniel Löwen, Martin Valldor, 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. 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.
Here, we present the magnetic phase diagram extracted from measurements of the magnetization, the specific heat, the thermal expansion, magnetostriction, and the thermal conductivity in magnetic fields up to 17 T. The magnetic field influence is highly anisotropic: in case of H || c, the Néel order is strongly suppressed already for low fields and changes into an incommensurate phase above about 4 T. Apart from this expected Ising anisotropy, we have discovered a new magnetic anisotropy for fields applied within the aa plane.
For fields applied along [110] TN is only weakly suppressed, while for magnetic fields applied along [100] TN is completely suppressed above about 10 T. In this case the T-H-phase boundary exhibits most probably a quantum critical point.
This work is supported by the DFG through SFB 608.