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MA: Magnetismus
MA 12: Kondo / Heavy Fermions
MA 12.4: Vortrag
Montag, 27. März 2006, 17:15–17:30, HSZ 403
Thermodynamic properties of the magnetic layered compound BaNi2V2O8 — •William Knafo1,2, Stephanie Drobnik1,2, Kai Grube1, Hilbert von Löhneysen1,2, Christoph Meingast1, Paul Popovich1, Peter Schweiss1, and Thomas Wolf1 — 1Forschungszentrum Karlsruhe, Institut für Festkörperphysik, D-76021 Karlsruhe, Germany. — 2Physikalisches Institut, Universität Karlsruhe, D-76128 Karlsruhe, Germany.
BaNi2V2O8 is a quasi two-dimensional magnetic system which consists of a planar honeycomb arrangement of spin-1 ions of Ni2+. Although a small inter-plane interaction leads to three-dimensional magnetic order below TN = 47 K, this system has been recently proposed as a candidate for a two-dimensional XY magnetic model where a Kosterlitz-Thouless transition should occur [1]. To test this scenario, we have grown large single crystals of BaNi2V2O8 and have investigated their thermodynamic properties. We present here specific heat, thermal expansion, magnetostriction, and magnetization measurements, which were carried out for temperatures T between 3 and 300 K and magnetic fields H up to 14 T. The main features of the resulting (H,T) phase diagram are (i) an increase of TN when the field is applied in the plane and (ii) a cross-over to a "spin-flop" phase below TN for fields higher than HSF≈ 1.4 T. The anisotropy of the magnetic moments and the dimensionality of their interactions will be considered carefully to discuss if a two dimensional XY model is relevant or not for this system.
[1] N. Rogado et al., Phys. Rev. B 65, 144443 (2002).