Berlin 2015 – wissenschaftliches Programm
TT 71.21: Poster
Mittwoch, 18. März 2015, 15:00–18:00, Poster B
Thermodynamics of the Ising chain compound CoNb2O6 in transverse magnetic field — •Daniel Brüning1, Simon Scharffe1, Victoria Cho1, Martin Valldor1,2, and Thomas Lorenz1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany
CoNb2O6 is a model system to investigate a quantum phase transition in magnetic fields. The structure consists of layers of CoO6 octhahedrons separated by non-magnetic NbO6 layers. The edge-sharing oxygen octahedrons link the Co2+spins through Co-O-Co superexchange and form 1D ferromagnetic zigzag chains along the orthorhombic c axis. Crystal field effects lead to an easy-axis anisotropy of the Co2+ moments in the ac plane and to an effective spin-1/2 chain system described by the Ising model. A purely 1D Ising chain develops long-range order at zero temperature only and a transverse field induces a quantum phase transition into a quantum disordered state. Due to small inter-chain couplings J|| ≈ 0.01 · J⊥, CoNb2O6 shows 3D long-range antiferromagnetic order below TN=2.95 K. Because a magnetic field parallel to the b axis is normal to the easy-axis of the spin chain it is possible to study the complex interplay of 3D ordering and 1D quantum phase transitions. We present specific heat and magnetization measurements from about 0.3 to 10 K and discuss the phase diagram. The theoretical model of the Ising chain in transverse magnetic field is completely solvable and we compare our measurements to the corresponding calculations.