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TT: Fachverband Tiefe Temperaturen

TT 40: Poster Session Correlated Electrons

TT 40.55: Poster

Mittwoch, 13. März 2013, 15:00–19:00, Poster D

Phase diagram of the effective Ising spin-1/2 chain compound CoNb₂O₆ in transverse magnetic field — •Simon Scharffe, Oliver Breunig, Johanna Frielingsdorf, Martin Valldor, Markus Garst, Eran Sela, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln

CoNb₂O₆ is a model system to investigate the quantum phase transition of Ising spins in a transverse magnetic field. The interesting physics exclusively takes place within the magnetic CoO₆ layers, separated by non-magnetic NbO₆ layers. The edge-sharing oxygen octahedrons link the Co²⁺spins and form 1D ferromagnetic chains along the c axis. Due to crystal field effects an easy-axis anisotropy is present, which leads to an effective spin-1/2 system described by the Ising model. Small inter-chain couplings J_|| ≈ 0.01 · J_⊥ cause long-range antiferromagnetic order, which is incommensurate below T_N1=2.95 K and becomes commensurate at T_N2=1.97 K. A magnetic field parallel to the b axis is normal to the easy axis and allows to study the quantum phase transition in transverse field. Above 5 T the system is driven through its quantum critical point to a quantum paramagnet. Only few studies of the transverse field case are available. We present measurements of specific heat and magnetization in a temperature range from about 0.3 up to 10 K and discuss the phase diagram. We compare our measurements with the theoretical predictions of the 1D Ising model in a transverse field.

This work was supported by the DFG through SFB 608.