Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 45: Correlated Electrons: Poster Session
TT 45.65: Poster
Donnerstag, 29. März 2012, 15:00–19:00, Poster B
Phase diagram of the Ising chain compound Nb2O6 in transverse magnetic field — •Simon Scharffe, Oliver Breunig, Johanna Frielingsdorf, Martin Valldor, Michael Seher, and Thomas Lorenz — II. Physikalisches Insitut, Universität zu Köln
CoNb2O6 is a model system to investigate a quantum phase transition in magnetic fields. The structure consists of layers of CoO6 octahedrons separated by non-magnetic NbO6 layers. Within each layer the Co2+spins are linked through superexchange and form 1D ferromagnetic zigzag chains along the c axis. Due to crystal field effects (compression of the CoO6 octahedrons) an easy-axis anisotropy of the Co2+moments is present, which leads to an effective spin-1/2 system described by the Ising model. The easy axis is in the a c plane, and alternates by ± 31∘ with respect to the c axis for neighboring chains.
Due to small inter-chain couplings J|| ≈ 0.01 · J⊥ the system shows long-range antiferromagnetic order, which is insommensurate below TN1=2.9K and becomes commensurate at TN2=1.9K.
A magnetic field parallel to the b axis is normal to the easy axis and allows to study the quantum phase transition of an Ising-spin chain in tranverse field. The system is driven to its quantum critical point between a quasi 1D ferromagnet to a quantum paramagnet.
Only few studies of the transverse field case are available so far. We present measurements of specific heat and magnetization in a temperature range from about 0.3 to up to 10 K and discuss the phase diagram.
This work was supported by the DFG through SFB 608.