Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 47: Correlated Electrons: Spin Systems and Itinerant Magnets 2
TT 47.6: Vortrag
Freitag, 30. März 2012, 10:45–11:00, H 0104
Thermal Transport in the Spin-Ice compound Dy2Ti2O7 — •Gerhard Kolland, Oliver Breunig, Simon Scharffe, Johanna Frielingsdorf, Martin Valldor, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln, Germany
The magnetic Dy sites in Dy2Ti2O7 form a pyrochlore lattice consisting of corner-sharing tetrahedra. A strong crystal field results in an Ising anisotropy of the magnetic moments of the Dy sites, which align along their local easy axis in the [111]-direction, pointing into or out of the tetrahedra. As a consequence, the spin system is geometrically frustrated. Possible ground-states at temperatures below 1 K are given by the “ice-rule”: two spins point into and two out of a tetrahedron. This behaviour is analogous to the hydrogen displacement in water ice, revealing a residual entropy for T→0. Excited states can be created by flipping one spin – leading to the configurations of “1-in/3-out” and “3-in/1-out”. In zero magnetic field, these excitations can easily propagate and are discussed as magnetic monopoles [1]. We measured the thermal conductivity down to 300 mK for external magnetic fields up to 8 T. The thermal conductivity is strongly field dependent and anisotropic with respect to the field direction. To investigate the influence of the magnetic excitations on the heat transport we compare our data to the thermal conductivity of Dy2−xYxTi2O7 with x=1,2.
Work supported by the DFG through SFB 608.
Castelnovo et. al. (2008). Nature, 451(7174), 42-5