Dresden 2014 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 55: Poster II
MA 55.70: Poster
Freitag, 4. April 2014, 10:30–13:30, P2
Spin-liquid phase and order-by-disorder on the frustrated swedenborgite-lattice — •Stefan Buhrandt1 and Lars Fritz2 — 1Institut für theoretische Physik, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany — 2Institute for Theoretical Physics, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands
Geometrical frustration is the phenomenon that not all anti-ferromagnetic exchange interactions in a system can be completely satisfied simultaneously due to the geometry of the underlying lattice. A lattice exhibiting a very unusual and interesting exchange topology is formed by the magnetic ions in compounds of the swedenborgite family, where the magnetic ions reside on alternating stacked triangular and Kagomé layers. While in general there are four distinct next neighbor exchange interactions allowed by symmetry on this lattice, a simplified model with only two distinct interactions, J1, describing the exchange inside the Kagomé layers and J2, accounting for the exchange between the Kagomé and triangular layers, is widely used and has proven to be sufficient to reproduce experimental findings. Depending on the ratio J2/J1, the ground state of the model is either unique or highly degenerated. In the latter case, coplanar ground states are eventually selected by an entropic order-by-disorder transition at low temperatures. The presence of soft modes in these ground states reduces the specific heat per spin in the limit T → 0 from 1 to 15/16. Additionally, we find a broad spin-liquid regime over a wide range of parameters and temperatures, which might persist even in the presence of small additional interactions.