Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena
TT 6.23: Poster
Montag, 23. März 2009, 13:00–16:45, P1A
Specific heat of the highly anisotropic antiferromagnet [Cu(pyz)2(HF2)]PF6 — •R. Beyer1, M. Uhlarz1, J. Wosnitza1, and J.A. Schlueter2 — 1Hochfeld-Magnetlabor (HLD), Forschungszentrum Dresden-Rossendorf (FZD), Dresden, Germany — 2Materials Science Division, Argonne National Laboratory, Argonne, USA
The metal-organic compound [Cu(pyz)2(HF2)]X with X = PF6 exhibits a quasi-cubic lattice of copper ions (S = 1/2), but the magnetic properties show a predominantly two-dimensional (2D) nature due to a large anisotropy in the exchange couplings. The magnetic entropy and the antiferromagnetic ordering, eventually occurring at about 4.4 K, were investigated by specific-heat measurements. For this we established a continuous relaxation-time technique, using a single relaxation process to get specific heat data over a wide temperature range. The calorimetric investigations, performed between 2 and 100 K and in magnetic fields up to 14 T, have revealed a non-monotonic field dependence of the ordering temperature. The results are as expected from the model for a S = 1/2 2D square-lattice quantum Heisenberg antiferromagnet with an additional weak interlayer exchange (via Cu-F-H-F-Cu bonds).
In comparison to the X = BF4 compound, the antiferromagnetically ordered phase extends to much higher temperatures. In a more detailed analysis, we can extract all exchange interactions with an interlayer coupling ten times larger than in X = BF4. Thus, the 2D character is significantly reduced in X = PF6.