Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 11: CE: Low-dimensional Systems - Materials 2
TT 11.5: Vortrag
Dienstag, 23. März 2010, 10:30–10:45, H18
Unraveling the 1/2 magnetization plateau: a new microscopic magnetic model for CdCu2(BO3)2 — •Oleg Janson1, Alexander Tsirlin1, Johannes Richter2, Yurii Skourski3, and Helge Rosner1 — 1MPI CPfS Dresden — 2University of Magdeburg — 3Dresden High Magnetic Field Laboratory (HLD)
Copper(II) cadmium borate CdCu2(BO3)2 is a spin-1/2 Heisenberg system showing a remarkable 1/2 plateau in the magnetization curve. Based on experimental studies of this compound (χ(T), Cp(T), M(H)), a phenomenological model for its magnetism has been suggested [1]. According to this model, the system can be described as consisting of spin chains and dimers, formed by structurally different atoms Cu1 and Cu2, respectively. However, recent neutron diffraction experiments [2] evidence an inconsistency of this simple chain-dimer model, since both Cu positions show sizable magnetic moments in the ordered state.
We have studied this system using DFT calculations. Typically for Cu2+ materials, the magnetism of CdCu2(BO3)2 can be described by an effective one-orbital approach. Based on the tight-binding fit of the relevant LDA bands, we estimate the antiferromagnetic contribution to the magnetic exchange. The total exchange is obtained by LSDA+U supercell calculations. Exact diagonalization studies of the parameterized Heisenberg model evidence that the new microscopic model consistently describes all existing thermodynamical data. The results of new M(H) measurements and NMR experiments will be briefly discussed.
[1] Hase et al., Phys. Rev. B 72 172412 (2005).
[2] Hase et al., Phys. Rev. B 80 104405 (2009).