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TT: Fachverband Tiefe Temperaturen

TT 16: Correlated Electrons: Low-dimensional Systems - Materials 1

TT 16.4: Vortrag

Dienstag, 24. März 2009, 10:15–10:30, HSZ 304

Crystal water induced switching of magnetic active orbitals in CuCl₂ — •Miriam Schmitt¹, Oleg Janson¹, Marcus Schmidt¹, Stefan Hoffmann¹, Walter Schnelle¹, Stefan-Ludwig Drechsler², and Helge Rosner¹ — ¹MPI CPfS, Dresden, Germany — ²IFW Dresden, Germany

Low dimensional transition metal compounds show an intimate interplay between the crystal structure and their magnetism. Nevertheless, it is a widespread belief that crystal water has just a moderate, renormalizing influence on the magnetic properties due to a modification of interactomic distances. In contrast, the dehydration of CuCl₂·2H₂O to CuCl₂ leads to a dramatic change in magnetic behavior and ground state – driving a classical example of a 3D antiferromagnet (T_N=4.3 K) to a quasi 1D system with long range order below T∼23 K. Combining electronic structure calculations based on DFT, model calculations and thermodynamical measurements we reveal the microscopic origin of this surprising behavior. Regarding our calculations CuCl₂ can be well described as a frustrated J₁–J₂ Heisenberg chain with ferromagnetic exchange J₁ and J₂/J₁ ∼ -1.5 predicting a helical ground state. The hydration of CuCl₂ flips the magnetically active orbitals, resulting in a fundamental change of the coupling regime. As CuCl₂ consists edge-shared Cu-Cl₄ plaquettes with the magnetically active orbital in the chain plane, CuCl₂·2H₂O forms its magnetically active orbitals out of the former chain plane resulting in isolated plaquettes arranged back to back. This new arrangement strongly reduces the former in-chain interactions yielding an almost isotropic 3D coupling.