Dresden 2003 – wissenschaftliches Programm
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MA: Magnetismus
MA 14: Poster: Schichten(1-31), Spinabh.Trsp.(32-47), Exch.Bias(48-54), Spindyn.(55-64), Mikromag.(65-76), Partikel(77-88), Oflmag.(89-92), Spinelektr.(93-98), Elektr.Theo.(99-103), Mikromag+PhasÜ+Aniso.(104-122), MagnMat.(123-134), Messm+Mol-Mag.(135-139), Kondo(140-151)
MA 14.147: Poster
Dienstag, 25. März 2003, 15:15–19:15, Zelt
Investigation of the Spin-Peierls-like Phase Transition in [1-benzyl-4-aminopyridinium][bis(maleonitriledithiolato)nickelate(III)] — •X. M. Ren1, R. K. Kremer1, O. Oeckler1, and Q. J. Meng2 — 1MPI für Festkörperforschung, Stuttgart, Germany — 2Coordination Chemistry Institute, Nanjing University, Nanjing, China
The novel compound, [1-benzyl-4-aminopyridinium][bis(maleonitriledithiolato)nickelate(III)], contains linear Ni(III) (3d7, S=1/2) tetramer units. It shows an unusual magnetic transition to a nonmagnetic ground state associated with a structural phase transition at TC=189 K. The single crystal structure determination indicates that the almost equidistant tetramer unit present in the high-temperature phase undergoes a distance alternation leading to two short bonded dimers in low-temperature phase. In order to understand the nature of this phase transition we have determined the temperature dependence of the magnetic susceptibility at ambient conditions and under hydrostatic pressure up to 1 GPa. Hydrostatic pressure raises TC non-linearly up to ≈ 300K at 1 GPa indicating sizeable magnetoelastic coupling. The temperature dependence of the zero- pressure magnetic susceptibility above TC can successfully be modeled using a Heisenberg Hamiltonian for a linear S=1/2 tetramer with two individual exchange constants. Our results evidence afm coupling between terminal and central Ni moments while the two central moments couple ferromagnetically. We suggest that the structural phase transition significantly enhances the afm coupling and thus drives the system towards a nonmagnetic singlet ground state.