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F. Eder:
"Thermal Expansion and Magnetostriction of FeII Spin Crossover Compounds";
Betreuer/in(nen): W. Linert, R. Grössinger; Institut für Angewandte Syntehsechemie, 2010; Abschlussprüfung: 10.06.2010.

In some transition metal complexes a change of the electronic state from a "low spin" state
(LS) to a "high spin" state (HS) can be induced e.g. by changing the temperature or the
magnetic field. In general this phenomenon is accompanied by a hysteresis. The Spin
Crossover complex [Fe(ptz)6(BF4)2] exhibits a very abrupt spin transition at 130K and the
hysteresis cycle is about 10K. [Fe(4ditz)3(BF4)2] however has a more gradual transition at 90K
and a very small hysteresis. The experimental results gained from detailed thermal
expansion investigations and magnetostriction measurements as well as their interpretation
are presented for both complexes. Moreover the effect of a static magnetic field on the spin
transition, namely a downward shift of the transition temperature is treated. Furthermore
two theoretical approaches, a thermodynamic approach within the framework of the Gibbs
free energy functional as well as an Ising like model including molecular vibrations are
outlined. Numerical simulations investigating the influence of the cooperativity and an
external magnetic field on a spin transition are presented.