https://doi.org/10.1007/s100510051035
Cooperativity in a spin transition ferrous polymer: Interacting domain model, thermodynamic, optical and EPR study
Centre de Physique Moléculaire Optique et Hertzienne (UMR
Université Bordeaux I-CNRS 5798) ,
351 Cours de la Libération, 33405 Talence Cedex, France
Received:
27
November
1998
Revised:
19
April
1999
Published online: 13 August 2012
A new thermodynamic model is proposed in order to account for the high
spin 
low spin conversion in metal-organic polymers. The model, based
on the idea that the spin conversion occurs in interacting domains of
like-spin metal ions, allows to explain most of the important features
of various types of spin conversion. The sine qua non condition
of the existence of spin transitions with hysteresis is obtained. In the
case of very large cooperativity, the model predicts unusual behaviour
of the spin conversion system due to a low-temperature metastable high
spin state. Existence of such a state is interesting in the context of the
light induced excited spin state trapping recently observed in some ferrous
compounds. The model is applied to interpret the spin transition in
polycrystalline ferrous polymer
![$[\mathrm{Fe}_{1-y}\mathrm{Cu}_{y} (\mathrm{Htrz})_{2}\mathrm{trz}] (\mathrm{BF}_{4})$](/articles/epjb/abs/1999/24/b8783/b8783_tex_eq2.png)
with y = 0.00, 0.01 and 0.10, detected by differential scanning calorimetry,
optical reflectivity and electron paramagnetic resonance. The domain size
and the interaction energy between the domains are estimated as, respectively,
n = 11 and 
for the y = 0 compound.
As the copper content is growing, n and Γ tend to decrease, resulting
in transformations of the shape of hysteresis loop which becomes less steep,
narrows and shifts to lower temperatures. The electron paramagnetic resonance
gives further evidence of the presence of like-spin domains.
PACS: 65.50.+m – Thermodynamic properties and entropy / 78.40.Me – Organic compounds and polymers / 76.30.Fc – Iron group (3d) ions and impurities (Ti-Cu)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999
