Speaker
Prof.
Kamel Boukheddaden
(Universite de Versailles)
Description
`The direct observation by optical microscopy of the thermally-induced spin transition [1] and the subsequent low-spin high-spin interface propagation inside the thermal hysteresis is a fascinating problem. The kinetic aspects of the spin crossover (SCO) transition investigated under various scan rates was studied so far on powder sample which then average the kinetic effects of the thermal hysteresis. This problem is studied here on the robust spin-crossover single crystal [{Fe(NCSe)(py)$_2$}$_2$(m-bpypz)] for which we followed the dynamics of the thermal hysteresis at several controlled temperature scan rates [2]. In addition to the expected shifts of the switching temperatures, sizable change in the velocity of the high-spin (HS) low-spin (LS) interface dynamics are observed for the first time. Theoretical developments based on a spatiotemporal description of the SCO phenomenon using reaction diffusion equations including the heat balance between the crystal and its immediate environment. We identified the competition between the heat transfer between the crystal and the thermal bath with the temperature scan rate kinetics as key parameter governing the interface velocity, at the origin of the kinetic features of the hysteresis. The experimental data are modelled using a reaction diffusion equation allowing to fairly reproduce the essential features of the spatiotemporal properties of the spin transition.`
References
[1] M. Sy; F. Varret; K. Boukheddaden; G. Bouchez; J. Marrot; S. Kawata S. Kaizaki,« Structure-driven orientation of the high-spin-low-spin interface in a spin-crossover single crystal ». `$\textit{Angew Chem Int Ed Engl}$`, `$\textbf{53}$`, 2014. p. 7539-42.
[2] R. Traiche, M. Sy, H. Oubouchou, G. Bouchez, F. Varret, K. Boukheddaden, `$\textit{J. Phys. Chem. C}$`. (submitted).
[3] M. Paez-Espejo; M. Sy; F. Varret K. Boukheddaden,« Quantitative macroscopic treatment of the spatiotemporal properties of spin crossover solids based on a reaction diffusion equation ». `$\textit{Physical Review B}$`, `$\textbf{89}$`, 2014. p. 024306-024313.
Primary author
Prof.
Kamel Boukheddaden
(Universite de Versailles)
Co-authors
Prof.
Francois Varret
(Universite de Versailles)
Dr
Guillaume Bouchez
(Universite de Versailles)
Dr
Hassane Oubouchou
(Universite de Versailles)
Dr
Mouhamadou Sy
(Universite de Versailles)
Dr
Rachid Traiche
(Universite de Versailles)
