| SM ISO690:2012|
KLOKISHNER, Sophia; PALII, Andrew; OSTROVSKY, Sergei M.; REU, Oleg; TSUKERBLAT, Boris; LIU, Shixia; DECURTINS, Silvio. Cooperative spin crossover in mono- and binuclear cluster compounds. In: Materials Science and Condensed Matter Physics. Editia a 8-a, 12-16 septembrie 2016, Chişinău. Chişinău: Institutul de Fizică Aplicată, 2016, p. 48. ISBN 978-9975-9787-1-2.
|Materials Science and Condensed Matter Physics
Editia a 8-a, 2016
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
8-th Edition, Chişinău, Moldova, 12-16 septembrie 2016
A new microscopic approach to the problem of cooperative spin crossover in crystals containing mono- or binuclear clusters as structural units is suggested. As for a single impurity center  the coupling of each spin crossover ion to both molecular vibrations and phonons is taken into account and shown to give rise to a cooperative interaction bilinear on molecular and crystalline normal coordinates. Besides this intercluster interaction responsible for the spin transformation the crystal Hamiltonian also contains the coupling of the electrons of each spin crossover center to local vibrations. In addition, for binuclear cluster compounds the model allows for different strength Coulomb interaction  in the pairs of ions in the ls-ls, hs-ls and hs-hs (ls‒low-spin, hs‒high-spin) states. Within the framework of the suggested approach all types of the observed spin transitions in mononuclear cluster compounds can be described and, namely, the gradual and abrupt transitions as well as the transition with a single hysteresis loop. As to crystals containing as a structural element binuclear clusters the model reproduces (i) the one step ls-ls to hs-hs transition in which both ions pass from the ls state to the hs state; (ii) the two- step transitions with a plateau and two-step transitions with a hysteresis loop on one or both steps; (iii) partial transitions in which only one ion changes its spin state, while another remains in the hs-state in the whole temperature range. Within the framework of the developed approach the experimental data on spin transitions in the mononuclear [Fe(ptz)6](BF4)2, binuclear [Fe(bpym)(NCSe)2]2bpym and [Fe(bt)(NCS)2]2bpym cluster compounds have been reproduced (Fig.1).