Abstract
Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz) 2 {Pt(CN) 4 }]·3H 2 O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, high-spin low-spin (HS-LS) state, below 153 K, where only one of the two crystallographic Fe(II) centers switches from the HS to HS-LS state. In comparison with crystals undergoing a complete spin transition, the present transformation involves smaller volume changes at the transition, which helps to preserving the crystal’s integrity. By analyzing the spatio-temporal properties of this spin transition, we evidenced a direct correlation between the orientation and shape of HS/HS-LS domain wall with the crystal’s shape. Thanks to the small volume change accompanying this spin transition, the analysis of the experimental data by an anisotropic reaction-diffusion model becomes very relevant and leads to an excellent agreement with the experimental observations.
Highlights
Because of the growing societal requirement of information processing and big data storage, the design of devices with reversible and high density storage capacities as well as fast responses becomes mandatory
The present work contains experimental investigations of optical microscopy performed at several temperatures in the thermal hysteresis region in order to observe the spatio-temporal features of the first-order spin transition of the title compound
To understand the physical mechanism of the interface propagation in this particular system, in which the spin transition is accompanied with a small volume change, we developed an appropriate modeling, based on a reaction diffusion description, allowing to reproduce the experimental spatiotemporal features of the current first-order spin crossover (SCO) transition
Summary
Because of the growing societal requirement of information processing and big data storage, the design of devices with reversible and high density storage capacities as well as fast responses becomes mandatory. OM allows the study of the first-order phase transitions of SCO solids on a unique single crystal, which constitutes an undeniable progress towards a deep understanding of the fundamental aspects of this phenomenon This technique provides valuable information on the electronic properties of the studied single crystals along the transition and on the modification of their elastic properties, when the spin transition is accompanied with a significant volume change. OM studies, performed on the resilient SCO single crystal [Fe(NCSe)(py) (μ-bpypz)] (py = pyridine and bpypz = 3,5-bis(2-pyridyl)-pyrazolate) [37,42,43,44], allowed for the first-time to monitor the motion of the HS-LS interface on both cooling and heating processes, whose corresponding velocities were estimated in the range 4–6 μm·s−1 In the latter case, due to the regular shape of the crystals, made of rectangular platelets along the direction of the interface propagation, the shape of the HS-LS interface remained unchanged during its motion.
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