Evolution of self-organized spin domains under light in single-crystalline[Fe(ptz)6](BF4)2

Abstract

We study domain growth upon the light-induced phase separation (LIPS) in the spin-crossover $[\text{Fe}{(\text{ptz})}_{6}]{({\text{BF}}_{4})}_{2}$ single crystal under clarified conditions of intensity of light and temperature. Our primary motivation is to model the relaxation behavior of a spin-crossover system under light in the spinodal regime. At this end, we built a discrete spatiotemporal hierarchy of coupled equations, which can be regarded as an efficient scheme for simulating the phase separation under light as well as for obtaining the equilibrium mean-field solutions of lattice models having complex structures. We found that in the spinodal regime under light, initial homogeneous states self-organize into spin domains after some incubation time. The evolution patterns of the high- and low-spin domains revealed that the self-organization proceeds roughly in two regimes, viz. diffusion of interfaces in the early stage followed by a growth regime. The analysis of the correlation function shows that the characteristic domain size behaves as $R(t)\ensuremath{\sim}{t}^{1/2}$, following the Allen-Cahn law.