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Journal Articles Physical Review B Year : 2012

Structural aspects of the relaxation process in spin crossover solids

Abstract

We present a non-equilibrium study of the relaxation process in spin crossover solids using numerical simulations of a recently introduced two variable elastic Ising-like model. We analyse the structural lattice distortions accompanying the relaxation from the metastable high spin to the ground low spin state as a function of cooperativity. In the highly cooperative case, a sigmoidal relaxation behaviour of the high spin fraction nHS is described, and occurs jointly with a structural phase separation process. The mean lattice spacing follows a similar sigmoidal trend, owing to the interplay between electronic and lattice variables in the Hamiltonian. Weakly cooperative systems are characterized by single exponential relaxations of the high spin fraction, the corresponding structural transformation proceeds homogeneously with a progressive relaxation of the mean lattice spacing. Long relaxation tail effects are also observed. We highlight the development of lattice strain accompanying the spin transition, and show that structural phase rebuilding proceeds in the late stage of the relaxation by releasing residual strain. Under specific conditions, a temporal decoupling between the electronic and lattice variables is observed, which may have direct applications for interpreting time resolved spectroscopic or diffraction experiments, and for elucidating unusual structural behaviours, such as the development of superstructures, modulated structures or transient phases.
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Dates and versions

hal-03538333 , version 1 (21-01-2022)

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W. Nicolazzi, S. Pillet. Structural aspects of the relaxation process in spin crossover solids: phase separation, mapping of lattice strain, and domain wall structure. Physical Review B, 2012, 85 (9), pp.094101. ⟨10.1103/PhysRevB.85.094101⟩. ⟨hal-03538333⟩
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