Three-dimensional electroelastic modeling of the nucleation and propagation of the spin domains in spin-crossover materials

Abstract

A three dimensional version of the electro-elastic model allowing the description of spin-crossover (SCO) materials taking into account for the volume change at the transition between the LS and the HS spin states is developed. The investigations are realized on a rectangular parallelepiped lattice with a cubic symmetry. The SCO units are modeled by two-states fictitious spins coupled by springs whose equilibrium distances depend on the spin states. We implemented massive parallel simulations using CUDA (Compute Unified Device Architecture) programming where the spin states are updated using Monte Carlo Metropolis algorithm while the mechanical relaxation (lattice position) is performed by molecular dynamics. In this work, we investigated: (i) the case of the thermal spin transition showing the macroscopic deformation of the parallelepiped accompanying the propagation of single domains, and (ii) the isothermal relaxation of the photoinduced metastable HS fraction at low temperature. In both cases, the interplay between the electronic and the structural aspects of these transformations is analyzed and discussed in relation with the model parameters.

Variation of the Cooperativity in Diluted Hofmann-Based Spin-Crossover Coordination Solids {Fe1–xMx(pz)[Pd(CN)4]}

“…For reproducing the experimental data, we use a 3D mechanoelastic model in which the individual molecules are symbolized as spheres in the vertices of a fcc (face-centered cubic) open boundary lattice. − Each molecule (excepting those situated on the outermost layers and those located on edge) is connected to its closest six molecules situated in the same layer by springs with an elastic constant k 1 and with other six molecules (three in the layer below and three in the layer above) by springs with an elastic constant k 2 . These elastic constants stand for the cooperativity of the systemthe triangular configuration has been chosen not only for better system stability but also to allow one single elastic constant for springs connecting SCO molecules.…”

“…Importantly, in SCO solids, the superposition of short- and long-range interactions propagates throughout the lattices due to significant changes in the molecular volume, consequently leading to the macroscopic communication between SCO centers, known as cooperative effects . − Understanding the origin and exploring the mechanistic details of cooperativity in SCO solids have always been considered a central research theme, owing to its tremendous impact on designing memory, sensor, and switching devices . In the literature, it is understood in terms of various models, including the phenomenological thermodynamic model (such as the mean-field model) and the lattice expansion model, ,,− and more recently the mechanoelastic model was developed to highlight the detailed microscopic scenario using a nucleation and growth mechanism. − In the mechanoelastic model, the SCO centers are considered rigid spheres in an open boundary lattice. They are connected via springs that can be compressed and elongated during spin-state switching (as the volume change produces an immediate change in the elastic forces to the neighboring springs).…”

The effect of inert dopant ions on spin-crossover materials is not simply controlled by chemical pressure

“…The materials’ SCO profiles were simulated using a 3D mechanoelastic approach. 69–71 The sample used is a lattice of 6400 molecules, represented as balls situated at the sites of a face-centered cubic structure of five interconnected layers with open boundary conditions (Fig. 3).…”

Electro-Elastic Modeling of Thermal Spin Transition in Diluted Spin-Crossover Single Crystals

“…The control of the width of the plateau region through metal dilution is of high importance, and the extension of the present model for polynuclear SCO materials, accounting for antagonist elastic effects [33], is also a very promising objective. Finally, the recent progresses in the treatment of 3D versions [88,89] of elastic models opens new opportunities for interesting investigations of the dilution effects in more realistic lattices.…”