Interplay between elastic interactions in a core-shell model for spin-crossover nanoparticles

Spin Crossover Nanomaterials: From Fundamental Concepts to Devices

“…In addition, even if the concepts of thermodynamics can be still used at small sizes, strictly speaking the notions of “phase equilibrium” and “phase transition” vanish and for further size reduction the thermodynamic description completely fails . Some of these issues have been addressed more deeply for SCO systems using different microscopic models, including the role of particle shape, surface relaxations, and the particle environment . For the dominant role of this latter in the following we discuss matrix/interface effects in more details.…”

“…As a matter of fact, the mechano‐elastic model of Enachescu (vide supra) can be considered as a first variant of the different models, which were developed with the common idea of analyzing the lattice misfit and the resulting changes of elastic energy in order to account for the phase stability and different physical properties of the core and the shell. Boukheddaden and co‐workers used extensive Monte Carlo simulations in combination with the well‐known Ising‐like model and later on using more sophisticated electro‐elastic (spin‐phonon) models as well . This powerful approach allowed them to analyze the different manifestations of the coupling between the core and the shell (shift of the transition temperature, change of the hysteresis width, emergence of residual fractions, acceleration of the kinetics), the role of the particle geometry (core and shell thickness, shape, etc.…”

“…Overall, the most encouraging (and somewhat unexpected) experimental result obtained with these different nanoscale SCO materials is that the hysteresis and a virtually complete spin transition can be preserved even in very small objects (<5 nm) . On the other hand, experiment revealed a range of different behaviors (vide infra), which have not yet been fully rationalized, despite the development of several thermodynamical, continuum mechanics, and statistical physics approaches to this aim. This problem will be addressed in the second part of this review, while the third part will be devoted to examples of successful integration of SCO nanomaterials into devices.…”

Molecular Spin Crossover Materials: Review of the Lattice Dynamical Properties

“…This coupling introduces the characteristic HS–HS, LS–LS, and HS–LS equilibrium distances, which allow to reproduce various experimental observations on cooperative SCO systems. Indeed, different variants of these “ball and spring” models have been developed to investigate clustering phenomena, structural dynamics following short laser impacts, and size reduction effects . As an example, Figure shows the spatial mapping of the local spin state and the local strain during the HS to LS spin transition in a cooperative system.…”

Role of open boundary conditions on the hysteretic behaviour of one-dimensional spin crossover nanoparticles

“…1,[13][14][15] In addition to the progress made from the experimental side, the theoretical one has also matured, and several models as Ising, 16,17 atom-phonon coupling, 18,19 different issues and to provide new insights into the switching mechanism involved in these systems. Strong cooperative properties as multi-step 24,25 or incomplete transition [26][27][28] have been explained, but some features regarding the size effect cannot be treated exactly as a consequence of the fact that models have been solved only for periodic conditions. So, as a consequence most of the elastic models take into account the volume change at the transition, they can be solved only numerically, using Monte Carlo or Molecular Dynamics 29,30 simulations.…”