Hexagonal-Shaped Spin Crossover Nanoparticles Studied by Ising-Like Model Solved by Local Mean Field Approximation

Catherine Cazelles,Mamadou Ndiaye,Pierre-Richard Dahoo,Jorge Linares,Kamel Boukheddaden

doi:10.3390/magnetochemistry7050069

Abstract

The properties of spin crossover (SCO) nanoparticles were studied for five 2D hexagonal lattice structures of increasing sizes embedded in a matrix, thus affecting the thermal properties of the SCO region. These effects were modeled using the Ising-like model in the framework of local mean field approximation (LMFA). The systematic combined effect of the different types of couplings, consisting of (i) bulk short- and long-range interactions and (ii) edge and corner interactions at the surface mediated by the matrix environment, were investigated by using parameter values typical of SCO complexes. Gradual two and three hysteretic transition curves from the LS to HS states were obtained. The results were interpreted in terms of the competition between the structure-dependent order and disorder temperatures (TO.D.) of internal coupling origin and the ligand field-dependent equilibrium temperatures (Teq) of external origin.

Highlights

Over the last few decades, the storage capacity and downsizing of electronic components have been of concern for potential industrial applications in accordance with Moore’s law
In [48], we showed that the size dependence of the equilibrium temperature Teq of such a system could be described analytically, and, more precisely, we reached the conclusion that the equilibrium temperature was the result of a null total effective ligand-field
The value of the L/kB parameter was gradually increased from 0 to 160 K, and calculations were made for the H6 (91 atoms) system It is worth mentioning that modifying the values of L/kB correspond to a change in the interaction strength between the nanoparticle and its environment which is achieved with a change in the chemical nature of the matrix

Summary

Introduction

Over the last few decades, the storage capacity and downsizing of electronic components have been of concern for potential industrial applications in accordance with Moore’s law. Molecular electronics, based on the taming and manipulation of electrical, optical, or magnetic signals in devices composed of molecules, is continuously being developed at an ever-increasing rate [1] In this context, spin transition materials have shown great potential and aroused much interest [2,3,4,5]. When the surface-to-volume ratio increases, it results in an increasingly large effect on the thermal properties of SCO nanoparticles dominated by interactions between the surrounding environment and the molecules located on the edges (or surfaces). The molecules located on the surface (edge and corner) have specific properties because they interact with an external environment (matrix effect). The partition function of this inhomogeneous mean-field system comprising Nb , Nc , and Ne atoms belonging to the bulk, corner, and edge regions, respectively, is written as:.

Numerical Results and Discussion

Three Steps

Three States

Phase Diagram

Conclusions