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Iu. Gudyma et al.
dia- or paramagnetism. The cooperative behavior of the spin transition in the
solid spin-crossover materials demands an interaction between their molecules.
The largest class of SCO complexes are the Fe(II) SCO complexes. In octahedral
symmetry O h , the ferrous iron molecular complexes can be converted between
diamagnetic LS (e 0
g t 6
2g ) and paramagnetic HS (e 2
g t 4
2g ) states, which leads to a
significant change in the metal-ligand bond length. SCO materials are known to have
potential applications such as reversible high-density memories, ultrafast switches
(at the nanoscale), sensors of temperature and pressure, fundamental elements in
display technologies, etc. Consequently SCO systems have been studied extensively
both theoretically and experimentally. We will not here recall all the properties of
the SCO systems, since extensive literature exists on the subject (see, e.g., [1–5]).
If solids shrink to the nanoscale, the surface-to-volume ratio increases, and
the surface-environment interaction becomes a major factor for affecting material behavior. The control over functionalities at the nanoscale (in nanoparticles,
nanopatterns, thin films, and, ultimately, single molecules) appears as a cornerstone
in the elaboration of advanced materials for many very important above technologies. The individual nanoparticles possessing an abrupt transition with a thermal
hysteresis loop are appealing because they can be used for information storage
at the nanometric level. Such effects are ambiguous or beneficial, depending on
environmental conditions and material application. These properties are very sensitive to changes in external environment. The surface exhibits some disorganized
fluctuations which usually are ascribed to environmental randomness [6]. However
the rational control of the behavior of these materials on a nanometric scale is
highly required, especially when they are integrated into functional devices. The
investigation of surface-environment effects can be realized by modern experiments
with a comprehensive suite of surface-sensitive spectroscopy and microscopy
tools [7]. One of the major challenges of modern technology is to stabilize
the nanoparticles and the surface in order to minimize its interaction with the
environment. It is obvious that surface-environment distribution can be neglected in
the thermodynamic limit, but on the other hand, a molecule must always be viewed
as part of its environment [8].
The current review addresses mainly the role of surface-environment effects of
spin-crossover nanocrystals in the occurrence of phase transition in the material.
The important issue is to understand the interplay of cooperativity of the system and
the fluctuations of its environment. It is almost obvious that molecules on surfaces
have different SCO properties than the inner molecules [6, 9]. This may influence
the properties of the whole particle in this very low size range [10]. The transition
metal ions can be seriously altered at the surface of the particle. It is very likely,
particularly in the case of small particles with high specific surface areas, that these
Fe(II) ions “feel” considerable differences in bond strength or even suffer from
coordinative defects and consequently do not exhibit SCO [11]. We are interested
in phenomena that are associated with the emergence of disorganized random
fluctuations in the state of the system under influence of surrounding environment.
This chapter is organized as follows: In Sect. 27.2, we outline the Hamiltonian and
its application to the Ising-like model of spin-crossover nanocrystal interacting with
the surroundings; in Sect. 27.3, we discuss the results; and finally, in Sect. 27.4, we
present our conclusions.
Iu. Gudyma et al.
dia- or paramagnetism. The cooperative behavior of the spin transition in the
solid spin-crossover materials demands an interaction between their molecules.
The largest class of SCO complexes are the Fe(II) SCO complexes. In octahedral
symmetry O h , the ferrous iron molecular complexes can be converted between
diamagnetic LS (e 0
g t 6
2g ) and paramagnetic HS (e 2
g t 4
2g ) states, which leads to a
significant change in the metal-ligand bond length. SCO materials are known to have
potential applications such as reversible high-density memories, ultrafast switches
(at the nanoscale), sensors of temperature and pressure, fundamental elements in
display technologies, etc. Consequently SCO systems have been studied extensively
both theoretically and experimentally. We will not here recall all the properties of
the SCO systems, since extensive literature exists on the subject (see, e.g., [1–5]).
If solids shrink to the nanoscale, the surface-to-volume ratio increases, and
the surface-environment interaction becomes a major factor for affecting material behavior. The control over functionalities at the nanoscale (in nanoparticles,
nanopatterns, thin films, and, ultimately, single molecules) appears as a cornerstone
in the elaboration of advanced materials for many very important above technologies. The individual nanoparticles possessing an abrupt transition with a thermal
hysteresis loop are appealing because they can be used for information storage
at the nanometric level. Such effects are ambiguous or beneficial, depending on
environmental conditions and material application. These properties are very sensitive to changes in external environment. The surface exhibits some disorganized
fluctuations which usually are ascribed to environmental randomness [6]. However
the rational control of the behavior of these materials on a nanometric scale is
highly required, especially when they are integrated into functional devices. The
investigation of surface-environment effects can be realized by modern experiments
with a comprehensive suite of surface-sensitive spectroscopy and microscopy
tools [7]. One of the major challenges of modern technology is to stabilize
the nanoparticles and the surface in order to minimize its interaction with the
environment. It is obvious that surface-environment distribution can be neglected in
the thermodynamic limit, but on the other hand, a molecule must always be viewed
as part of its environment [8].
The current review addresses mainly the role of surface-environment effects of
spin-crossover nanocrystals in the occurrence of phase transition in the material.
The important issue is to understand the interplay of cooperativity of the system and
the fluctuations of its environment. It is almost obvious that molecules on surfaces
have different SCO properties than the inner molecules [6, 9]. This may influence
the properties of the whole particle in this very low size range [10]. The transition
metal ions can be seriously altered at the surface of the particle. It is very likely,
particularly in the case of small particles with high specific surface areas, that these
Fe(II) ions “feel” considerable differences in bond strength or even suffer from
coordinative defects and consequently do not exhibit SCO [11]. We are interested
in phenomena that are associated with the emergence of disorganized random
fluctuations in the state of the system under influence of surrounding environment.
This chapter is organized as follows: In Sect. 27.2, we outline the Hamiltonian and
its application to the Ising-like model of spin-crossover nanocrystal interacting with
the surroundings; in Sect. 27.3, we discuss the results; and finally, in Sect. 27.4, we
present our conclusions.