Nanocomposites and nanomaterials
Monte Carlo modeling of spin crossover nanomaterial within Ising-like model
Ivashko V.V.1
1 Department of Correlation Optics, Yuriy Fedkovych Chernivtsi National University, Kotsjubynskyi str., 2, Chernivtsi-58012, Ukraine.
E-mail: v.ivashko@chnu.edu.ua

The development of nanotechnology to a large extent depends on the current state of its elemental base. Due to their extraordinary properties spin crossover compounds (SCO) are promising materials for nanotechnology [1, 2]. There feature lies in the possibility of a spin transition between Low-Spin (LS) and High-Spin (HS) states.
We investigated the microscopic behavior of 2D hexagonal spin-crossover nanosystem based on the following general form of Ising-like Hamiltonian:
                          (1)
Where si is the pseudospin of each i site (i = 1, 2, ..., N), scalar variable which take values ±1 for HS and LS states respectively, J is the interaction constant between two neighboring spins (i and j) and h is the external field. Here h (related to transition metal ion) is defined as:
                      (2)
Where Δ is the ligand field splitting energy, describing the energy difference between HS and LS states, kB is the Boltzmann constant, T is the absolute temperature, g is the degeneracy ratio between HS and LS states, p is the external pressure and ΔV is the molecular volume change, caused by the spin transition.
According to our results of Monte Carlo simulation of the Hamiltonian (1), a relation between the system size and interaction strength J between neighbor SCO molecules, was establish. Possibility of tuning the thermal hysteresis by using the external pressure, was obtained. The influence of defects on the nanosystem, was studied. The obtained results are in agreement with the experimental.

1.	Spin-crossover materials: properties and applications, edited by         M. A. Halcrow (Wiley, Chichester, 2013).
2.	Spin crossover in transition metal compounds I-III, topics in current chemistry vol. 233-234, edited by P. Gütlich and H. Goodwin (Springer-Verlag, Berlin/Heidelberg, 2004).