Nanocomposites and nanomaterials

Thermal induced transition in 3D spin-crossover lattice with (anti)ferromagnetic surface under external fluctuations
Gudyma Iu.V.1, Maksymov A.Iu.2
1 Institute of Physical, Technical and Computer Sciences, Yuriy Fedkovych Chernivtsi National University, 2 Kotsjubynskyi Str., Chernivtsi 58012, Ukraine.
E-mail: yugudyma@gmail.com
2 Marian Smoluchowski Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Krakow, Poland

The spin-crossover (SCO) compounds are the transition coordination complexes with pseudo-octahedral symmetry containing metal ion surrounded by a ligand. Under external stimuli the SCO molecule can show a transition between intrinsic low-spin and high-spin states which may exhibit different magnetic, optical, electric and other properties. In our work, the SCO Ising-like model, widely used for studying SCO complexes, is completed by the different interaction energies in a bulk and on a surface of a SCO nanocrystal that could play crucial role in explanation the experimental results. For studying the influence of surface’s molecules, we split the interaction term into three separate couplings. The Hamiltonian of the model is following [1]:
, 		(1)
where, Js,bs,b is short-range couplings between nearest neighbor sites: the one describing the coupling of molecules on the surface (Js), the second one that is responsible for linking the bulk of nanocrystal with its surface (Jbs), and the last one describing the interaction of bulk molecules (Jb). Here, hi is time dependent external field that includes degenerate of states and fluctuations.
The properties of the system were analyzed by Monte Carlo simulations, based on Metropolis algorithm. It was shown the shifting of transition temperatures contributed by cooperativity of surface molecules in SCO system under fluctuations. Also, we found that the nature of cooperativity for the sites on the surface has the drastic impact on the completeness of phase transition. The obtained results agree with experimental data.

1.	Gudyma I., Maksymov A. The cooperativity in 3D spin-crossover nanocrystals with ferromagnetic and antiferromagnetic surface // Appl. Surf. Sci.-2019. – 483. P. 779-784.