Nanocomposites and nanomaterials

The transition in finite size spin-crossover system with fluctuating external filed
Gudyma Iu.V.1, Maksymov A.Iu.2
1 Department of General Physics, Yuriy Fedkovych Chernivtsi National University. Kotsyubynsky, 2, Chernivtsi-58012, Ukraine
E-mail: yugudyma@gmail.com
2 Atomic Optics Department, Marian Smoluchowski Institute of Physics, Jagiellonian University, Łojasiewicza, 11, Kraków-30-348, Poland.

In this work we study a magnetic spin-crossover nanosystem in the framework of microscopic Ising-like model with finite size, taking into account the energy perturbations of the external field, relative to transition metal ion [1]. The important issue is to understand the influence of finite size effects and fluctuations strength of ligand field on the hysteretic properties of the spin-crossover system.
The behavior of spin-crossover compounds at molecular level is described by the microscopic Ising-like model in the framework of mean field approach with the intermolecular interaction with the following Hamiltonian [1]: 
, 		(1)
 is a pseudospin scalar variable taking the values ±1 depending which of stable state is realized,  is the intersites coupling,  is external effective field determined by energy gap between stable states , the temperature  and the degeneracy ratio  between system’s state ( is Boltzmann constant). Here,  is the fluctuations that randomize the external local field. In current model we consider only Gaussian white fluctuations.
Based on the provided Ising-like Hamilotian we obtained the transition curves for 2D and 3D spin-crossover magnetic nanoparticles, in framework of breathing crystal field concept [2]. The detailed description of the dependencies of hysteresis width on the size effects and the strength of statistical fluctuations were obtained. 

1.	Gudyma Iu., Maksymov A., Spinu L. Size effects in spin-crossover nanoparticles in framework of 2D and 3D Ising-like breathing crystal field model // Appl. Surf. Sci.-2015.-352.-P.60-65.
2.	Gudyma Iu., Maksymov A., Enachescu C. Phase transition in spin-crossover compounds in the breathing crystal field model // Phys. Rev. B.-2014.- 89, 224412.