Artur Maksymov

Study of pressure influence on thermal transition in spin-crossover nanomaterials

The thermal transition accompanied by the variation of the molecular volume in nanoparticles of spin-crossover materials has been studied on the basis of microscopic Ising-like model solved using Monte Carlo methods. For considered model, we examined the spin-crossover phenomenon with applied hydrostatic pressure and thus was shown the possibility to shift transition temperature toward its room value. The obtained results of numerical simulations are in agreement with the experimental ones.

Kinetics of Nonequilibrium Transition in Spin-Crossover Compounds

This chapter is devoted to an analysis of spin-crossover system dynamics in the framework of Ising-like mechanoelastic model and macroscopic phenomenological model. Based on mechanoelastic model, the intermolecular interaction between spin-crossover sites and cooperative effects in materials has been studied. For light-induced spin-transition the relaxation curves has been calculated by Monte Carlo methods. The additive and multiplicative noise influence on transition phenomena following from system contact with environment was found within macroscopic description of spin-crossover system dynamics in Langevin framework and the corresponding Fokker-Planck equation. The mean first passage time from metastable state driven by colored noise was calculated by using the Kramers-like approximation. In addition, it is shown that transitions can be controlled by a parameter that governs relaxation flow, intensity of light and noise intensity.

Optically induced switching in spin-crossover compounds: microscopic and macroscopic models and their relationship.

We present the examination of light induced behavior of spin-crossover compounds. We focus on the switching phenomena between low-spin and high-spin states of the system. The connection between the Ising-like model and the macroscopic evolution equation has been analyzed. By means of numerical simulations, we found the dynamical potential changes, the corresponding light induced hysteresis, and the transient regimes. The statistical properties of the system in contact with a heat bath are shown in a stationary probability distribution.

Cooperative Phenomena in Spin-Crossover Molecular Crystals

In this chapter, we focus on the study of influence of surface on thermal-induced spin-crossover phenomenon which is a subject of a broad and current interest. The modified Ising-like model of spin-crossover solids with the ligand field as function of the molecule positions and random component on the surface has been proposed. By means of the adapted Metropolis Monte Carlo algorithm, the thermal spin transition curves were calculated. The detailed kinetics of switching between high-spin and low-spin molecules have been analyzed from spin configuration at transition temperature, which gives a general idea about contribution of molecules from the surface and inside the lattice into resulting magnetization of the systems. The behavior of hysteresis loop for various surface coupling and fluctuation strengths has been described.

Temperature dependence of exchange bias in (NiFe/IrMn)n multilayer films studied through static and dynamic techniques

The in-plane temperature dependence of exchange bias was studied through both dc magnetometry and ferromagnetic resonance spectroscopy in a series of [NiFe/IrMn]n multilayer films, where n is the number of layer repetitions. Major hysteresis loops were recorded in the temperature range of 300 K to 2 K to reveal the effect of temperature on the exchange bias in the static regime while temperature-dependent continuous-wave ferromagnetic resonance for frequencies from 3 to 16 GHz was used to determine the exchange bias dynamically. Strong divergence between the values of exchange bias determined using the two different types of measurements as well as a peak in temperature dependence of the resonance linewidth were observed. These results are explained in terms of the slow-relaxer mechanism.

Phenomenological Models of Photoinduced Transition in Spin-Crossover Materials

The stochastic kinetics of photoinduced transition in spin-crossover systems, as representatives of synthetic molecular magnetic materials, was reviewed. The focus has been done on the macroscopic phenomenological models, which were described by dynamic potential in terms of Lyapunov functions and obeys to Langevin kinetics with white and colored stochastic processes. By corresponding Fokker–Planck equation was studied the evolution of probability of system states. For the system with light-induced transition which is additionally driven by external periodic force it has been shown the possibility of resonance enhancement of magnetization at certain values of the amplitude of periodic signal and noise intensity. The stochastic resonance phenomenon was analyzed by signal-to-noise ratio for Markovian and non-Markovian noise, various amplitudes and frequencies of periodic signal, and also variation of noise intensity.

Light-induced transition in spin-crossover compounds with correlated stochastic processes

The stochastic kinetics of a photoinduced phase transition in spin-crossover compounds in the presence of environmental background and systems internal noises were studied. The correlation phenomena that determine the color of internal and external noises was taken into account. The mathematical framework for the study of light-induced transition in spin-crossover nanoparticles was based on the Langevin equation and steady solution of corresponding Fokker-Planck equation. The system behavior was described by nonequilibrium (dynamic) potential in terms of Lyapunov functions for the deterministic case and by stochastic Fokker-Planck potential in the noise case action.