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

Gudyma IV, Maksymov AIu, Ivashko VV - Nanoscale Res Lett (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of General Physics, Chernivtsi National University, Kotsjubynskyi Str. 2, 58012, Chernivtsi, Ukraine, yugudyma@gmail.com.

ABSTRACT
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.

No MeSH data available.


The thermal transition curves for fixed values of external applied pressure. The system’s parameters are the following: g=150, Δ=1,000 K, L=40. Here, the black curves correspond to the system without pressure; the red, blue, and pink ones are for the system with values pΔV=100 K, pΔV=300 K, and pΔV=600 K, respectively.
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Fig1: The thermal transition curves for fixed values of external applied pressure. The system’s parameters are the following: g=150, Δ=1,000 K, L=40. Here, the black curves correspond to the system without pressure; the red, blue, and pink ones are for the system with values pΔV=100 K, pΔV=300 K, and pΔV=600 K, respectively.

Mentions: The behavior of spin-crossover system under applied external pressure was examined basing on the transition curves obtained from Monte Carlo simulations of Hamiltonian (4). The corresponding results are reported in Figure 1. For simulations hereinafter, we chose the Boltzmann constant kB=1 (in Planck units) and the following system parameters: g=150, Δ=1,000 K, L=40, and 1,000 Monte Carlo steps per Kelvin degree. The product of the external pressure p and the change of molecular volume ΔV will measure in energy units of T similar to ref. [17]. Further, we postulated this product as pressure action because the volume change cannot be different in specific spin crossover material and this product may be changed only by variation of pressure p. The black curves in Figure 1 indicate pressureless system for spin-spin interaction J=145 K which is sufficient for thermal hysteresis. This value of spin-spin interaction is the same also for other curves from the figure. The red, blue, and pink curves are obtained for the pressure values pΔV=100 K, pΔV=300 K, and pΔV=600 K, respectively. Taking into account that for transition to HS state, the metal-ligand bounds increase and the action of external pressure prevents the bounds lengthening and increase the energy gap between the spin states; therefore, it leads to the shifting of the transition curves toward higher temperatures. The shifting of transition curves may be clearly observed from Figure 1 as the result of pressure increasing together with the vanishing of hysteresis width which takes place at the same time. If we turn to the standard units, it may be observed that the transition temperatures shift to the higher values with 20 K/kbar. This is in agreement with the experimental and theoretical data already reported in the paper [18]. Referring to the phase diagram, it is obvious that the influence of sufficient high external pressure moves the system on the phase diagram from the region of first-order phase transition to the region of second-order phase transition [12, 19, 20].Figure 1


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

Gudyma IV, Maksymov AIu, Ivashko VV - Nanoscale Res Lett (2014)

The thermal transition curves for fixed values of external applied pressure. The system’s parameters are the following: g=150, Δ=1,000 K, L=40. Here, the black curves correspond to the system without pressure; the red, blue, and pink ones are for the system with values pΔV=100 K, pΔV=300 K, and pΔV=600 K, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494018&req=5

Fig1: The thermal transition curves for fixed values of external applied pressure. The system’s parameters are the following: g=150, Δ=1,000 K, L=40. Here, the black curves correspond to the system without pressure; the red, blue, and pink ones are for the system with values pΔV=100 K, pΔV=300 K, and pΔV=600 K, respectively.
Mentions: The behavior of spin-crossover system under applied external pressure was examined basing on the transition curves obtained from Monte Carlo simulations of Hamiltonian (4). The corresponding results are reported in Figure 1. For simulations hereinafter, we chose the Boltzmann constant kB=1 (in Planck units) and the following system parameters: g=150, Δ=1,000 K, L=40, and 1,000 Monte Carlo steps per Kelvin degree. The product of the external pressure p and the change of molecular volume ΔV will measure in energy units of T similar to ref. [17]. Further, we postulated this product as pressure action because the volume change cannot be different in specific spin crossover material and this product may be changed only by variation of pressure p. The black curves in Figure 1 indicate pressureless system for spin-spin interaction J=145 K which is sufficient for thermal hysteresis. This value of spin-spin interaction is the same also for other curves from the figure. The red, blue, and pink curves are obtained for the pressure values pΔV=100 K, pΔV=300 K, and pΔV=600 K, respectively. Taking into account that for transition to HS state, the metal-ligand bounds increase and the action of external pressure prevents the bounds lengthening and increase the energy gap between the spin states; therefore, it leads to the shifting of the transition curves toward higher temperatures. The shifting of transition curves may be clearly observed from Figure 1 as the result of pressure increasing together with the vanishing of hysteresis width which takes place at the same time. If we turn to the standard units, it may be observed that the transition temperatures shift to the higher values with 20 K/kbar. This is in agreement with the experimental and theoretical data already reported in the paper [18]. Referring to the phase diagram, it is obvious that the influence of sufficient high external pressure moves the system on the phase diagram from the region of first-order phase transition to the region of second-order phase transition [12, 19, 20].Figure 1

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of General Physics, Chernivtsi National University, Kotsjubynskyi Str. 2, 58012, Chernivtsi, Ukraine, yugudyma@gmail.com.

ABSTRACT
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.

No MeSH data available.