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首页> 外文期刊>Physica, B. Condensed Matter >Monte Carlo simulations of phase transitions and lattice dynamics in an atomphonon model for spin transition compounds
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Monte Carlo simulations of phase transitions and lattice dynamics in an atomphonon model for spin transition compounds

机译：自旋跃迁化合物的原子声子模型中相变和晶格动力学的蒙特卡罗模拟

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摘要

We apply here the Monte Carlo Metropolis method to a known atomphonon coupling model for 1D spin transition compounds (STC). These inorganic molecular systems can switch under thermal or optical excitation, between two states in thermodynamical competition, i.e. high spin (HS) and low spin (LS). In the model, the ST units (molecules) are linked by springs, whose elastic constants depend on the spin states of the neighboring atoms, and can only have three possible values. Several previous analytical papers considered a unique average value for the elastic constants (mean-field approximation) and obtained phase diagrams and thermal hysteresis loops. Recently, Monte Carlo simulation papers, taking into account all three values of the elastic constants, obtained thermal hysteresis loops, but no phase diagrams. Employing Monte Carlo simulation, in this work we obtain the phase diagram at T=0 K, which is fully consistent with earlier analytical work; however it is more complex. The main difference is the existence of two supplementary critical curves that mark a hysteresis zone in the phase diagram. This explains the pressure hysteresis curves at low temperature observed experimentally and predicts a "chemical" hysteresis in STC at very low temperatures. The formation and the dynamics of the domains are also discussed.
机译：我们在这里将Monte Carlo Metropolis方法应用于一维自旋跃迁化合物（STC）的已知原子声子耦合模型。这些无机分子系统可以在热力学竞争的两种状态下，即高自旋（HS）和低自旋（LS），在热或光激发下切换。在该模型中，ST单元（分子）由弹簧连接，弹簧的弹性常数取决于相邻原子的自旋状态，并且只能具有三个可能的值。先前的几篇分析论文都考虑了弹性常数的唯一平均值（平均场近似），并获得了相图和热滞回线。最近，Monte Carlo模拟论文考虑了弹性常数的所有三个值，获得了热滞回线，但没有相位图。使用蒙特卡洛模拟，在这项工作中，我们获得了T = 0 K时的相图，这与早期的分析工作完全一致。但是它更复杂。主要区别在于存在两条补充临界曲线，它们在相图中标记了一个磁滞区。这解释了通过实验观察到的低温下的压力滞后曲线，并预测了在非常低的温度下STC中的“化学”滞后。还讨论了域的形成和动力学。

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