Structures of Metastable States in Phase Transitions with a High-Spin Low-Spin Degree of Freedom
Structures of Metastable States in Phase Transitions with a High-Spin Low-Spin Degree of Freedom
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DOI：
10.1143/ptp.114.719
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发表时间：
2005-07
影响因子：
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通讯作者：
S. Miyashita;Y. Konishi;H. Tokoro;M. Nishino;K. Boukheddaden;F. Varret
中科院分区：
文献类型：
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作者：
S. Miyashita;Y. Konishi;H. Tokoro;M. Nishino;K. Boukheddaden;F. Varret
低自旋(LS)和高自旋(HS)态简并度的不同导致了自旋交叉原子组成的材料中自旋交叉相变和电荷转移相变的有趣的熵效应。用Wajnflasz模型研究了自旋-交叉(SC)相变的机制，其中考虑了自旋态(HS或LS)的简并，并很好地描述了自旋-交叉相变的协同性质。最近，利用推广的Wajnflasz模型研究了LS和HS格点之间由于电子跃迁引起的电荷转移相变。含有SC和CT的体系都具有高温结构(HT)和低温结构(LT)，它们之间的相变可以是光滑的交叉，也可以是不连续的一阶相变，这取决于系统的参数值。尽管标准SC系统和CT系统显然有很大的不同，但事实证明，在一定的变量变换下，两个模型是等价的。在这两个系统中，低温下亚稳态的结构是一个令人感兴趣的问题。我们在一个统一的模型中系统地研究了HT组分的温度依赖性，发现了该模型的几种平衡和亚稳态结构，它们是系统参数的函数。特别是，我们在低温区发现了高温超导体的折返型亚稳分支，这将对相关材料的光辐照过程的研究起到重要作用。
The difference in the degeneracy of low-spin (LS) and high-spin (HS) states causes interesting entropy effects on spin-crossover phase transitions and charge transfer phase transitions in materials composed of spin-crossover atoms. Mechanisms of the spin-crossover (SC) phase transitions have been studied using the Wajnflasz model, where the degeneracy of the spin states (HS or LS) is taken into account, and the cooperative nature of the spin-crossover phase transitions has been well described. Recently, a charge transfer (CT) phase transition due to electron hopping between LS and HS sites has been studied using a generalized Wajnflasz model. Systems with SC and CT both have a high temperature structure (HT) and a low temperature structure (LT), and the transition between them can be a smooth crossover or a discontinuous first-order phase transition, depending on the parameter values of the systems. Although, apparently, the standard SC system and the CT system are very different, it lias been shown that the two models are equivalent under a certain transformation of variables. In both systems, the structure of the metastable state at low temperatures is a matter of interest. We study the temperature dependence of the fraction of HT systematically in a, unified model and find several structures of equilibrium and metastable states of the model as functions of the system parameters. In particular, we find a reentrant-type metastable branch of HT in a low temperature region, which sould play an important role in the study of the photo-irradiated processes of related materials.