Monte Carlo study of low/high spin transitions
Monte Carlo study of low/high spin transitions
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低/高自旋跃迁的蒙特卡罗研究
DOI：
10.1007/bf01312791
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
K. Takahashi
中科院分区：
文献类型：
--
作者：
K. Takahashi
通过蒙特卡罗模拟研究了二维方形晶格上每个晶格位置有两个伊辛自旋的模型的有限温度性质。当一个点位上的伊辛自旋平行时，该点位称为高自旋态（HS），而当它们反平行时，该点位称为低自旋态（LS）。在整个研究中，推定HS的能量高于LS。在每个位点添加两个伊辛自旋形成一个总自旋，它通过自旋-自旋耦合与最近的总自旋相互作用。自旋-声子耦合也通过谐波弹簧引入，其弹簧常数和平衡距离取决于所涉及的位点的自旋状态。在这个系统中，我们通过改变温度来研究LS和HS之间的转变（称为低/高自旋转变（LHST））的特征。对于总自旋之间的铁磁相互作用，根据平均场计算，在纯自旋系统中可能发生二级相变：纯HS→HS和LS的混合态。晶格间距变化引起的晶格畸变对LHST：纯LS→（纯）HS起着至关重要的作用。在所研究的模型中，出现了强一阶相变的迹象，显示出明显的滞后。
We study the finite temperature property of a model on two dimensional square lattices with two Ising spins at each lattice site by Monte Carlo simulations. When those Ising spins at a lattice site are parallel the site is said to be in the high-spin state (HS), while when they are antiparallel the site is said to be in the low-spin state (LS). Throughout the study, the energy of HS is presumed to be higher than that of LS. Two Ising spins at each site are added to form a total spin, which interacts with its nearest neighbour total spins via spin-spin couplings. The spin-phonon coupling also is introduced via harmonic springs between nearest neighbour sites with spring constants and equilibrium distances depending on the spin states of the sites involved. In this system, we investigate the feature of transitions between LS and HS (to be called low/high spin transition (LHST)) by varying the temperature. As for the ferromagnetic interaction between total spins, the second order phase transition: pure HS→mixed state of HS and LS is possible to occur in a pure spin system, as is expected from mean field calculations. The role of lattice distortions by the change of lattice spacings is shown to be essential for LHST: pure LS→(pure)HS. In the model investigated, there appears an indication of the strong first order phase transition which reveals a conspicuous hysteresis.