Metastable states in the triangular-lattice Ising model studied by Monte Carlo simulations: Application to the spin-chain compound Ca 3 Co 2 O 6
Metastable states in the triangular-lattice Ising model studied by Monte Carlo simulations: Application to the spin-chain compound Ca 3 Co 2 O 6
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DOI：
10.1103/physrevb.79.184422
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发表时间：
2009-05
影响因子：
3.7
通讯作者：
R. Soto;G. Martínez;M. N. Baibich;J. M. Florez;P. Vargas
中科院分区：
文献类型：
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作者：
R. Soto;G. Martínez;M. N. Baibich;J. M. Florez;P. Vargas
已知自旋链化合物Ca3Co2O6在低温下的磁化强度随磁场的变化呈现出非常有趣的平稳期。它们的起源至今仍有争议。本文研究了该化合物在三角形晶格上的单翻转蒙特卡罗模拟，并证明了亚稳态对铁磁1/3平台在10 K以下分裂的决定性影响。我们认为[Co2O6]n链是由开放边界条件下平面团簇上的大伊辛自旋描述的巨磁矩。利用这个简单的冻结矩模型，得到了不同扫速下的阶梯磁化曲线，与实验结果吻合较好。我们特别描述了将低温1/3平台分成三步的非平衡状态。它们热弛豫到1/3平台，在平衡处有长程阶。这些状态被进一步分析与快照揭示了一个域墙结构，负责观察到的1/3平台的行为。并将小三角簇的精确结果与我们的蒙特卡罗结果进行了比较，为该化合物的热描述提供了进一步的支持。
It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting plateaus in the magnetization as a function of the magnetic field at low temperatures. The origin of them is still controversial. In this paper we study the thermal behavior of this compound with a single-flip Monte Carlo simulation on a triangular lattice and demonstrate the decisive influence of metastable states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We consider the [Co2O6]n chains as giant magnetic moments described by large Ising spins on planar clusters with open boundary conditions. With this simple frozen-moment model we obtain stepped magnetization curves which agree quite well with the experimental results for different sweeping rates. We describe particularly the out-of-equilibrium states that split the low-temperature 1/3 plateau into three steps. They relax thermally to the 1/3 plateau, which has long-range order at the equilibrium. Such states are further analyzed with snapshots unveiling a domain-wall structure that is responsible for the observed behavior of the 1/3 plateau. A comparison is also given of the exact results in small triangular clusters with our Monte Carlo results, providing further support for our thermal description of this compound.