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arXiv 1310.3296cond-mat.stat-mech
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蜂窝晶格上自旋为3/2的Blume-Emery-Griffiths模型的相界

Phase boundaries of a spin-3/2 Blume-Emery-Griffiths model on a honeycomb lattice

M. Žukovič, M. Jaščur

摘要:

用蒙特卡罗模拟研究了蜂窝晶格上自旋为3/2的Blume-Emery-Griffiths模型,目的是确定模型参数范围内的相图,并研究各相之间的相变性质.对于正值的双二次双线性相互作用比$α$,我们发现两个铁磁有序相,F1和F2,与子晶格磁化强度(1/2,1/2)和(3/2,3/2),分别,我们的结果证实了有序-无序临界线的不连续字符作为单离子各向异性强度的函数,预测的有效场论(EFT)。对于负值的$α$,存在另一个亚铁磁(FRM)相,其类型为(1/2,3/2),位于F1和F2之间。然而,从EFT获得的大负$α$的有序-无序临界前沿的阶梯状变化没有再现,因此被认为是EFT近似的伪影。在各个确定的相位之间的各个点处进行的有限尺寸标度分析给出了与2D伊辛普适性类一致的临界指数$γ/ν$的比率,除了在边界交叉点附近,其中结果偏离标准值超过测量误差。

英文摘要:

The spin-3/2 Blume-Emery-Griffiths model on a honeycomb lattice is studied by Monte Carlo simulations with the goal to determine phase diagrams for a range of the model parameters and to investigate the nature of the phase transitions between the respective phases. For positive values of the biquadratic to bilinear interaction ratio $α$, we find two ferromagnetically ordered phases, F1 and F2, with the sublattice magnetizations (1/2,1/2) and (3/2,3/2), respectively, and our results confirm the discontinuous character of the order-disorder critical line as a function of the single-ion anisotropy strength, predicted by the effective-field theory (EFT). For negative values of $α$, there is another ferrimagnetic (FRM) phase of the type (1/2,3/2), located between F1 and F2. However, the step-like variation of the order-disorder critical frontier obtained from EFT for large negative $α$ is not reproduced and thus deemed artifact of the EFT approximation. Finite-size scaling analysis performed at various points between the respective identified phases gave the ratio of critical exponents $γ/ν$ consistent with the 2D Ising universality class, except in the vicinity of the boundary intersection, where the results deviated from the standard values beyond the measurement errors.

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