发表机构
Nanjing University of Science and Technology（南京理工大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过大规模蒙特卡洛模拟揭示二维海森堡磁体中自旋对称性影响有限温度相变，特征温度偏离BKT理论源于涡旋-反涡旋对增殖的熵增益。
AI 中文摘要
近年来，本征二维（2D）磁体的进展产生了对跨不同自旋对称性类别的有限温度相变进行统一理解的需求。在此，我们利用大规模蒙特卡洛模拟研究经典二维海森堡模型中的有限温度磁性，连续跨越易平面、各向同性和易轴区域。我们发现特征温度受到有限尺寸效应与自旋对称性相互作用的强烈影响，这种相互作用由磁晶各向异性诱导，在各向同性海森堡区域最为显著，而在向易平面和易轴极限过渡时显著减弱。在易平面区域考察Berezinskii–Kosterlitz–Thouless（BKT）物理时，我们发现从磁化强度和热容独立估计的特征温度与BKT理论提出的值显著偏离，但与先前报道的XY模型中的异常相符。我们报告特征温度反而与涡旋-反涡旋对的增殖相关，表明其加速成核带来的熵增益是该异常的起源。通过理论和数值两方面建立这一联系，我们认为有限易平面海森堡磁体中的热力学特征温度，包括与BKT理论的偏离，受限于有限尺寸自旋关联与涡旋增殖之间的相互作用。这些结果阐明了在有限二维磁体中，实验和技术相关的温度尺度如何随磁各向异性、自旋对称性和系统尺寸演变。
英文摘要
Recent advances in intrinsic two-dimensional (2D) magnets have created a need for a unified understanding of finite-temperature phase transitions across different spin-symmetry classes. Here, we investigate finite-temperature magnetism in the classical 2D Heisenberg model using large-scale Monte Carlo simulations, continuously spanning the easy-plane, isotropic, and easy-axis regimes. We find that characteristic temperatures are strongly affected by the interplay of finite-size effects and spin symmetry, induced by magnetocrystalline anisotropy, being most pronounced in the isotropic Heisenberg regime and substantially reduced toward the easy-plane and easy-axis limits. Examining Berezinskii--Kosterlitz--Thouless (BKT) physics in the easy-plane regime, we find that the characteristic temperatures independently estimated from the magnetization and heat capacity deviate significantly from those proposed by BKT theory, but match a previously reported anomaly in the XY-model. We report that characteristic temperatures instead are correlated with the proliferation of vortex-antivortex pairs, suggesting the gain in entropy by their accelerated nucleation as the origin of the anomaly. Establishing this connection both theoretically and numerically, we argue that the thermodynamic characteristic temperature in finite easy-plane Heisenberg magnets, including the deviation from BKT theory, is subject to the interplay between finite-size spin correlations and vortex proliferation. These results clarify how experimental and technologically relevant temperature scales evolve with magnetic anisotropy, spin symmetry, and system size in finite 2D magnets.
Comments11 pages, 5 figures
