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首页> 外文期刊>Physica, A. Statistical mechanics and its applications >Transition from superparamagnetism to ferromagnetic single-domain in a Heisenberg model for nano-cluster magnetic system
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Transition from superparamagnetism to ferromagnetic single-domain in a Heisenberg model for nano-cluster magnetic system

机译：海森堡模型中纳米团簇磁性系统从超顺磁性到铁磁性单畴的转变

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The transition behaviour of a magnetic system consisting of numerous nano-sized clusters with a zero external field was studied. We investigated the transition from superparamagnetism (SP) to ferromagnetic single-domain (SD) state due to the increase of cluster size by Monte Carlo simulation of Heisenberg and Ising models which are the two extreme cases in anisotropy of spin exchange. The counter-effect of uniaxial anisotropy energy against thermal activation plays an important role in determining the degree of polarization of magnetic moments along easy axis as well as the total anisotropic energy of the system. Based on the sigmoidal anisotropic energy dependence on cluster size, we studied the relationship of the dynamic growth exponent P and critical cluster size Nc of the transition with reduced temperature t and uniaxial anisotropic constant A. We found that the transitional growth exponent P, exhibiting a maximum at certain temperature, is not a universal constant as some previous investigators suggested. (C) 2000 Published by Elsevier Science B.V. All lights reserved. [References: 22]
机译：研究了由许多纳米簇和零外场组成的磁系统的跃迁行为。我们通过自旋交换各向异性的两种极端情况的Heisenberg和Ising模型的蒙特卡罗模拟研究了由于团簇尺寸增加而导致的从超顺磁性（SP）到铁磁单畴（S​​D）状态的转变。单轴各向异性能量对热活化的反作用在确定沿易轴的磁矩的极化程度以及系统的总各向异性能量方面起着重要作用。基于S形各向异性能量对簇尺寸的依赖性，我们研究了过渡态的动态增长指数P和临界簇尺寸Nc与降低的温度t和单轴各向异性常数A的关系。我们发现过渡增长指数P呈现出a在某些温度下的最大值不是某些先前研究人员所建议的通用常数。 （C）2000，Elsevier Science B.V.保留所有照明。 [参考：22]

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