arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2007.02230cond-mat.mes-hallphysics.atm-clusphysics.comp-ph
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铁纳米团簇的尺寸和温度相关磁化强度

Size and temperature dependent magnetization of iron nanoclusters

G. Dos Santos, R. Aparicio, D. Linares, E. N. Miranda, J. Tranchida, G. M. Pastor, E. M. Bringa

摘要:

采用自旋动力学(SD)与分子动力学(MD-SD)耦合的方法研究了体心立方结构铁纳米团簇的磁性行为。的总磁化强度以及自由表面和表面/核心的纳米团簇的比例的影响中的铁磁尺寸效应进行了详细的分析,在很宽的温度范围内,超越了集群和体居里温度。与实验数据和理论模型的基础上的平均场伊辛模型适合于小集群,并考虑到低协调自旋在自由表面的影响进行比较。我们的每个原子的平均磁化强度M(T)的温度依赖性的结果,包括跨晶格自由度的热化,是非常好的协议与现有的实验测量小铁纳米团簇。相反,如果平移自由度被人为冻结,则观察到与实验的显著差异。在居里温度附近,M(T)的有限尺寸效应尤为重要。居里温度以上的模拟磁化与团簇大小的模型预测假设短程磁有序(SRMO)。解析近似的磁化强度作为温度和尺寸的函数。

英文摘要:

The magnetic behavior of bcc iron nanoclusters, with diameters between 2 and 8 nm, is investigated by means of spin dynamics (SD) simulations coupled to molecular dynamics (MD-SD), using a distance-dependent exchange interaction. Finite-size effects in the total magnetization as well as the influence of the free surface and the surface/core proportion of the nanoclusters are analyzed in detail for a wide temperature range, going beyond the cluster and bulk Curie temperatures. Comparison is made with experimental data and with theoretical models based on the mean-field Ising model adapted to small clusters, and taking into account the influence of low coordinated spins at free surfaces. Our results for the temperature dependence of the average magnetization per atom M(T), including the thermalization of the transnational lattice degrees of freedom, are in very good agreement with available experimental measurements on small Fe nanoclusters. In contrast, significant discrepancies with experiment are observed if the translational degrees of freedom are artificially frozen. The finite-size effects on M(T) are found to be particularly important near the cluster Curie temperature. Simulated magnetization above the Curie temperature scales with cluster size as predicted by models assuming short-range magnetic ordering (SRMO). Analytical approximations to the magnetization as a function of temperature and size are proposed.

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