磁性纳米颗粒系统偶极相互作用的Monte Carlo研究

doi:10.19596/j.cnki.1001-246x.7845

摘要/Abstract

摘要： 采用局域Monte Carlo方法模拟不同易轴分布的简单立方排列单分散单畴Fe纳米颗粒系统的ZFC-FC曲线及磁滞回线.结果表明：随着偶极相互作用的增强，系统的阻塞温度T_B逐渐增大，且ZFC曲线的峰变宽.说明偶极相互作用使得系统的有效能垒提高，分布宽度增加.研究FC曲线磁化强度的倒数与温度关系，发现偶极相互作用系统中存在反铁磁有序.系统的阻塞态及超顺磁态的磁滞回线表明，极低低温下，随着偶极相互作用的增强，系统的矫顽力和剩磁减小，偶极相互作用阻碍系统的磁化；系统处于超顺磁态，各向异性作用及偶极相互作用使得系统的磁化曲线偏离Langevin曲线且偶极相互作用展现出退磁相互作用效应.偶极相互作用增强，系统磁化曲线与Langevin曲线偏差量的最大值向低场移动.在偶极相互作用下，易轴与外场夹角为45°的磁性纳米颗粒系统的平均有效能垒和有效能垒分布宽度较易轴随机分布系统的大.

关键词: 磁性纳米颗粒, 偶极相互作用, Monte Carlo方法, Heisenberg模型

Abstract: Dipolar interactions of monodispersed single-domain Fe nanoparticles distributed in simple cubic lattice with different distribution of easy axes are studied with Monte Carlo method. Characteristic parameters of hysteresis loops and zero field cooled(ZFC)/field cooled(FC) magnetization curves are obtained. It is found that blocking temperature (T_B) increases and peaks of ZFC curves are broaden with increasing strength of dipolar interaction. It means that dipolar interactions increase height of effective energy barrier and broaden distribution of effective energy barrier of systems. Reciprocals of FC magnetizations as function of temperature shown that the curves follow Curie-Weiss law well above T_B. Curie-Weiss temperature (T₀) is zero for non-interacting system while it is negative for dipolar interacting system. Negative T₀ indicates that there is antiferromagnetic order in the interacting systems. Furthermore, with increasing strength of dipolar interaction, absolute value of T₀ for interacting system increases. Below blocking temperature, Hysteresis loops show that coercivity and remanence depend strongly on dipolar interaction. It is revealed that strong dipolar interactions suppress both coercivity and remanence of densely packed nanoparticles. Magnetization curves of superparamagnetic systems show that they are depressed with increasing particle packing density. Magnetization curves do not follow Langevin function and exhibit predominantly demagnetizing interacting effect. For interacting systems with 45° angle of applied field with easy axes, height of effective energy barrier are higher than those of random distribution systems, and distribution of effective energy barrier is wider than those of random distribution systems.

Key words: magnetic nanoparticle, dipolar interaction, Monte Carlo method, Heisenberg model

中图分类号:

O469
O737

莫康信, 苏佳佳. 磁性纳米颗粒系统偶极相互作用的Monte Carlo研究[J]. 计算物理, 2019, 36(3): 335-341.

MO Kangxin, SU Jiajia. Dipolar Interaction in Magnetic Nanoparticle Systems: A Monte Carlo Study[J]. CHINESE JOURNAL OF COMPUTATIONAL PHYSICS, 2019, 36(3): 335-341.

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