Calculations of the susceptibility of interacting superparamagnetic particles
Calculations of the susceptibility of interacting superparamagnetic particles
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DOI：
10.1103/physrevb.63.024410
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发表时间：
2001-01-01
影响因子：
3.7
通讯作者：
Maylin, M
中科院分区：
文献类型：
--
作者：
Chantrell, RW;Walmsley, N;Maylin, M
本文提出了一个相互作用的超顺磁性粒子在固体基质中的分散体的磁特性模型。该模型使用蒙特卡罗技术，并能够预测的时间和温度依赖性的磁性。该模型被应用于钴颗粒系统的磁性行为，特别是低场磁化率的研究。结果表明，在高密度下，强相互作用系统表现出非朗之万行为，并给出磁化率随堆积密度的强非线性变化。初始磁化率的温度依赖性显示实验观察到的特征峰，峰值温度随堆积密度增加。研究了场冷（FC）和零场冷（ZFC）磁化。FC磁化强度的场依赖性取决于粒子间的相互作用，也取决于取向的易轴分布。FC磁化强度被发现表现出一个峰值，从相互作用。这种行为最终与系统的能垒分布（及其对相互作用的依赖性）有关，使用剩磁的温度衰减。它还表明，从完整的磁滞回线在每个温度下计算的剩磁不同的值通过增加系统的温度最初在饱和剩磁。作为磁状态和历史的函数的磁性质的演化指出了集体现象的重要性。自旋-自旋关联函数的计算表明，在低温下存在短程有序态。
A model of the magnetic properties of a dispersion of interacting superparamagnetic particles in a solid matrix is presented. The model uses Monte Carlo techniques and is capable of predicting the time and temperature dependence of the magnetic properties. The model is applied to the study of the magnetic behavior of a cobalt granular system, particularly the low-field susceptibility. It is shown that strongly interacting systems at high density exhibit non-langevin behavior and give a strongly nonlinear variation of susceptibility with packing density. The temperature dependence of the initial susceptibility shows the characteristic peak observed experimentally, with the peak temperature increasing with packing density. The field cooled (FC) and zero field cooled (ZFC) magnetization are also studied. The field dependence of the FC magnetization is shown to depend on the interparticle interactions and also on the orientational easy axis distribution. The FC magnetization is found to exhibit a peak resulting from the interactions. This behavior is finally related to the energy barrier distribution of the system (and its dependence on the interactions) using the temperature decay of remanence. It is also shown that the remanence calculated from the complete hysteresis loop at each temperature differs from the values obtained by increasing the temperature of a system initially at saturation remanence. The evolution of magnetic properties as a function of the magnetic state and history points to the importance of collective phenomena. Calculations of a spin-spin correlation function show the existence of a state with short-ranged order at low temperatures.