Computational model of the magnetic and transport properties of interacting fine particles
Computational model of the magnetic and transport properties of interacting fine particles
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DOI：
10.1103/physrevb.65.174417
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发表时间：
2002-05-01
影响因子：
3.7
通讯作者：
Stancu, A
中科院分区：
文献类型：
--
作者：
Verdes, C;Ruiz-Diaz, B;Stancu, A
应用计算模型研究了单区粒子相互作用系统的磁滞特性。该模型基于蒙特卡罗方法，同时考虑了静磁和交换作用。结果集中在详细研究了Co粒子的行为，相互作用强度随堆积密度的变化而变化。结果表明，磁特性强烈依赖于参数β=KV/KT，其中K为各向异性常数，V为平均粒子体积。对于小贝塔--即接近超顺磁性系统--的微观结构是由磁通闭合的趋势主导的。然而，这种相互作用导致局域能垒的增加，导致H-c和堆积密度的增加。对于大的β，各向异性和静磁相互作用场变得相当，竞争导致了与epsilon的矫顽力H-c的降低。对于β的中间值，预测了H-c随ε变化的最大值。不可逆磁化率对相互作用有复杂的依赖关系，特别是在交换和静磁相互作用之间的竞争产生的受挫效应明显的小磁场中。交换和静磁相互作用产生的局域磁序强烈地依赖于交换作用的相对强度。磁序对磁性有很强的影响。还与系统的输运性质建立了联系，这些性质取决于自旋-自旋关联函数。结果表明，交换作用使巨磁电阻与M~(-2)的二次关系发生显著偏离。
A computational model is applied to the study of the hysteresis properties of a system of interacting single domain particles. The model is based on Monte Carlo techniques and takes into account both magnetostatic and exchange interactions. The results presented concentrate on a detailed study of the behavior of Co particles, with the interaction strength varied by variations in the packing density. It is found that the magnetic properties are strongly dependent on the parameter beta=KV/kT, with K the anisotropy constant and V the mean particle volume. For small beta-i.e., close to superparamagnetic systems-the microstructure is dominated by a tendency to flux closure. However, the interactions lead to an increase in the local energy barriers, resulting in an increase in H-c with packing density epsilon. For large beta the anisotropy and magnetostatic interaction fields become comparable and the competition leads to a decrease in the coercivity H-c with epsilon. For intermediate values of beta a maximum in the variation of H-c with epsilon is predicted. The irreversible susceptibility is shown to have a complex dependence on interactions, especially in small fields where frustration effects arising from the competition between exchange and magnetostatic interactions are apparent. Exchange and magnetostatic interactions give rise to local magnetic order which is strongly dependent on the relative strength of the exchange interactions. The magnetic order has a strong bearing on the magnetic properties. A link is also made to the transport properties of the system, which are dependent on a spin-spin correlation function. It is shown that exchange interactions give rise to a significant deviation from the quadratic dependence of the giant magnetoresistance on M-2.