Magnetic interactions and reversal behaviour of Nd2Fe14B particles diluted in a Nd matrix
Magnetic interactions and reversal behaviour of Nd2Fe14B particles diluted in a Nd matrix
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DOI：
10.1103/physrevb.66.184418
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发表时间：
2002-11
影响因子：
3.7
通讯作者：
D. Crew;Erol Girt;D. Suess;T. Schrefl;K. Krishnan;G. Thomas;M. Guilot
中科院分区：
文献类型：
--
作者：
D. Crew;Erol Girt;D. Suess;T. Schrefl;K. Krishnan;G. Thomas;M. Guilot
用可逆磁化强度测量、微磁模拟、矫顽力与温度的关系和磁粘度测量，阐明了含Nd2Fe14B颗粒的磁反转机制。随着Nd2Fe1.4B相稀释度的增加，样品的矫顽力显著增加。矫顽力的增加伴随着反转机制的改变。在稀释度最低的样品中，由晶间相互作用控制的多个颗粒的畴壁运动是活跃的。在最稀薄的样品中，单个颗粒的不均匀反转占主导地位，反转发生在一个接一个的颗粒上，类似于孤立的斯通纳-沃尔法斯颗粒的行为。当计入磁化反转的热激活效应时，最稀薄样品的矫顽力与孤立颗粒的微磁模拟结果吻合较好。尽管最稀薄的样品具有单颗粒翻转机制，但未观察到矫顽力与堆积分数的线性关系。这归因于样品中颗粒的聚集和颗粒形状随成分的变化。在所有样品中，无论稀释程度如何，热退磁后的初始磁状态都是相当大比例的颗粒处于多磁区状态。然而，对形状类似于最稀薄样品中的孤立粒子的微磁模拟表明，单畴状态是最低的能量状态。结果表明，热退磁可以使系统保持局部亚稳态，而不是全局能量极小值。微磁计算表明，在热退磁过程中，颗粒中可能会出现一个或多个磁畴壁，而静磁效应在零场下为磁化壁的去除提供了一个重要的零场能垒。
Reversible magnetization measurements, micromagnetic modeling, the temperature dependence of coercivity, and magnetic viscosity measurements have been used to clarify the magnetic reversal mechanism of Nd 2 Fe 1 4 B particles contained in a Nd matrix. The coercivity was observed to increase markedly as the dilution of the Nd 2 Fe 1 4 B phase was increased. The increase in coercivity was accompanied by a change in the reversal mechanism. In the least dilute samples, domain wall motion involving several grains governed by intergrain interactions was active. In the most dilute samples nonuniform reversal of individual grains was dominant, reversal occurring particle by particle and resembling the behavior of isolated Stoner-Wohlfarth particles. The value of the coercivity in the most dilute sample was in excellent agreement with micromagnetic modeling results for isolated particles when the effect of thermal activation of magnetization reversal was accounted for. Despite the single particle reversal mechanism of the most dilute samples, a linear dependence of coercivity on packing fraction was not observed. This is attributed to a clustering of the grains in the samples and changes in grain shape with composition. In all samples, regardless of dilution, the initial magnetic state after thermal demagnetization was found to be one in which a substantial proportion of grains were in a multidomain state. However, micromagnetic simulations for isolated particles of similar shape to those in the most dilute sample showed that the single domain state is the lowest energy state. It is concluded that thermal demagnetization can result in the system remaining in a local metastable state and not the global energy minimum. Micromagnetic calculations showed that one or more domain walls can arise in a grain during thermal demagnetization and that magnetostatic effects provide a significant energy barrier in zero field to the removal of a domain wall once it is formed.