Quantifying exchange coupling in segregated granular materials
Quantifying exchange coupling in segregated granular materials
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DOI：
10.1088/0022-3727/46/47/475002
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发表时间：
2013-11
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影响因子：
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通讯作者：
Christopher Morrison;L. Saharan;Yoshihiro Ikeda;K. Takano;G. Hrkac;Thomas Thomson
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作者：
Christopher Morrison;L. Saharan;Yoshihiro Ikeda;K. Takano;G. Hrkac;Thomas Thomson
磁性颗粒的体积及其各向异性决定了热激活反转的概率。因此，对于中值体积接近超顺磁性极限的颗粒体积分布，将存在在典型磁性测量的时间尺度上（10 s）为超顺磁性的颗粒子集，或者由于来自周围颗粒的静磁场而相反。我们使用这种效应来探测隔离颗粒材料中的交换耦合，使用CoCrPt-SiOx颗粒记录介质作为模型系统。当薄膜厚度减小到10 nm以下时，由于热激活和静磁反转，这些薄膜的剩余磁化强度降低。改变薄膜厚度和温度使我们能够热选择有助于测量的颗粒群。交换耦合的特点是角度依赖的rebellivity，我们关联的对称性从Stoner-Wohlfarth模型对Kondorsky模型作为衡量的不一致性的逆转的破坏。结合这些模型允许的估计是由交换耦合的晶粒的体积分数，我们发现，对于良好的隔离CoCrPt-SiOx介质，大约8%的磁体积进行一定程度的交换耦合。
The volume of a magnetic grain, together with its anisotropy, determines the probability of thermally activated reversal. Thus for grain volume distributions where the median volume is close to the superparamagnetic limit there will be a sub-set of grains which are either superparamagnetic on the time scale of a typical magnetic measurement (10 s), or the reverse due to magnetostatic fields from surrounding grains. We use this effect to probe exchange coupling in segregated granular materials, using CoCrPt–SiOx granular recording media as model systems. As the film thickness is reduced below 10 nm, the remanent magnetization of these films decreases, due to thermal activation and magnetostatic reversal. Varying film thickness and temperature allows us to thermally select a population of grains that contribute to the measurement. Exchange coupling is characterized by the angle dependence of remanent coercivity where we associate a breaking of symmetry from the Stoner–Wohlfarth model towards the Kondorsky model as a measure of the incoherency of reversal. Combining these models allows an estimate to be made of the volume fraction of grains that are exchange coupled and we find that, for well segregated CoCrPt–SiOx media, approximately 8% of the magnetic volume undergoes some degree of exchange coupling.