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首页> 美国卫生研究院文献>International Journal of Molecular Sciences >Demagnetization Treatment of Remanent Composite Microspheres Studied by Alternating Current Susceptibility Measurements
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Demagnetization Treatment of Remanent Composite Microspheres Studied by Alternating Current Susceptibility Measurements

机译：交流磁化率测量研究剩余复合微球的消磁处理

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摘要

The magnetic remanence of silica microspheres with a low concentration of embedded cobalt ferrite nanoparticles is studied after demagnetization and remagnetization treatments. When the microspheres are dispersed in a liquid, alternating current (AC) magnetic susceptibility spectra reveal a constant characteristic frequency, corresponding to the rotational diffusion of the microparticles; this depends only on particle size and liquid viscosity, making the particles suitable as a rheological probe and indicating that interactions between the microspheres are weak. On the macroscopic scale, a sample with the dry microparticles is magnetically remanent after treatment in a saturating field, and after a demagnetization treatment, the remanence goes down to zero. The AC susceptibility of a liquid dispersion, however, characterizes the remanence on the scale of the individual microparticles, which does not become zero after demagnetization. The reason is that an individual microparticle contains only a relatively small number of magnetic units, so that even if they can be reoriented magnetically at random, the average vector sum of the nanoparticle dipoles is not negligible on the scale of the microparticle. In contrast, on the macroscopic scale, the demagnetization procedure randomizes the orientations of a macroscopic number of magnetic units, resulting in a remanent magnetization that is negligible compared to the saturation magnetization of the entire sample.
机译：经过消磁和复磁处理后，研究了具有低浓度嵌入钴铁氧体纳米粒子的二氧化硅微球的剩磁。当微球分散在液体中时，交流磁化率谱显示出恒定的特征频率，对应于微粒的旋转扩散。这仅取决于粒度和液体粘度，这使得该颗粒适合用作流变探针，并表明微球之间的相互作用较弱。在宏观尺度上，具有干燥微粒的样品在饱和磁场中处理后会剩磁，而在去磁处理后，剩磁降为零。然而，液体分散体的AC磁化率表征了单个微粒的剩余磁化强度，该磁化强度在退磁后不会变为零。原因是单个微粒仅包含相对较少数量的磁性单元，因此，即使它们可以被随机地磁取向，纳米微粒偶极子的平均矢量和在微粒尺度上也是不可忽略的。相反，在宏观尺度上，退磁过程使宏观数量的磁性单元的方向随机化，从而导致剩余磁化强度与整个样本的饱和磁化强度相比可忽略不计。

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