Bimodal distribution of the magnetic dipole moment in nanoparticles with a monomodal distribution of the physical size
Bimodal distribution of the magnetic dipole moment in nanoparticles with a monomodal distribution of the physical size
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DOI：
10.1016/j.jmmm.2014.09.058
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发表时间：
2015-04
影响因子：
2.7
通讯作者：
J. Rijssel;B. Kuipers;B. Erné
中科院分区：
文献类型：
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作者：
J. Rijssel;B. Kuipers;B. Erné
磁性纳米粒子的高频应用，如热疗和磁性粒子成像，对纳米粒子的尺寸和偶极矩很敏感。通常，假设具有对数正态分布的物理尺寸的磁性纳米颗粒也具有对数正态分布的磁偶极矩。在这里，我们测试这种假设为不同类型的超顺磁性氧化铁纳米粒子在5-20 nm的范围内，通过多峰拟合的磁化曲线，使用MINORIM反演方法。研究的颗粒，而在稀释的胶体分散在液体中，从而防止滞后和减少磁各向异性的磁化曲线的解释的影响。对于两种不同类型的结晶良好的颗粒，磁分布确实是对数正态的，正如从物理尺寸分布所预期的那样。然而，其他两种类型的颗粒，与孪生缺陷或不均匀的氧化物相，被发现具有双峰磁性分布。我们的定性解释是，相对较低的磁场足以开始排列液体中的颗粒的基础上，他们的净偶极矩，而更高的领域需要调整较小的域或较少的磁性相内的颗粒。
High-frequency applications of magnetic nanoparticles, such as therapeutic hyperthermia and magnetic particle imaging, are sensitive to nanoparticle size and dipole moment. Usually, it is assumed that magnetic nanoparticles with a log-normal distribution of the physical size also have a log-normal distribution of the magnetic dipole moment. Here, we test this assumption for different types of superparamagnetic iron oxide nanoparticles in the 5–20 nm range, by multimodal fitting of magnetization curves using the MINORIM inversion method. The particles are studied while in dilute colloidal dispersion in a liquid, thereby preventing hysteresis and diminishing the effects of magnetic anisotropy on the interpretation of the magnetization curves. For two different types of well crystallized particles, the magnetic distribution is indeed log-normal, as expected from the physical size distribution. However, two other types of particles, with twinning defects or inhomogeneous oxide phases, are found to have a bimodal magnetic distribution. Our qualitative explanation is that relatively low fields are sufficient to begin aligning the particles in the liquid on the basis of their net dipole moment, whereas higher fields are required to align the smaller domains or less magnetic phases inside the particles.