单域颗粒及组装体的去磁效应对其磁化率的影响
The effect of demagnetization on the susceptibility of single-domain particles and assemblies
AI总结：
研究揭示单域颗粒及组装体的磁化率不受多域材料限制，实验显示其磁化率可高达250以上，为高磁化率复合材料设计提供新思路。
摘要：
根据磁学的经典定律，磁性软物体的形状限制了有效磁化率。例如，球形软磁体无法显示出大于3的有效磁化率。尽管这在宏观多域磁性材料中成立，我们解释了为什么单域磁性纳米颗粒不受这一限制。对于单域颗粒，主轴方向的去磁因子差异相关，并且可以影响磁化率，但不会像多域颗粒那样限制磁化率的上限值。我们通过实验验证了这一结果，针对不同直径（9至150纳米）和不同体积分数（0.1至47体积百分比）的球形纳米颗粒。与我们的预测一致，我们测量到单域颗粒的磁化率远高于3，事实上高达250以上。此外，与现有粒子组装体模型相反，我们发现由非相互作用单域颗粒组成的非磁性基质材料的磁化率与颗粒体积分数成线性关系。这表明，基于纳米颗粒的复合材料可以实现高磁化率（>100），这对在MHz-GHz频率下操作且具有可忽略功率损耗的磁性软材料设计具有相关性。
英文摘要：
According to the classical laws of magnetism, the shape of magnetically soft objects limits the effective susceptibility. For example, spherical soft magnets cannot display an effective susceptibility larger than 3. Although this is true for macroscopic multi-domain magnetic materials, we explain why magnetic nanoparticles in a single-domain state do not suffer from this limitation. For single-domain particles, the differences between demagnetization factors along principal axes are relevant and can influence susceptibility but do not limit the susceptibility to an upper value as in the case for multi-domain particles. We experimentally validated this result on spherical nanoparticles with varying diameter (9 to 150 nm) and varying volume fraction (0.1 to 47 vol%). In agreement with our predictions, we measure single-domain particle susceptibilities largely above 3, in fact up to more than 250. Moreover, contrary to an existing model for assemblies of particles, we find that the susceptibility of materials composed of non-interacting single-domain particles in a non-magnetic matrix scales linearly with the volume fraction of particles. This implies that high susceptibilities (>100) are achievable for nanoparticle-based composites and is relevant for the design of magnetically soft materials that are operational at MHz-GHz frequencies with negligible power losses.
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