Zhang Yajing, Or Siu Wing, Zhang Zhidong
J Nanosci Nanotechnol. 2014 Jun;14(6):4664-9. doi: 10.1166/jnn.2014.8645.
Magnetite (Fe3O4) hollow nanospheres with an average diameter of 300 nm and an average shell thickness of 40 nm were synthesized by a surfactant-free solvothermal reduction method, and their structure and electromagnetic (EM) properties were investigated. The Fe3O4 hollow nanospheres showed single-crystalline features along the [111] crystal growth direction and a ferrimagnetic behavior at room temperature. The Fe3O4 hollow nanosphere/paraffin composites exhibited a flatter response in the real complex relative permittivity (epsilon') and a lower value of -0.5 in the imaginary complex relative permittivity (epsilon") in comparison with other Fe3O4-based nanomaterials because of the enhanced electrical resistivity. Their imaginary complex relative permeability (mu") displayed a resonance peak at -4 GHz and a negative value up to -0.03 in the 17.2-18 GHz range due to the dissipation of EM energy in the cavity of the hollow nanospheres. Their reflection loss (RL) exceeded -10 dB from 3.1 to 10.1 GHz at a thickness of 2.6-5 mm and attended an optimal value of -43.5 dB at 4 GHz at 5 mm thickness as a result of an effective complementation between the dielectric and magnetic losses.
采用无表面活性剂的溶剂热还原法合成了平均直径为300nm、平均壳层厚度为40nm的磁铁矿（Fe3O4）空心纳米球，并对其结构和电磁（EM）性能进行了研究。Fe3O4空心纳米球沿[111]晶体生长方向呈现单晶特征，在室温下表现出亚铁磁性行为。与其他Fe3O4基纳米材料相比，Fe3O4空心纳米球/石蜡复合材料在实部复相对介电常数（ε'）方面表现出更平缓的响应，在虚部复相对介电常数（ε"）方面的值较低，为-0.5，这是由于电阻率增强所致。由于空心纳米球腔内电磁能量的耗散，其虚部复相对磁导率（μ"）在-4GHz处出现共振峰，在17.2-18GHz范围内高达-0.03的负值。由于介电损耗和磁损耗之间的有效互补，其反射损耗（RL）在厚度为2.6-5mm时从3.1到10.1GHz超过-10dB，在5mm厚度时于4GHz处达到-43.5dB的最佳值。
