Estimation of Magnetic Anisotropy of Individual Magnetite Nanoparticles for Magnetic Hyperthermia
Estimation of Magnetic Anisotropy of Individual Magnetite Nanoparticles for Magnetic Hyperthermia
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DOI：
10.1021/acsnano.0c02521
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发表时间：
2020-07-28
期刊：
影响因子：
17.1
通讯作者：
Balachandran, Jeyadevan
中科院分区：
文献类型：
--
作者：
Mamiya, Hiroaki;Fukumoto, Hiroya;Balachandran, Jeyadevan
制备了理想的无相互作用磁铁矿纳米颗粒，并测量了它们的磁性能，以阐明纳米级单个磁铁矿纳米颗粒磁各向异性的真实性质，并分析形状、表面和晶体各向异性的贡献。采用溶液技术合成了平均尺寸为 7.6 至 23.4 nm 的球形（17.7 nm）、立方体（10.6 nm）和八面体形状的磁铁矿纳米颗粒。然后，将这些纳米颗粒以适当的壳厚度涂覆二氧化硅，制备无磁相互作用的样品，并通过一阶反转曲线图证实了它们的非相互作用性质。对于这些隔离良好的纳米粒子，磁滞回线的剩余磁化强度仅等于饱和磁化强度的一半。该结果清楚地表明单轴磁各向异性在每个纳米粒子中占主导地位。为了阐明单轴磁各向异性的细节，基于不同施加场下等温剩磁的热衰减曲线构建了阻塞温度转换场分布图的分析。获得的有效磁各向异性常数K-eff分布在10-20 kJ/m(3)左右，并且尺寸依赖性不显着。这个结果似乎与 K-eff 与表面磁各向异性预测的尺寸的反比例关系不一致。理论计算表明，晶体磁各向异性对磁铁矿纳米颗粒在较低温度下的磁性能起着重要作用。然而，应该注意的是，对于不同的形状，K-eff 似乎略有不同。上述研究表明，需要控制尺寸、形状和颗粒间相互作用，以严格讨论单个磁铁矿纳米颗粒的磁各向异性的这种微妙差异，以设计用于磁热疗的热种子。
Ideal interaction-free magnetite nanoparticles were prepared, and their magnetic properties were measured to clarify the true nature of magnetic anisotropy of individual magnetite nanoparticles at the nanoscale and to analyze the shape, surface, and crystalline anisotropy contributions. Spherical (17.7 nm), cubic (10.6 nm), and octahedral-shaped magnetite nanoparticles with average sizes ranging from 7.6 to 23.4 nm were synthesized using solution techniques. Then, these nanoparticles were coated with silica at appropriate shell thicknesses to prepare magnetic interaction-free samples, and their noninteractive nature was confirmed through first-order reversal curve diagrams. For these well-isolated nanoparticles, remanent magnetizations of the hysteresis loops are just equal to a half of the saturation magnetization. This result clearly indicates that uniaxial magnetic anisotropy is predominant in each nanoparticle. In order to clarify the details of the uniaxial magnetic anisotropy, the analysis of blocking temperature-switching field distribution diagrams is constructed based on thermal decay curves of isothermal remanent magnetization at various applied fields. The obtained effective magnetic anisotropy constant K-eff is distributed around 10-20 kJ/m(3) and has insignificant size dependence. This result seems inconsistent with the inverse proportion relation of K-eff with size predicted for surface magnetic anisotropy. The theoretical calculation suggested that the crystalline magnetic anisotropy plays a major role in magnetic properties of the magnetite nanoparticles at lower temperatures. However, it should be noted that K-eff seems slightly different for the different shapes. The above study indicates that control size, shape, and interparticle interactions is required to strictly discuss such delicate differences of magnetic anisotropy of individual magnetite nanoparticles for the design of thermal seeds for magnetic hyperthermia.