Solid State Physics, Department of Engineering Sciences, Uppsala University , 751 21 Uppsala, Sweden.
RISE Acreo , 400 14 Gothenburg, Sweden.
ACS Nano. 2018 Feb 27;12(2):1403-1412. doi: 10.1021/acsnano.7b07745. Epub 2018 Jan 23.
One of the ultimate goals of nanocrystal self-assembly is to transform nanoscale building blocks into a material that displays enhanced properties relative to the sum of its parts. Herein, we demonstrate that 1D needle-shaped assemblies composed of FeO nanocubes display a significant augmentation of the magnetic susceptibility and dissipation as compared to 0D and 2D systems. The performance of the nanocube needles is highlighted by a colossal anisotropy factor defined as the ratio of the parallel to the perpendicular magnetization components. We show that the origin of this effect cannot be ascribed to shape anisotropy in its classical sense; as such, it has no analogy in bulk magnetic materials. The temperature-dependent anisotropy factors of the in- and out-of-phase components of the magnetization have an extremely strong particle size dependence and reach values of 80 and 2500, respectively, for the largest nanocubes in this study. Aided by simulations, we ascribe the anisotropy of the magnetic susceptibility, and its strong particle-size dependence to a synergistic coupling between the dipolar interaction field and a net anisotropy field resulting from a partial texture in the 1D nanocube needles.
纳米晶体自组装的最终目标之一是将纳米级构建块转化为一种材料，使其显示出相对于其各部分总和的增强性能。在此，我们证明了由 FeO 纳米立方体组成的 1D 针状组装体与 0D 和 2D 系统相比，表现出显著增强的磁化率和耗散。纳米立方体针的性能通过定义为平行于垂直磁化分量的比率的巨大各向异性因子来突出。我们表明，这种效应的起源不能归因于其经典意义上的形状各向异性；因此，它在块状磁性材料中没有类似物。磁化的同相和异相分量的温度相关各向异性因子具有极强的粒度依赖性，对于本研究中最大的纳米立方体，分别达到 80 和 2500。通过模拟，我们将磁化率的各向异性及其强烈的粒度依赖性归因于偶极相互作用场与由 1D 纳米立方体针的部分织构引起的净各向异性场之间的协同耦合。
