Fock Jeppe, Jonasson Christian, Johansson Christer, Hansen Mikkel Fougt
Department of Micro- and Nanotechnology, DTU Nanotech, Technical University of Denmark, Bldg. 345B, DK-2800 Kongens Lyngby, Denmark.
Acreo Swedish ICT AB, Box 53071, SE-400 14 Gothenburg, Sweden.
Phys Chem Chem Phys. 2017 Mar 29;19(13):8802-8814. doi: 10.1039/c6cp08749c.
The remanent magnetic moment and the hydrodynamic size are important parameters for the synthesis and applications of magnetic nanoparticles (MNPs). We present the theoretical basis for the determination of the remanent magnetic moment and the hydrodynamic size of MNPs with a narrow size distribution using optomagnetic measurements. In these, the 2nd harmonic variation of the intensity of light transmitted through an MNP suspension is measured as a function of an applied axial oscillating magnetic field. We first show how the measurements of the optomagnetic signal magnitude at a low frequency vs. magnetic field amplitude can be used to determine the MNP moment. Subsequently, we use linear response theory to describe the dynamic non-equilibrium response of the MNP suspension at low magnetic field amplitudes and derive a link between optomagnetic measurements and magnetic AC susceptibility measurements. We demonstrate the presented methodology on two samples of commercially available multi-core MNPs. The results compare well with those obtained by dynamic light scattering, AC susceptibility and vibrating sample magnetometry measurements on the same samples when the different weighting of the particle size in the techniques is taken into account. The optomagnetic technique is simple, fast and does not require prior knowledge of the concentration of MNPs and it thus has the potential to be used as a routine tool for quality control of MNPs.
剩余磁矩和流体动力学尺寸是磁性纳米颗粒（MNPs）合成与应用的重要参数。我们给出了使用光磁测量来确定尺寸分布窄的MNPs的剩余磁矩和流体动力学尺寸的理论基础。在这些测量中，测量透过MNP悬浮液的光强的二次谐波变化作为施加的轴向振荡磁场的函数。我们首先展示如何利用低频下光磁信号幅度相对于磁场幅度的测量来确定MNP磁矩。随后，我们使用线性响应理论来描述低磁场幅度下MNP悬浮液的动态非平衡响应，并推导光磁测量与磁交流磁化率测量之间的联系。我们在两种市售多核MNPs样品上展示了所提出的方法。当考虑到不同技术中粒度的不同权重时，结果与通过动态光散射、交流磁化率和振动样品磁强计对相同样品进行测量所得到的结果吻合良好。光磁技术简单、快速，并且不需要预先知道MNPs的浓度，因此有潜力用作MNPs质量控制的常规工具。
