Study Of Super-paramagnetic Property Of Silicon-oil-based Dysprosium Ferrite Magnetic Liquid

Silicon-oil-based magnetic liquid is a kind of functional liquid material. Compared with traditional water-based and kerosene-based magnetic liquid, it has many advantages, such as heat-resisting, good chemical stability, low viscosity and low saturated vapor pressure. In the paper, the preparation of dysprosium ferrite magnetic particles doped by Dy3+ was introduced. The result of investigation about the magnetism of magnetic particles at low temperature, which were modified by surfactant, was reported. Then, the superparamagnetism was proved and the blocking temperature computed by using Langevin function. Finally, the magnetic particles modified by surfactant were dispersed in 2-methyl-silicon-oil by using compulsive measures to prepare silicon-oil-based magnetic liquid and the study results were given out.In the experiment, X-ray diffraction was used to study the crystal structure of dysprosium ferrite magnetic particles. Scanning probe microscopy was used to observe the morphology and size of dysprosium ferrite magnetic particles. Magnetic measure instrument was used to test the magnetism of dysprosium ferrite magnetic particles and to find the bound of blocking temperature. Fourier-trasform infrared spectroscopy was used to analyze the adsorption mode between dysprosium ferrite magnetic particles and surfactant. For the fixed size of dysprosium ferrite magnetic particles, the effect of species and dosage of surfactant, dosage of transition liquid on the magnetism and stability of magnetic liquid was reviewed. Orthogonal experiments were carried out to find out the optimum ratio of magnetic particles, surfactant and transition liquid. Transmission electron microscopy was used to observe dispersion status and size of magnetic particles coated by surfactant in 2-methyl-silicon-oil. Vibrating sample magnetometer was used to test the magnetism of magnetic liquid at room temperature. The result shows that the optimum size of dysprosium ferrite magnetic particles for magnetic liquid is 15.8nm and its crystal structure is cubic spinel. The saturation magnetization of surfactant-modified dysprosium ferrite magnetic particles is 212.5mT at 200.2K. The saturation magnetization increases with the drop of temperature and the correlation between them is close to linearity. A weak hysteresis exists at every low temperature and it becomes more obvious with the drop of temperature. The calculation result of using Langevin function shows that the dysprosium ferrite magnetic particles behave superparamagnetism when their temperature is over 142.8K and the blocking temperature is between 113.9 and 142.8K. The optimum ratio of magnetic particles, lauric acid and transition liquid in magnetic liquid is 1g :0.1g:9mL. The adsorption mode between dysprosium ferrite magnetic particles and surfactant is chemical adsorption. The saturation magnetization of magnetic liquid is 146.4mT at room temperature and it has no hysteresis.