Study On The Magnetic Properties Of MgFe₂O₄ Nanoparticles Prepared By Solid State Synthesis At Low Heating Temperatures

Nano-Ferrite materials have very wide application foreground in the areas of Physics, Biology and Iatrology etc. For instance, we can smear macromolecule organic material on magnetic Ferrite nanoparticles and combine them with drugs that can cure certain diseases. We can inject them into body and concentrate the nanoparticles to the place of focus to cure the diseases under the guidance of external magnetic field. This technique has currently passed the clinic experiments. In addition, we could also concentrate the nanoparticles to the place of focus straightway under the guidance of external magnetic field without combining them with drugs. Because the heat which is generated from magnetic materials under alternating magnetic field could alao cure some cancers. Study results given by K. Konishi improve that MgFe₂O₄ has sufficient heating ability for thermal coagulation therapy against cancer. Thus, to produce MgFe₂O₄ nanoparticles and to study their Macro-magnetism and Micro- magnetism have very great value to the basic application research.In this thesis, we introduced a new method of "solid state reaction at low temperature" to prepare MgFe₂O₄ nanoparticles, it only needs very simple equipments and it is very easy to operate. The structure and grain size of the samples have been obtained by means of X-ray Diffraction Instrument. Then the macro-magnetism of the nanoparticles has been studied using Vibrating Sample Magnetometer (VSM). The micro-magnetism of the nanoparticles has been investigated by Mossbauer Spectroscopy. At last the super-paramagnetism in MgFe₂O₄ nanoparticles is studied using Mossbauer Spectroscopy in the temperature range of 77 K-300 K. The main conclusions are as follows:(1) MgFe2O4 nanoparticles have been prepared by a new method of solid state synthesis at low temperatures. The pattern of XRD shows the lattice constants of nanosized MgFe₂O₄ are larger than that of bulk material.(2) The room-temperature results of VSM indicate that the cation occupancy varies with particle size.(3) Mossbauer spectra and the room-temperature results of VSM of MgFe2C>4 nanoparticles indicate that the transition size of super-paramagnetic at room temperature is about 25 nm, and the single domain critical size of MgFe2O4 is about 28 nm.(4) Magnetic thermal-gravity analysis was employed to measure the Curie temperature Tc of the nanoparticles. It shows that Tc varies in the range of 317- 374 °C, while the Tc value for bulk NiFe2O4 is 440 °C. It is interesting that, the variation of the Curie temperatures for nanoparticles and the variation of lattice constant for nanoparticles have inverse relationship.(5)The effects of thermal disturbance and particle size on the microscopicmagnetic properties were investigated by Mossbauer spectroscopy. At a certaintemperature, the hyperfine field decreases with the decrease in particle size. To a certain sample, the hyperfine field rises with the decrease in temperature.