The Meissner Effect Of Monodisperse In Nanoparticles And Magnetic Properties Of Fe₃Se₄Nanoparticles

The properties of nanomaterials are different from the bulk materials, both in terms of the thebasic characteristics of nanomaterials, and in terms of the unique nature of the material itself.Synthesis and properties of nanomaterials has been the hotspot of the materials science today.Based on synthesis, phase morphology analysis and characterization of physical properties, themain work of the thesis is to study some Superconductivity and magnetic evolution law of thenanomaterials system. The main content is listed as follow:1. Monodisperse In nanoparticles were successfully synthesised through a hot-injectionmethod in polyol solution. The samples were characterized with XRD, SEM, TEM and PPMS.The results show that the superconducting critical temperature of indium nanoparticles is directlyrelated to the particle size. The appearance of this regime is closely related to size effect and thediscrete nature of the electronic levels; The M-H curves under different magnetic fields show thatthe critical magnetic field of the nanoparticles is higher than that of the bulk material. We concludethat the effect is originated from the field penetrating into the particle; The result of M-H curveshows that superconductivity and ferromagnetism coexist at low temperature, as a result of theexistence of the surface spin; For comparation, we further synthesised In nanorods with Layeredmicro-nano structure and the result of ZFC curve shows that the critical temperature of the sampleis4%lower than that of the bulk form.2. Fe₃Se₄nanoparticles with size of28nm were successfully synthesised through a organic-solution-phase chemical method. Magnetic hysteresis loops were measured for ferrimagnetic ironchalcogenide Fe₃Se₄nanoparticles in the whole temperature range below the Curie temperature TC（315K）. The coercivity of the material is huge, reaching about40kOe at10K. The magneticanisotropy constant K is determined from the magnetic hysteresis loop using the law of approachto saturation. The deduced anisotropy constant at10K is5.22×10⁶erg/cm³, which is one order ofmagnitude larger than that of Fe₃O₄; We also demonstrate that the experimental magnetichysteresis loop is in good agreement with the theoretical curve calculated by Stoner and Wohlfarth;Moreover, we show that K is proportional to the cube of the saturation magnetization Ms, whichconfirms earlier theoretical models for uniaxial magnets.