Structure And Magnetic Properrtties Of Hexagonal Ferrite SrFe_12-xIn_xO₁₉ And Half Heusler Ir_0.9Mn_1-xSn_1.1+x

In this thesis,we have studied the crystal structure,optical properties and magnetic properties of hexagonal ferrite SrFe_12-xIn_xO₁₉,as well as the magnetic and carrier transport of the Half Heusler alloy Ir_0.9Mn_1-xSn_1.1+x.SrFe_12-xIn_xO₁₉?x=0,0.1,0.2,0.3,0.4,0.5,1 and 2?crystallize in the hexagonal structure.From the XRD refinement and the FT-IR spectra,it is deduced that the In³⁺ions preferentially occupy the tetragonal 4f₁ site.The band gap of SrFe_12-xIn_xO₁₉increases with the increasing In³⁺content from 1.75 eV for x=0 to 1.87 eV for x=1,but that of x=2 decreases to 1.79 eV.The Curie temperature of SrFe_12-xIn_xO₁₉ decreases linearly with the doped nonmagnetic In³⁺from 740 K for x=0,and 610 K for x=1,and it decreases at a much lower rate to 592 K for x=2.The XPS spectra,the FT-IR spectra,and the band gap lead to the same conclusion that In2 has oxygen voids,which are in favor of the exchange interaction by increasing the Fe²⁺content.The saturation magnetization at 300 K increases with the In³⁺content up to the highest value of 73.87emu/g at 0.5,and decreases with further doped In³⁺.The coercive field keeps almost the same for x?0.2,but decreases with the further increasing In³⁺content.The nonstoichiometric Ir_0.9Mn_1-xSn_1.1+x?x=0.1,0.05 and-0.05?are crystallized in half Heusler alloys.The magnetic transition is observed at 77 K for x=1.05,and it decreases with the decreasing Mn content.It is proved to be a ferromagnetic transition with nonlinear magnetic moment alignment,as the magnetization is not saturated at 70kOe.The different magnetic behavior than a typical FM is due to the Ir ions with strong SOC.The different hysteresis loops reflect that the ionic distribution is not completely homogeneous.The high coercivity observed in the cubic compound is due to the strong single ion anisotropy of the Ir ions.A metallic-semiconducting transition at 130 K is observed in Ir_0.9Mn_1.05Sn_1.05.A negative magnetoresistance is observed at 2 K and 14 T with the value as-2.6%.