Terahertz Time Domain Spectroscopy Of Magnetically Ordered Materials

Terahertz（THz）radiations，also known as far-infrared waves or submillimeterelectromagnetic waves，are in the range between microwave and infrared. With thedevelopment of terahertz technology, terahertz science in wereless communications,imaging, and security is gradually showing a very broad application prospects. Thedevelopment of terahertz（THz）technology provides an effective tool for investigatingthe interaction of light and matter on critical timescales. Super fast dynamics researchof magneticaly ordered materials has become the hot destination of material physics,which promote the development of spintronics. This paper based on THZ time domainspectroscopy, we choose three types of magnetically ordered materials, perovskite,magnetic lead stone and wurtzite as the research object in this thesis. The main workin the thesis includes:1、By employing the magnetic field component of THz pulse, we investigated thespin wave excitation and dispersion in canted antiferromagnetic materials, such asYFeO3and DyFeO3crystals et al. With resonant excitation on the magnetic resonancein the canted antiferromagnetic crystal, the quasi-ferromagentic mode (F-mode) andquasi-antiferromagnetic mode (AF-mode) can be excited effectively and controlledcohererntly with THz pulses.2、THz-TDS was used to study the absorption coefficient and refractive index ofbarium ferrite and Al doped barium ferrite in magnetically ordered materials. Theresults show that，for a barium ferrite, the annealing temperature has significantinfluence on the absorption coefficient and the refractive index of barium ferrite.Within0-1.2THz wave band, the absorption coefficient increases with frequency fordifferent annealing temperature of barium ferrite sample, the refractive indexdecreases with the frequency with different annealing temperature of barium ferrite,and the refractive index of barium ferrite sample is larger with the increase ofannealing temperature.For Al-doped barium ferrite, the absorption coefficients for these samples annealing at1000℃and1100℃temperature shows a strong absorption at0.67THz.Near the absorption peak (0.67THz), the refractive index of samples decreasesslightly with the increase of the frequency, which presents the anomalous dispersioncharacteristics. Our results reveal that the lattice structure of the barium ferrite can bemodified by dopant, as a result, the absorption coefficient and the refractive index ofbarium ferrite are reduced with Al doping.3、The absorption coefficient and refractive index of ZnO single crystal，ZnO andMg-doped ZnO nanostructure were studied by THz-TDS. The results show that Mgdoped leads to the increase of the absorption coefficient, while decrease the refractiveindex of the compound ZnO. In0.2-2.0THz frequency domain, THz dielectricproperties of ZnO nanostructure and Mg-doped ZnO nanostructure exhibit similarbehaviors with that of the ZnO single crystal, which are found to be associated withthe transverse optical phonon mode.