Study Of Tunable Magneto-optical Properties Of Cobalt Doped Ce_xHf_1-xO₂

Magneto-optical oxide materials such as yttrium iron garnets(Y3Fe5O12,YIG)are widely used in nonreciprocal photonic devices due to their room temperature ferromagnetism,and strong magneto-optical properties.The electric dipole transition energies of most magneto-optical oxides are located in the ultraviolet to the visible wavelength range,making the magneto-optical spectra of these materials non-tunable,so the best performance of these materials only achievable in the near infrared and the applied wavelength range of these materials is limited.On the other hand,dilute magnetic insulators based on transition metal ion doped insulating oxides is an important room temperature ferromagnetic and magneto-optical material,so far,the relationship between magneto-optical properties and bandgap of this kind of material remains unclear,the systematic work of preparation and characterization is not yet.If the tunable magnetooptical properties of magneto-optical films based on transition metal ion doped insulating oxides can be developed,it will extend the applied wavelength range of the existing magneto-optical materials and provide new materials for nonreciprocal photonic devices in the ultraviolet to the visible wavelength range.To address the above problem,in this paper,we present a novel magneto-optical material based on Cobalt doped CexHf1-x O2,which shows room temperature ferromagnetic properties,tunable magneto-optical spectrum.It shows high magnetooptical figure of merit(FOM)in the visible wavelength range by tuning the bandgap.In the second chapter,we introduce the experiment and calculation methods.The experiment methods contain the preparation of targets,the preparation process and the characterization methods.The calculation method includes the first principle calculation based on the density functional theory,which is mainly used to study the structure,magnetic and magneto-optical properties of the materials.In the third chapter,we introduce the experiment results of Cobalt doped CexHf1-xO2 thin films.We deposit the CexHf0.95-xCo0.05O2-? films on quartz substrates by pulse laser deposition(PLD).By setting the doped atomic content of Cobalt as 5 at.%,and changing the ratio of Ce and Hf,we mainly study its influence on the bandgap,magnetic and magneto-optical properties of the films.We systematically characterize the crystal structure,magnetic,optical and magneto-optical properties of the films by X-ray diffraction,vibrating sample magnetometer,ultraviolet and visible spectrophotometer and Faraday rotation.All the films show good crystallinity and room temperature ferromagnetic.The optical bandgap of the films increase from 3.5 eV to 5.5 eV as Ce content decrease from 0.95 to 0,and the magneto-optical spectra blue-shifts as the optical band gap increases.Thus we achieved a novel magneto-optical material with tunable magneto-optical properties.Lastly,in the fourth chapter,we introduce the mechanism of the origin of the magnetic and magneto-optical properties of Cobalt doped CexHf1-xO2 system.We calculate the crystal structure,magnetic,optical properties of Cobalt doped CexHf1-xO2 by first principle calculation in two cases,one is the vacancy oxygen is far away from Cobalt,another is the vacancy oxygen is near Cobalt.We get the conclusion that the Co-O acceptor-donor defect complex induced ferromagnetism,and the electric dipole transition of the defect bands induced sub-band gap,tunable magneto-optical properties.The novel magneto-optical Cex Hf0.95-x Co0.05O2-? thin films developed in this thesis,which show room temperature ferromagnetic properties,tunable magneto-optical spectrum,are promising candidates for nonreciprocal photonic devices in the ultraviolet to the visible wavelength range.