Preparation And Structure Of Hexagonal Barium Ferrite Thin Films And Magnetic Properties

M-type hexa-barium ferrite material has attracted extensive attention for microwave device application and high density perpendicular magnetic recording media due to its large resistivity, high permeability at high frequency, strong uniaixs magnetic anisotropy and stable physical, chemical properties. It is a crucial task for these applications to deposit thick BaM films (thickness >10μm) with high crystalline quality, highly oriented c-axis direction normal to film plane and great out-of-plane squareness of more than 0.9. However, it is hard to obtain such BaM films not only in theroratical research field but also in practical processing community.In this dissertation, it first starts with the c-axis growth process of BaM films on (0001) sapphire substrate and it is systematically studied the experimental relation between the microstructure, surface morphology, magnetic properties of BaM films and their magnetic properties using x-ray diffraction analysis, vibrating sample magnetometer, atom forece microscopy and scanning electron microscopy measurement. Then, an optimal post-annealing processing is found to crystallize the amorphous BaM film, as a crystallized seed layer later. Using a"layer-by-layer"growth mode, it is successfully fabricated crystalline BaM thick films on BaM seed layer buffered sapphire substrate. Meanwhile, it is also systematically studied the fabrication of thick BaM films on TiN, MgO seed layers with highly c-axis orientation and better magnetic properties using this"layer-by-layer"growth mode. Finally, based on the experimental laws derived from the BaM films deposited on sapphire, it is generally discussed the integration of BaM material with GaN epilayer and is successfully fabricated thin BaM films with an excellent performance to some extent. Therefore, it is obtained several conclusions from the above research, as seen below.Firstly, in situ deposited BaM films are amorphous and have low magnetization when the growth temperature is below 750 oC. However, they are highly c-axis oriented, good crystallity and magnetic properties after an optimal post-annealing processing of 1000 oC, 1 h in 1 atm oxygen.Secondly, it is successfully grown 2μm thick BaM films on the crystallized BaM seed layer buffered sapphire with highly c-axis orientation, saturation magnetization of 3500 G, perpendicular squareness of 0.65. When the thickness of BaM films increases to 3.4 micrometer, they have some microcracks in the surface that restrict the improvement of BaM films.Thirdly, thick BaM films with TiN, MgO thin films chosen as seed layer were deposited, which have a saturation magnetization of 4006 G and a perpendicular squareness of 0.7.Lastly, we successfully fabricated BaM thin films on MgO layer buffered GaN substrate with saturation magnetization of 3208 G and perpendicular squareness of 0.7.