Buffer Layer On The Structure And Properties Of Cobalt Ferrite Thin Films

Cobalt ferrite (CoFe₂O₄) thin films can be used as high density magnetic recording media because of its high coercivity, magnetocrystalline anisotropy, excellent chemical stability and mechanical hardness. In this dissertation, effects of underlayers on microstructure and magnetic properties of CoFe₂O₄/Si(100) thin films were investigated, the underlayers were Fe₃O₄ and TbFeCo, respectively.CoFe₂O₄ thin films were deposited on Fe₃O₄ underlayers, which were prepared by DC magnetron sputtering and vacuum annealing, by RF magnetron sputtering. CoFe₂O₄/Fe₃O₄/Si(100) films annealed in atmosphere had cubic spinel structure and without any prefered orientation. It was found that the crystallization temperatures of CoFe₂O₄ films were decreased by Fe₃O₄ underlayers, Fe₃O₄ underlayer promoted the crystallization of the films. The lattice constants of CoFe₂O₄/Fe₃O₄/Si(100) films decreased with increasing annealing temperature, which means that there is large strain in the films, and the films were columnar structure. The magnetic properties of CoFe₂O₄/Fe₃O₄/Si(100) films were isotropy, its perpendicular and parellel coercivities were approximately the same. CoFe₂O₄/Fe₃O₄/Si(100) films annealed at 500℃possessed a perpendicular coercivity of 539.6KAm^-1 and parallel coercivity of 405.2KAm^-1, while had high magnetization and remnant magnetization, its perpendicular remanence ratio was 0.67.CoFe₂O₄ films were prepared on amorphous TbFeCo underlayers which prepared by DC magnetron sputtering. The conventional annealed CoFe₂O₄/TbFeCo/Si(100) films had cubic spinel structure and its texture was effected by the annealing temperature, films annealed at 300℃had (111) prefered orientation while had (400) prefered orientation when annealed at higher temperatures. The lattice constants of CoFe₂O₄/TbFeCo/Si(100) films decreased with increasing annealing temperature, which reveals the films have large strain, the grains of the films were columnar-type. TbFeCo underlayers suppressed Si diffusion while induced Tb duffusing into CoFe₂O₄ films. CoFe₂O₄/TbFeCo/Si(100) films had high perpendicular anisotropy and its magnetic properties were enhanced. Films annealed at 300℃had high coercivity, its perpendicular and parallel coercivities were 616.0KAm^-1 and 360.5 KAm^-1, respectively, but its perpendicular remanence ratio was only 0.49. Films annealed at 800℃had highest coercivity, its perpendicular and parallel coercivities were 832.6 KAm^-1 and 381.6KAm^-1, with perpendicular remanence ratio of 0.73, while films annealed at 900℃had largest perpendicular remanence ratio of 0.90. All films had high magnetization and remant magnetization, and the Curies temperatures of CoFe₂O₄/TbFeCo/Si(100) films were also effected by annealing temperatures.