Development of hightly oriented and low noise barium ferrite thin film media for high density magnetic recording

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Hexagonal barium ferrite (BaM : BaFe_<12>O_<19>) thin films are promising high density magnetic recording media, because they have not only excellent magnetic properties (large magnetic anisotropy energy) but also good mechanical and chemical stability. And because BaM is an oxide, the exchange interaction between the crystallites is easily reduced, which is necessary for a low-noise recording media. In this research, we attempted to obtain the BaM thin film with excellent c-axis orientation at a low substrate temperature by alternate periodic deposition of an S layr (spinel Fe_3O_4) layr) and an R (BaO・3Fe_2O_3) layr. Control of crystallite size in the BaM film was also attempted.(1) Control of crystallite size in the filmThe crystallite size in the BaM film decreased monotonically with decreasing film thickness, reaching a value below 30 nm in films 30 nm thick. Further decreases in film thickness led to a degradation of the crystallinity of the film, causing the saturation magnetiza … More tion and coercive force of the film to decrease significantly. A ZnO underlayr promoted the growth of c-axis-oriented hexagonal BaM crystallites in the film, but was not effective in reducing the crystallite size of the film. Furthermore, diffusion of Zn atoms from the underlayr to BaM film caused a decrease in the coercive force and saturation magnetization of the film. Growth of BaM crystallites in films deposited on a SiO_2/Si substrate was significantly suppressed when the films were deposited on a thin initial layr deposited on a SiO_2/Si substrate was significantly suppressed when the films were deposited on a thin initial layr deposited beforehand under a substrate bias of-50V.(2) Deposition of BaM film by alternate layr deposition methodDeposition of c-axis perpendicularly oriented barium ferrite (BaM : BaFe_<12>O_<19> thin films was attempted by means of an alternate periodic deposition of S (spinel Fe_3O_4 and R (BaO・3Fe_2O_3) layrs. The period of the layrs was fixed at 1.15 nm, which corresponds to the period of hexagonal barium ferrite crystals in the c-axis direction. The films deposited at temperatures above 540ﾟC had a hexagonal crystal structure and showed excellent c-axis orientation, but this deposition method did not results in a marked reduction of substrate temperature needed for the deposition of a BaM film with hexagonal crystal structure. The films deposited at 630ﾟC had a clear terraced surface due to the growth of disk shaped hexagonal crystallites. The saturation magnetization of the film was about 220 emu/cc and the coercive force of the films was about 2.2kOe. Less