| Among several ferrite materials, barium ferrite has received much attention due to its high saturation magnetization, large coercivity, large uniaxial anisotropy, excellent chemical stability and high resistivity, and its film is suitable for fabrication of high density magnetic recording media as well as high frenquency microwave devices. The common requirements for the BaM film are following: firstly, sufficient content of BaM phase is needed to reach high Ms; secondly, the BaM grains should keep the magnetically easy c-axis normal to the film plane to obtain large uniaxial anisotropy and Hc, which is vitally important to the vertical recording; thirdly, the grain size of barium ferrite should be small to reduce the media noise and attain higher recording density. Fabrication of BaM films was mostly achieved via sputtering, pulsed laser deposition (PLD) and Sol-Gel processing. It is well known that the phase formation and magnetic properties of BaM films are greatly dependent on the precursory sols, especially on the Fe/Ba ratio. Usually, a certain barium surplus is used to form the ideal hexaferrite phase. Therefore, one question rises whether the higher content of single BaM phase can be formed in higher Fe/Ba ratio (more than 6) films and results in good magnetic. In this paper, we will discuss the properties of films prepared by Sol-Gel technology, and study the Fe/Ba ratio of the sols and the amount of citric added to the precursory sols, annealing temperatures will also be discussed.The results showed the BaM phase can be formed and crystallized into c-axis textured grains even when the Fe/Ba ratio of the precursor varied from 6.5 to 9.5. However, the behavior of the saturation magnetization (Ms) and intrinsic coercivity (Hc) depended strongly on the Fe/Ba ratio and annealing temperature (Ta) varied from 700900℃. The Ms and Hc values deceased with an increase of Fe/Ba ratio, for instance, they were about 290 emu/cm3 and 4200 Oe for the Fe/Ba = 6.5 film but only 116 emu/cm3 and 2300 Oe for the Fe/Ba = 9.5 film. With the increase of Fe/Ba ratio,α-Fe2O3 phase emerged and reduced the effective volume of barium ferrite, and resulted in the decrease of saturation magnetization and coercivity of the films. The Ms and Hc values of the Fe/Ba = 6.5 film increased monotonously with increasing Ta, were about 120 emu/cm3 and 2500 Oe at Ta = 800℃, and reached to 345 emu/cm3 and 4600 Oe at Ta = 900℃. Increasing annealing temperature for the Fe/Ba = 6.5 film showed that more acicular BaM phase formed in the films accompanying with the improvement of saturation magnetization and coercivity.In the process of preparation c-axis BaM film, the citric as catalyzer and chelate to the sols is another important issue to the properties of BaM films. The results showed that the amount of citric greatly affected the properties of the films. The film with C6H8O7·H2O:Ba(NO3)2·6H2O = 6:1 showed best properties after annealed at 850℃for 2 hours, and the grains in the film were apt to arrange in c-axis direction. Ms and Hc of the film reached to about 300 emu/cm3 and 4200 Oe, respectively.We also prepared another soft ferrite Ni0.5Zn0.5Fe2O4 films using Sol-Gel method. The results showed that Ms increased monotonously with the increase of Ta, from 219 emu/cm3 at Ta = 800oC to 334 emu/cm3 at 900℃. However, Hc of the same film first increased with the increase of Ta, and reached to its maximum at Ta = 700℃, then decreased with a further increase of Ta. With the increase of Ta, the variation of Hc can be explained as following: on the one hand, Ni2+ irons in the tetrahedral sites can be moved to the octahedral sites, which caused an increase in magnetic moment and a drop in anisotropy; On the other hand, the grains size increased with increasing Ta resulted in decrease of Hc.Finally, BaFe12O19/Ni0.5Zn0.5Fe2O4 double-layer film was prepared aiming to realize the coupling of hard ferrite and soft one. However, BaFe12O19 phase didn't form due to element diffusion at high annealing temperature. A further study should be taken on this subject in future.
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