Hideo Suda1, Tohru Watanabe2, Yoshinari Misaki2 and Yoshimi Tanabe2
1Department of Industrial Chemistry, Faculty of Technology, Tokyo Metropolitan University, Tokyo. Present address: Nippon Shiken Dental Co. Ltd., Tokyo
In previous papers, we reported that increasing the reducing agent (NaBH4) added into a plating bath resulted in an increase of boron content in the electroless plating Ni-B alloy film, and the structure of the obtained plating film changed continuously as follows:
\noindent (1) crystal (aggregation of fine crystals)→ (2) quiet fine crystals+amorphous phase→ (3) amorphous phase+quiet fine crystals→ (4) amorphous phase. The microstructure of the Ni-B alloy film deposited by using dimethylamine borane (DMAB) as the reducing agent was also dependent upon concentration of reducing agent in a plating bath. Even in the alloy film with the highest boron concentration, however, it was not a homogenious amorphous phase and contained a very small amount of quiet fine crystals. We called this structure the ``amorphous-like structure''.
In this investigation, the crystallization process by heat treatment and the magnetic properties of these Ni-B alloy films were studied. The crystallization temperature of Ni3B from the amorphous phase was 583 K, but below this temperature fine nickel crystals which alredy existed in the as-deposited amorphous-like phase were grown by annealing. Annealing at 623 K crystallized the retained amorphous phase under the nucliation process. The final stable structure of this alloy film was the aggregation of nickel and Ni3B crystals. Furthermore, the amorphous-like Ni-B alloy film showed the anomalous magnetic phenomena as reported in our previous paper that the magnetization vs temperature curve cannot be fitted to the Brillouin function but can be dscribed as a linear or smoth curve which is concave upwardes, although the Ni-B alloy film is feromagnetic.
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