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A soft magnetic CoNiFe film with high saturation magnetic flux density and low coercivity

Nature volume 392, pages 796–798 (1998)Cite this article

Abstract

Magnetic materials are classed as ‘soft’ if they have a low coercivity (the critical field strength Hc required to flip the direction of magnetization). Soft magnetic materials are a central component of electromagnetic devices such as step motors, magnetic sensors, transformers and magnetic recording heads. Miniaturization of these devices requires materials that can develop higher saturation flux density, Bs, so that the necessary flux densities can be preserved on reducing device dimensions, while simultaneously achieving a low coercivity. Common high-Bs soft magnetic films currently in use are electroplated CoFe-based alloys1,2,3,4 electroplated CoNiFe alloys5,6,7 and sputtered Fe-based nanocrystalline8,9,10,11 and FeN films12,13,14. Sputtering is not suitable, however, for fabricating the thick films needed in some applications, for which electrochemical methods are preferred. Here we report the electrochemical preparation of a CoNiFe film with a very high value of Bs (2.0–2.1 T) and a low coercivity. The favourable properties are achieved by avoiding the need for organic additives in the deposition process, which are typically used to reduce internal stresses. Our films also undergo very small magnetostriction, which is essential to ensure that they are not stressed when an external magnetic field is applied (or conversely, that external stresses do not disrupt the magnetic properties). Our material should find applications in miniaturization of electromechanical devices and in high-density magnetic data storage.

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Figure 1: Three-element maps showing compositions of our CoNiFe films.
Figure 2: High-resolution transmission electron micrograph of the electroplated HB-CoNiFe film.
Figure 3: Anodic polarization studies.

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Acknowledgements

We thank Y. Okinaka, Waseda University, for discussions. This work was supported by a Research for Future Project of the Japan Society for Promotion of Science, a Grant-in-Aid for Scientific Research on Priority Area from the Ministry of Education, Science, Sports and Culture, Japan, and the Storage Research Consortium (SRC).

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Authors and Affiliations

  1. Department of Applied Chemistry, Waseda University, and Kagami Memorial Laboratory for Material Science and Technology, Waseda University, Shinjuku-ku, 169, Tokyo, Japan

    Tetsuya Osaka, Madoka Takai & Katsuyoshi Hayashi

  2. NEC Ibaraki Ltd, Sekijomachi, Makabegun, 308-01, Ibaraki, Japan

    Keishi Ohashi

  3. NEC Corporation, Fuchu, 183, Tokyo, Japan

    Mikiko Saito & Kazuhiko Yamada

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  1. Tetsuya Osaka
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  6. Kazuhiko Yamada
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Correspondence to Tetsuya Osaka.

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Osaka, T., Takai, M., Hayashi, K. et al. A soft magnetic CoNiFe film with high saturation magnetic flux density and low coercivity. Nature 392, 796–798 (1998). https://doi.org/10.1038/33888

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