Alumite disc using anodic oxidation.
T Tsuya, T. Tokushima, Makoto Shiraki, Yuko Wakui, Yasutoshi Umehara, Hajime Nakamura, Y. Katsumata, Yoshitaka Saito · Journal of the Magnetics Society of Japan · 1987
Details are given of a method of measuring perpendicular magnetic alumite discs using anodization with an additional new process called “pore widening” which is effective in controlling the coercive force. Electro-deposited fine iron needles were in a single crystalline state, and the perpendicular orientation of magnetization was confirmed. The resulting magnetic recording characteristics of the rigid discs were satisfactory, indicating usefulness of the method as a perpendicular recording medium.