A New Perpendicular Magnetic Film of Co–O by Evaporation

Abstract

A new perpendicular magnetic film has been developed by an evaporation method using room temperature substrates. The film is obtained by partially oxidating the Co film with the oxygen gas introduced during deposition. The film structure is a mixture of very fine Co grains and CoO phase. The obtained films have such superior perpendicular magnetic properties as H c⊥=1100 Oe, H k=5.5 kOe and 4πM s=6000 G at Co–45 at%O film composition.

Metal Evaporated Media

“…The saturation magnetization strongly decreases with increasing oxygen content. This is explained by the fact that the oxygen is incorporated into nonmagnetic CoO crystallites (Nakamura et al, 1984;Yoshida and Takayama, 1989). The Co-CoO films are uniaxial with perpendicular anisotropy for all oxygen content.…”

“…Perpendicular coercivities above 1000 Oe are obtained at substrate temperature of 300 C, a deposition rate of 4000 Å /s, and for 20 wt% of Cr which corresponds to the Cr content that maximizes the perpendicular coercivity. Despite these initial results, the development of evaporated CoCr media was hampered by practical issues: it is not easy to control the film composition over a long period of time (Nakamura et al, 1984), and more importantly the substrate needs to be a heat resistant polymer film (typically polyimide film) to withstand the substrate temperatures required to obtain perpendicular magnetic layers (Sugita and Kobayashi, 1982;Sugita et al, 1981). The latter introduces significant additional cost to the medium.…”

“…The latter introduces significant additional cost to the medium. Nakamura et al proposed in 1984 to use evaporation of cobalt under oxygen atmosphere (Nakamura et al, 1984). The evaporation is performed in a multichamber system, with differential pressure from the evaporation chamber to the deposition chamber.…”

“…The Co-CoO films are uniaxial with perpendicular anisotropy for all oxygen content. But the anisotropy constant is maximum at an optimum oxygen content which depends on the film thickness and the deposition parameters (Nakamura et al, 1984;Tateno et al, 1989;Yoshida and Takayama, 1989). Dipolar contributions affect the hysteresis loops such that films with a perpendicular remanence larger than the longitudinal remanence are obtained only at high enough oxygen content.…”

“…Dipolar contributions affect the hysteresis loops such that films with a perpendicular remanence larger than the longitudinal remanence are obtained only at high enough oxygen content. In the work of Nakamura et al (Nakamura et al, 1984), the optimum conditions are found at 45% oxygen content, and lead to a perpendicular magnetic layer with 4pM s ¼ 6000 G, H c ¼ 1100 Oe, H k ¼ 5.5 kOe. The magnetic properties directly relate to the magnetic layer structure.…”