S. Kantake

Co ferrite films with excellent perpendicular magnetic anisotropy and high coercivity deposited at low temperature

The present article describes CoxFe3−xO4 films, which were fabricated at 90 °C by the ferrite-plating method and have the excellent perpendicular magnetic anisotropy and the perpendicular coercivity Hc⊥ above 2 kOe. The films were composed of Co ferrite and Fe3O4 grains. The highest Hc⊥ reached 3 kOe at the composition of Co0.43Fe2.57O4 and the saturation magnetization Ms was 500–550 emu/cc. Hc⊥ was over 2 kOe even for a film thickness of 35 nm without any underlayers. ΔM⊥ evaluation that is measured in the perpendicular direction to the film plane showed that the interactions in the films supported the magnetized state, stabilizing the direct current remanent state. The Mossbauer analyses revealed that the Co0.43Fe2.57O4 films have excellent perpendicular magnetic anisotropy and the magnetization direction inclined from the perpendicular axis due to the demagnetization field. This achievement will open the way to develop the high-density perpendicular recording media even when plastic disks and sheets ar...

Spin-spray ferrite-plated Co ferrite films with high coercivity for perpendicular magnetic recording media

Effects of plating conditions on Co ferrite-plated films for perpendicular magnetic recording media were investigated to increase coercivity H/sub c/spl perp// and remanence ratio (M/sub r//M/sub s/)/sub /spl perp// in the plane perpendicular to the film. By optimizing a concentration of NaNO/sub 2/ in an oxidizing solution and the deposition rate, Co-Ni ferrite films with H/sub c/spl perp// of 3200 Oe and (M/sub r//M/sub s/)/sub /spl perp// of 0.6 were obtained without any heat-treatment. Disk media with higher H/sub c/spl perp// and (M/sub r//M/sub s/)/sub /spl perp//, exhibited reproduced waveforms of di-pluses shape and better frequency responses than that with lower /sub c/spl perp// and (M/sub r//M/sub s/)/sub /spl perp//. Media noise did not increase with increasing frequency, suggesting that the transition noise was low.

Sputter-deposition Of Co-Cr-Ta Alloy Layers On Ni-Zn Ferrite Plated Underlayers

The influence of Ni-Zn ferrite plated underlayers on grain size and magnetic characteristics of sputter-deposited Co-Cr-Ta layers was investigated. These properties were found to be strongly influenced by the surface texture of the underlayers. When the grain size of the underlayers was large (200-300 nm), the grains in the Co-Cr-Ta layers seemed to aggregate and were not isolated clearly. When the grain size of the underlayers was small (50-70 nm), the grain size in the Co-Cr-Ta layers decreased and the perpendicular coercivity increased to over 2 kOe. Further studies showed RF sputter-etching of the underlayers reduced grain size (30/spl sim/50 nm), and increased perpendicular coercivity (3.0 kOe), presumably through a reduction of surface roughness and a formation of many fine nodules on the underlayers, which play a role of nucleation sites for the Co-Cr-Ta grains.

Intergranular coupling and activation volume of Co-Ni ferrite thin films with high coercivity above 3 kOe

Co-Ni ferrite film media with high coercivity above 3 kOe were fabricated by ferrite plating and intergranular coupling and medium noise were discussed. Increase of Co content in Co-Ni ferrite thin film with a thickness of 40 mn led to a decrease of intergranular exchange coupling and activation volume, resulting in the reduction of media noise in the high frequency region. The coercivity H/sub c/ increased with the Co content, and reached 3.6 kOe. At the maximum Co content, the activation volume took the minimum value of 6.7/spl times/10/sup -18/ cm/sup 3/, being smaller than the volume of a single grain in the film. The medium noise was kept almost constant up to the linear recording density of 144 kfrpi, while the noise of the media with the lower Co content and lower H/sub c/ increased with the linear recording density.