Ba–ferrite thin-film disk for perpendicular magnetic recording

Abstract

The authors have prepared Ba–ferrite film disks and evaluated their magnetic read/write characteristics. The c-axis-oriented Ba–ferrite thin films were formed epitaxially on c-axis-oriented ZnO films by means of a targets-facing-type sputtering system. The direction of easy magnetization in the film with perpendicular crystalline anisotropy is almost perpendicular to the film plane. Thus, the perpendicular remanence is more than 60 times as large as the in-plane one. The simple Ba–ferrite films, however, have a coercive force, Hc⊥ above 2 kOe which is too large to write on by means of a conventional head. The substitution of In3+ in the Ba–ferrite films makes the Hc⊥ values decrease to about 1 kOe without increasing the critical temperature, Tcritical, of c-axis orientation. The read/write characteristics of the films were measured with a MnZn–ferrite ring head. The reproduced signal exhibits clear dipulsive waveforms as the dipulse ratio exceeds 0.7. Furthermore, the overwrite ratio decreases below −28 dB for the In3+-substituted Ba-ferrite film disk. The Ba–ferrite film disks have promising potential as a high-density perpendicular magnetic recording medium.