Rapid annealing of hexagonal ferrite hard disk for high density recording media with low noise

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High magnetic anisotropy and vety small grain size are necessary for the future high density magnetic recording. In this study, we have focused both Ba- abd Sr-ferrite supttered thin films for ultra high density recording media.We found that Bi addition is effective to lower the crystallization temperature.This results in the suppress of the grain growth and grain size is in the range from 40 to 80 nm at the substrate temperature of 550 C.The grain size of simple hexagonal ferrite films without any additives was in the range from 100 to 150 nm. We found that the addition of Bi can reduce the grain size down to about half. Another experiment on rapid annealing was also carried out for Bi-Ba-ferrite thin films. The grain size can be reduced to 30 to 40 nm by annealing at 750 C for 30 seconds. Coercivity of rapid annealed Ba-ferrite thin films is around 3.7 kOe. The recording characteristics of Ba-ferrite thin film hard disk was evaluated by using merged type magnetic head. The recording density, D50, is in the range from 210 to 230 kfipi. The highest recording density is about 310 kfipi and this bit length almost corresponds to the grain size. This suggests Ba-ferrite thin film disk has high potential for ultra high density recording, when the grain size is reduced to about 10 nm or smaller. Another approach to reduce the grain size should be necessary for the developing Ba-ferrile thin films with nano-scaled grain size.