Magnetic grain size reduction by using oxygen exposure process onto very thin islandlike WCr seedlayer in longitudinal recording media

To reduce the grain size and the media noise in CoCrPtB/CrMo longitudinal media, a sputtering process which includes the exposure of oxygen onto the surface of a very thin (0.5 nm) WCr50 seedlayer has been developed. The purpose of oxygen exposure onto the seedlayer surface is to enhance the nucleation sites of the seedlayer. It is found that (a) the exposure of 25 and 100 L (1 L corresponds to the adsorption of one layer of the oxygen atom when the sample is exposed to oxygen atmosphere) of oxygen onto the seedlayer reduces the mean grain diameter of the magnetic film from 8.3 to 7.5 and to 7.0 nm, respectively, (b) the exposure of 25 and 100 L of oxygen onto the seedlayer decreases the media noise by 15% and 45% and improves the media signal to noise ratio by 1.5 and 5 dB, respectively.