Longitudinal recording performance of sputtered barium ferrite media on a carbon rigid disk substrate

We report the first measurement of the longitudinal magnetic recording properties of as-deposited crystalline thin film barium ferrite media. Using facing target sputtering, randomly oriented crystalline barium ferrite (BaFe₁₂O₁₉, BaM) has been deposited onto an Ultra Densified Amorphous Carbon substrate, producing high quality films in-situ at a substrate temperature of 660°C without any post-deposition annealing. In order to prevent diffusion of carbon into the BaM film, an underlayer of silicon nitride was first reactively sputtered. The BaM sputtering was carried out using targets made from substituted BaM powder which had a powder H_c=1860 Oe (from Toda Kogyo) in a 10% O₂/Ar gas mixture at 3 mTorr. The sputtered films had an in-plane H_c=2100 Oe. The performance of the disk was compared to a commercial disk with cobalt alloy media with H_c=1760 Oe. At a flying height of 75 nm the isolated pulse width, PW₅₀, was 0.67 μm vs. 0.88 μm for the commercial media using a ReadRite M84 thin film head with a gap of 0.3 μm. Near its measured D₅₀ of 66 kfci the BaM media had a broad band signal/noise ratio (SNR) of 20 dB vs. 13 dB for the commercial media