Effects of Cr and magnetic bias on read/write and noise characteristics of CoCrTa/Cr longitudinal thin-film media

Abstract

The effects of Cr and magnetic bias on read/write and noise characteristics of CoCrTa/Cr longitudinal thin-film media were investigated. Samples of magnetic thin films were prepared by using dc magnetron sputtering at four different substrate-bias conditions: no bias (N), Cr bias only (C), magnetic bias only (M), and both Cr and magnetic bias (CM). Magnetic properties, parametrics, media noise, signal-to-noise ratio (SNR), nonlinear transition shift (NLTS), crystallography, and microstructures were studied. Comparison of read/write characteristics measured with a magnetoresistive head at 72.4 kfci recording density showed improvement in resolution and pulse width for the media sputtered with M and CM bias. When the magnetic layers were sputtered with no bias, it was found that the Cr bias had almost no effect on media noise or SNR. However, the application of magnetic bias individually and substrate bias during both Cr and magnetic deposition reduced media noise about 20% and 30% and increased SNR about 5 and 7 dB, respectively, at 136.4 kfci recording density. NLTS was studied as a function of linear recording density for all these four samples. It was observed that the M and CM bias-sputtered media produce lower NLTS which correlates very well with the corresponding media noise. Co(11.0) and Co(10.0) peaks of magnetic films sputtered with M and CM bias showed broader peak width which produces smaller grain size of magnetic film for reduced transition noise. Transmission electron microscope images did not exhibit significant difference in microstructure between the films prepared by sputtering with or without applying substrate bias.