Thermal aftereffects in thin film magnetic recording media

Thermal aftereffects in written bits in CoCrPt thin film magnetic recording media are examined using a magnetoresistive (MR) head and a magnetic force microscope (MFM). Decays in signal output over time at room temperature in media with very thin magnetic layers of about 14-nm thickness or less were observed by using an MR head. The decay in signal output was accompanied by an increase in medium noise. Even with a precise examination of cross-track profile using an MFM, no change in track width caused by thermal aftereffects can be detected. Thermal decay of the signal output in a 14-nm thick magnetic layer with small remanence thickness product M_rt_mag of about 40 G-μm was successfully reduced by increasing the platinum content in the CoCrPt magnetic layer or by adding boron to the CrTi underlayer without increasing the medium noise. The reduction of thermal decay is considered to be caused by the increase of magneto crystalline anisotropy and increase in magnetic-crystal-grain size. These results suggest that it is possible to reduce the medium noise without reducing the crystal grain size and without much degradation of thermal stability even for media with small M_rt_mag which is needed to achieve a recording density of 10 Gb/in²