Magnetic force microscopy studies of bit erasure in particulate magnetic recording media

Magnetic force microscopy (MFM) with in situ magnetic fields has been used to study the erasure of bit transitions in high-density particulate magnetic recording media. The erasure of the bit magnetization pattern was studied by imaging the bits in a sequence of applied magnetic fields, each separated by about 250 Oe. It was found that the largest change in the bit patterns between two subsequent images occurred when the field was increased to 1.4 kOe, a field value close to the measured bulk coercivity of 1.6 kOe. The reversals occurred mostly around regions with irregular magnetic boundaries. In addition, there was an observation that reversal was more likely to occur in smaller fields in those regions of the disk which exhibited a larger than average surface roughness. A qualitative analysis of the erasure indicates a magnetization process similar to that observed by Walsh et al. (J. Appl. Phys. 84 (1998) 5709) in thin film recording media.