Erasure processes of magnetic memories at the microscopic level

The microscopic erasure characteristics of the most common types of magnetic storage media have been investigated using magnetic force microscopy. The micromagnetic evolution of recorded patterns on thin film rigid disk and flexible media have been observed as a function of an applied external field, and the reduction of magneto-optic media marks has been investigated as a function of heating temperature. Specific stages of the erasure process exhibit unique characteristics for each medium. The initial erasure stages for both types of ferromagnetic media show similar behaviour and are characterized by the expansion of the favoured domains. The middle and final stage behaviours are markedly different. For the thin film case, magnetization reversal occurs by nucleation and growth while for the particulate media, reversal occurs primarily through localized cluster switching. These results were correlated with their macroscopic magnetization curves and their diverging characteristics can be attributed to their differing interparticle coupling interaction. The initial stage of erasure of magneto-optic media is accompanied by the anisotropic displacement of the domain walls which introduces shape irregularities of the original circular marks. With increase in temperature, the microdomains that comprise the individual marks become apparent as each microdomain independently diminish in size. Pinning at the mechanical grooves has been found to be mainly responsible for retarding domain collapse.