The effect of aging on erasure in particulate disk media

The effect of aging and heating on the erasability of particulate hard disks made from γ-Fe₂O₃ and surface modified Co-γ-Fe₂O₃ was studied. A 1-MHz square wave signal was recorded on particulate hard disks rotating at 3600 r.p.m. using a ferrite inductive head. The recorded signal was measured as a function of the AC erase field before and after heating the disks in ovens at temperatures ranging from room temperature to 200°C for times ranging from 10 min to several months. The erasability of the Co-γ-Fe₂O₃ hard disks heated for one week decreased with increasing heating temperature, which was especially evident at the higher erase fields. An Arrhenius plot of signal strength versus inverse absolute temperature gave an activation temperature of 0.2 eV. For the γ-Fe₂O₃ disks there was a decrease in the erasability of 2 dB at an erase field of 800 Oe and 8 dB at 900 Oe after heating. Vibrating sample magnetometer and ferromagnetic resonance spectrometer measurements were made to obtain the magnetic parameters before and after heating