Relationship between the intrinsic thermal switching field at 10 ^-9 s and the anisotropy field in magnetic recording media

Recently, the time dependent remanent coercivity, HCR(t), has become a major concern in new high density recording media where the coercivity at 1 ns can be ~50% larger than that measured at 100 s. To combat this problem, an increase in the anisotropy has typically been used to make the media more thermally stable. However, the effect of increasing the anisotropy on H_CR at short write times has not been well documented. In this paper, new measurements of the anisotropy field from the rotational hysteresis are compared with previous measurements of the intrinsic switching field in a variety of particulate and thin film media. All of the particulate media have intrinsic switching fields of H₀~H_K/3 independent of particle size or orientation. In contrast to the particulate samples, the thin film samples have a larger ratio of H₀/H_K from 0.5 to 0.8 possibly indicating a change in reversal mode from incoherent to coherent rotation. Further, results on γ-Fe₂ O₃ particulate samples confirm that below a few nanoseconds, thermal switching ceases to drive the increase in H_CR (t)