Switching field distribution of 40 Gbit/in.2 longitudinal media obtained by subtracting thermal agitation of magnetization

Switching field distributions (SFDs), are presented for longitudinal media of ∼40 Gbit/in.2 and the influence of thermal agitation of magnetization is discussed. Two remanence curves were measured at different sweep rates of applied field of ∼10 and ∼108 Oe/s, respectively, and SFD curves were obtained by differentiating the remanence curves. The SFD becomes significantly narrower at the higher field sweep rate. A SFD curve without the effect of thermal agitation was calculated using Sharrock’s equation. The full width at half maximum of the SFD curve at 10 Oe/s, ΔHr/Hr, is 0.45 for an isotropic medium, while that estimated without the thermal agitation effect ΔH0/H0 is 0.24, indicating that the SFD at the recording frequency is nearly half that measured at vibrating sample magnetometer (VSM) time scales. The ΔH0/H0 of the ∼40 Gbit/in.2 medium is much smaller than that of a 15 Gbit/in.2 medium used for comparison, although the ΔHr/Hr is ∼1.4 times larger than that of the 15 Gbit/in.2 medium due to thermal agitation. The value of ΔH0/H0 is not influenced by the uniaxial anisotropy induced by substrate texture KuTX. This result indicates that the KuTX is not effective for reducing SFD at recording frequencies, although the KuTX strongly affects the SFD at VSM times scales. The improvement of recording performance with increasing KuTX may be related to suppression of thermal relaxation of the remanent magnetization at bit transitions, immediately after the writing process.