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 ∼10 8 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, ΔH r/H r, is 0.45 for an isotropic medium, while that estimated without the thermal agitation effect ΔH 0/H 0 is 0.24, indicating that the SFD at the recording frequency is nearly half that measured at vibrating sample magnetometer (VSM) time scales. The ΔH 0/H 0 of the ∼40 Gbit/in. 2 medium is much smaller than that of a 15 Gbit/in. 2 medium used for comparison, although the ΔH r/H r is ∼1.4 times larger than that of the 15 Gbit/in. 2 medium due to thermal agitation. The value of ΔH 0/H 0 is not influenced by the uniaxial anisotropy induced by substrate texture K u TX. This result indicates that the K u TX is not effective for reducing SFD at recording frequencies, although the K u TX strongly affects the SFD at VSM times scales. The improvement of recording performance with increasing K u TX may be related to suppression of thermal relaxation of the remanent magnetization at bit transitions, immediately after the writing process.
ASJC Scopus subject areas
- Physics and Astronomy(all)