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 ∼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.