Validity of Values of Thermal Stability and Switching Field in Recording Medium Obtained by Using Sharrock´s Formula

Validity of values of thermal stability factor K_beta (=K_uV/kT) and switching field H_cro in perpendicular recording medium obtained by Sharrock´s formula has been analyzed using micromagnetic simulation. The following was found. Time-dependent remanent coercivity can be expressed by Sharrock´s formula for media with the inter-grain exchange coupling w in a wide range. The values of the exponent C and the attempt frequency f_o change by w steeply and are significantly different from conventional values: C of 0.5 and f_o of 1times10⁹ Hz. Those conventional values lead to 10% or larger values of H_cro and K_beta. It was also found that field error less than 20 Oe is required for conventional VSM measurement or field calibration within 100 Oe is required for VSM with 1 mus-pulse field measurement to obtain H_cro and K_beta in a range from 90% to 110% of the correct values