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
_u
V/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 1times10
⁹
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