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

Abstract

Validity of values of thermal stability factor K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">beta</sub> (=K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> V/kT) and switching field H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cro</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o </sub> change by w steeply and are significantly different from conventional values: C of 0.5 and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> of 1times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> Hz. Those conventional values lead to 10% or larger values of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cro</sub> and K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">beta</sub> . 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cro</sub> and K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">beta</sub> in a range from 90% to 110% of the correct values