Effect of Intergranular Exchange on the Thermal Stability and Coercive Field of Perpendicular, Single Phase, Exchange Spring, and Coupled Granular Continuous (CGC) Perpendicular Recording Media

Abstract

We performed micromagnetic simulations in order to investigate the effect of intergranular exchange coupling on the magnetic properties of advanced magnetic recording structures. We found that the coercive field of granular recording media decreases with increasing intergrain exchange coupling ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">int</sub> ). We observed this decay even for perfect films without switching field distributions and soft magnetic inclusions. A mean field exchange field of about mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex</sub> = 0.34 T leads to the same thermal stability of the grains at the transition and in the center of a bit. A larger value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">int</sub> lowers the thermal stability of the grains close to the transitions. Micromagnetic simulations of coupled granular continuous (CGC) media indicate that the top layer in CGC media is not continuous. The simulations suggest that the top layer is granular with a relatively weak intergrain exchange coupling, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">int</sub> .