Magnetization reversal process and bistability of $Co∕Pt$ multilayer dot

Magnetization reversal process and the critical diameter $dc$ for single and multidomain of $Co∕Pt$ multilayer dot were investigated by detecting anomalous Hall effect of a single dot with diameter $d$ ranging from $100to1000nm$⁠. The perpendicular anisotropy constant $Ku$ was varied from $1.3×107to2.6×107erg∕cc$ by changing the Co layer thickness. The dominant magnetization process for the dots with $d⩾1000nm$ was domain wall displacement, while nucleation of a reversed embryo governed the reversals in the dots smaller than $500nm$⁠. The $dc$ for stable single domain increases with $Ku$ from $150nm$ to larger than $1000nm$⁠. This behavior is mainly due to the increase of domain wall energy owing to the increase of $Ku$⁠, and the $dc$ coincides very well with the domain size of continuous films.