Dot Size Dependence of Magnetization Reversal Process in ${\rm L}1_{0}$ -FePt Dot Arrays

The dot size dependence of the magnetization reversal process in perpendicularly magnetized L1₀-FePt dot arrays has been investigated in terms of minor loop measurement and magnetic domain observation. For the dots with diameters of 0.25 and 1 mum, the initial applied field (H_in ^sat) required to saturate the coercivity in the minor loop starting from the thermally demagnetized state is smaller than saturated coercivity (H_c ^sat), indicating a typical nucleation-type magnetization reversal process. For the dots with diameters of 2.3 and 5 mum, on the other hand, H_in ^sat is larger than H_c ^sat. The magnetic force microscopy images show that the field to wipe out domain walls increases with the dot size, which is consistent with minor loop measurements. The phenomenological analysis for the dots with diameters of 0.25 and 1 mum indicates that irrespective of the dot size the annealing reduces the size of the defect regions and leads to the enhancement of the coercivity due to the recovery from the microfabrication damage.