Switching field distribution and magnetization reversal process of FePt dot patterns

The fabrication of FePt nanodots with a high structural quality and the control of their switching fields are key issues in realizing high density bit pattern recording. We have prepared FePt dot patterns for dots with 15-300 nm diameters by electron beam lithography and re-annealing, and studied the relation between magnetization reversal process and structure of FePt nanodots. The switching field (Hsw) of dot patterns re-annealed at 710 °C for 240 min showed a bimodal distribution, where a higher peak was found at 5-6 T, and a lower peak was found at ~2 T. It was revealed by cross-sectional TEM analysis that the structure of dots in the pattern can be classified into two groups. One group has a high degree of order with well-defined [0 0 1] crystalline growth, and the other group includes structurally-disturbed dots like [1 1 1] growth and twin crystals. This structural inhomogeneity causes the magnetic switching field distribution observed.