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 15–300nm 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 240min showed a bimodal distribution, where a higher peak was found at 5–6T, and a lower peak was found at ~2T. 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 [001] crystalline growth, and the other group includes structurally-disturbed dots like [111] growth and twin crystals. This structural inhomogeneity causes the magnetic switching field distribution observed.