Thermal annealing of [Fe 1.65 nm/Pt 1.84 nm](50) multilayers at 673 K for various annealing times between 60 and 12000 s leads to the direct formation of the fully ordered L1(0) FePt phase with (111) texture. The average grain sizes, determined from X-ray diffraction size-strain analysis, are smaller than the critical size for multidomain FePt particles, suggesting the presence of single-domain (SD) grains. The coercivity increases with annealing time and increasing grain size and reaches values of about 955 kA/m. The remanence values are typical for randomly oriented weakly-interacting particles. A decrease of the remanence with annealing time suggests a decrease of the intergrain exchange interactions with annealing time. Analysis of minor loops and the initial magnetization curves shows the presence of a broad distribution of critical fields, which the individual SD particles have to overcome for the magnetization reversal. (C) 2010 Elsevier B.V. All rights reserved.