To provide a bit-patterned perpendicular magnetic recording medium consisting of an array of FePt magnetic nanoparticles, the effect of the total dispersant concentrations of oleylamine and oleic acid in a FePt-nanoparticle/toluene coating solution on a selfassembled nanoparticle array with a long-range periodicity on a flat SiO 2 /Si substrate and two patterned substrates, respectively, was examined. At a surfactant concentration greater than 0.8 vol%, FePt nanoparticles with an average size of 4.4 nm were arrayed in a two-dimensional and hexagonal-close-packed ordered array with 8.3-nm pitches on the flat surface. Self-assembled nanoparticles were arrayed on the bottom surface of the patterned trench, the array exhibited a hexagonal-close-packed structure. Furthermore the line defects in the arrays are caused by the waviness of the trench walls, and the surface roughness. A hard disk drive (HDD) using a perpendicular magnetic recording system has been continuously developed, and the current areal recording density has achieved 1 Tbit·in −2 , which corresponds to one bit size smaller than 25 × 25 nm 2 . 1 However, a greater areal density is required to handle big data and reduce the electric power consumption by replacing current products with high-performance HDDs. Bit-patterned media (BPM) consisting of isolated magnetic dots are a promising future magnetic recording technology, and the integration of BPM into a heat-assisted magnetic recording (HAMR) or microwave-assisted magnetic recording (MAMR) system is expected to achieve a higher recording density.2 However, the fabrication of bit patterns with a pitch of less than 20 nm in the circumferential direction on a commercial 2.5-or 3.5-inch disk is a major challenge for producing BPM. Electron-beam lithography, nanoimprint lithography, and extreme ultraviolet lithography can usually create fine patterns on a chip with a size on the order of several square centimeters. Such lithographic techniques began with the ultra-large scale integration (ULSI) of integrated circuits (ICs). These techniques are cost effective for ULSI manufacturing but problematic for magnetic memory media owing to the cost (deep-UV and E-beam lithography) or manufacturability (nanoimprinting).On the contrary, nano-patterning using self-assembly has also attracted much attention as a simple and cost-effective method. For example, the self-organization of block copolymers 3,4 and the self-assembly of magnetic nanoparticles 5 have been reported. For nanoparticle fabrication, many methods for synthesizing fine magnetic nanoparticles have been reported, 5 and the current focus has shifted to a method of fabricating a two-or three-dimensional nanoparticle array on a substrate with a size of more than 100 nm. The LangmuirBlodgett technique, 6,7 doctor-blade coating, 8,9 and spin-coating 10,11 have been proposed as methods of fabricating nanoparticles in an ordered array utilizing self-assembly. As in previous study, 12 a picoliter-regulated pipette was used as an apparatus for coating synthesiz...