This paper describes detailed studies of the effects of size distribution on the easy axis alignment of L10-FePt nanoparticles synthesized by the recently developed “SiO2-nanoreactor” method (Appl. Phys. Lett. 87 032503 (2005)). The steady state orientation of the easy axis of the L10-FePt nanoparticles of the L10-FePt/polystytene composite, which had been prepared at 60°C under an external field of 50 kOe, was analyzed with particular emphasis on the effects of size distribution. Analyzes that did not take account of size distribution resulted in very limited success. To quantitatively estimate the effects of size distribution, the size dependency of particle magnetization, which originates not only in changes in particle volume but also in the size dependency of saturation magnetization, was considered. Such analyzes of the rocking curve of the L10-FePt/polystytene composite, which had been measured by using the (002) diffraction peak of the L10-FePt, resulted in quantitative determination of the steady-state orientation of the easy axis of the L10-FePt nanoparticles. It was revealed that about 50% of the L10-FePt nanoparticles have angles of less than 13 degrees between the magnetic easy axis and the external magnetic field.
