Magnetic anisotropy and switching field of spindle-shaped metal particles for particulate recording media

Abstract

The difference of magnetic properties between spindle- and needle-shaped metal particles, which have almost the same thickness of about 17–27 nm, is discussed through a magnetic torque analysis for particulate films made of these metal particles. The effective magnetic anisotropy field of particles H ptc k(eff) are 6.3 and 6.5 kOe (averaged values), respectively, for spindle- and needle-shaped metal particles, showing no significant difference. Because of the interparticulate magnetostatic coupling, these H ptc k(eff) values are estimated to be about 1 kOe smaller than intrinsic values of shape anisotropy field. Saturation magnetization M s in both kinds of metal particles is found to show almost the same value of about 1300 emu/cm 3. However, the switching field H EA r normalized by H ptc k(eff) of the spindle-shaped particles is about 10–15% larger than that of the needle-shaped particles. Furthermore, the value of SFD of the spindle-shaped particles is about 20% smaller than that of the needle-shaped particles. The values of H EA r/ H ptc k(eff) and rotational hysteresis loss R h in both kinds of metal particles are strongly related to the thickness of particles, however, significant differences in these relations between spindle- and needle-shaped metal particles were not observed.