Figure 2. Particle size dependence of the magnetic properties.

(a) Magnetic hysteresis loops of S-1020, S-1044, S-1063, and S-1142 measured at 300 K with an illustration of the average particle size. (b) H_c value at 300 K with random orientation versus d plot. The red line is a guide for the eye, which was drawn based on the d dependence equation of H_c, taking into account the random orientation and particle size distribution. The d_p (superparamagnetic limit) value was calculated to be 7.5 nm. The H_c versus d plots at room temperature of BaFe₁₂O₁₉ (blue), SrFe₁₂O₁₉ (green), and CoFe₂O₄ (purple) are also shown.