COERCIVITY OF POROUS ACICULAR PARTICLES

It has been suggested that the porosity in the magnetic particle has the crucial effect upon observed low coercivity, as compared with predictions of single-domain theory. However, the influence of the inner pores was never theoretically analyzed. When interactions among the pores are considered, we found that the coercivity of a single-domain particle depends on not only the porosity but also the number of pores. Moreover, in some cases the porosity increases the coercive force, in others it decreases it. When the pore number is large, the relationship between coercive force and porosity is quite linear. The magnetization of the particle is always decreasing as porosity increases. It was also found that the oblique angle between the inner pore and magnetic particle results in the decrease of the coercivity. To increase the coercivity, it is concluded that the pore shape is more important than the reduction of the porosity and the alignment of the pore.