Nonlinear effect of small volume fraction on the coercivity for acicular particles

Origins of nonlinear dependence of the coercivity on the volume fraction for an assembly of acicular particles are investigated. For a very small volume fraction, the nonlinear relationship between the coercivity and the volume fraction is attributed to the nonuniform distribution of particles and the surface effects. Considering the influence of surface, we find the coercivity can be either increasing or decreasing for a small volume fraction with different surface anisotropy constant Ks. Observed results agree with predictions based on the present model.