Characteristics of the Mn and Co volume-doped acicular γ-Fe ₂O₃ particles

Mn- and Co-doped acicular γ-Fe₂O₃ particles with a coercivity of 923 Oe and Co content of 3.5 wt % have been prepared by a special process. This involves high-temperature ion diffusion, then step annealing. These particles exhibit a high magnetic thermal stability and low-temperature coefficient of coercivity. The latter demonstrates a striking contrast to the ordinary cobalt-body-doped γ-Fe₂O₃ particles. The induced uniaxial anisotropy constant K_u and the magnetocrystalline anisotropy constant K₁ of the particles were determined by torque measurements. The novel properties of these particles are mainly due to the high uniaxial anisotropy, resulting from the anisotropic arrangements of cobalt ions. With the above characteristics and low Co content, these acicular particles can be one of the promising candidates for particulate high-density magnetic recording materials.