Magnetic thermal stability of Mn and Co volume-doped acicular iron oxide particles

The magnetic thermal stability of Mn and Co volume-doped acicular /spl gamma/-Fe/sub 2/O/sub 3/ particles was studied. These MnCo-/spl gamma/-Fe/sub 2/O/sub 3/ particles with a coercivity about 950 Oe and Co content about 3.5 wt.% have been prepared by high temperature ion diffusing and step annealing. The MnCo-/spl gamma/-Fe/sub 2/O/sub 3/ particles exhibit a much higher transverse field stability than that of Co-/spl gamma/-Fe/sub 2/O/sub 3/ particles. The induced effective uniaxial anisotropy constant, K/sub u/ and the magnetocrystalline anisotropy constant, K/sub 1/ of the particles were determined by the analysis of torque curves. The high magnetic thermal stability of these particles is mainly due to the higher and more stable induced uniaxial anisotropy, which is the result of the anisotropic arrangements of cobalt ions promoted by the presence of manganese ions during the step annealing. The MnCo-/spl gamma/-Fe/sub 2/O/sub 3/ particles show a smaller irreversible decrease of uniaxial anisotropy with temperature and time in a magnetic field.<
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