MAGNETIC INTERACTION BETWEEN IRON-OXIDE CLUSTERS PRECIPITATED IN SILICATE-GLASSES

Annealing of 20CaO . 20SiO(2) . 7Fe(2)O(3) . 6FeO glasses at 973 K in vacuo produced clusters of a nonstoichiometric solid solution between Fe3O4 and gamma-Fe2O3. The growth of clusters proceeded by diffusion o f iron ions and the predominant diffusant was Fe3+ ions, The phase of the clusters approached gamma-Fe2O3 as the annealing time increased, M ossbauer spectroscopy revealed that these clusters had magnetic moment s and showed superparamagnetism above the blocking temperature. It has been shown that the dipole interaction between two nearest clusters i s smaller by a factor of 1/7 than the magnetocrystalline anisotropy en ergy. This indicates that the direction of the magnetic moment is pred ominantly determined by the magnetocrystalline anisotropy below the bl ocking temperature. (C) 1996 American Institute of Physics.