AIP Digital Archive
The high-vacancy-content ferrites represented by x(MFe2O4)⋅y(Fe3O4)⋅z(γ-Fe2O3), where x+y+z=1 (z(approximately-greater-than)0.50), were obtained in the clear and strongly alkaline solutions of Fe(III) and M(II) tartrate [M(II)=Zn(II), Ni(II), and Cd(II)] or dextrose at 100 °C. The vacancies were replaced with the bivalent metal ions in the reaction solutions, and the replaced number increased with an increase in the concentration of the bivalent metal ions. The ferrite particle size was dependent on the bivalent metal species and the content (x,y). The Fe(II) ions enhanced the crystal-growth rate. The particle size of the magnetites (x=0) increased from 100 to 800 A(ring) with an increase in the Fe(II) ion content (y=0.10–0.35). The high-vacancy-content magnetite was transferred from superparamagnetic to ferrimagnetic particles as the size increased. The Zn(II), Ni(II), and Cd(II) ions did not enhance the growth rate so much as compared to the Fe(II) ions. The particle sizes were less than 200 A(ring), and most of the particles were superparamagnetic. The saturation magnetizations were lower than the theoretical values, and increased with an increase in the particle size, indicating the surface effect.
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