MAGNETIC-PROPERTIES OF BORON AND COBALT DOPED IRON-OXIDE PIGMENTS PREPARED FROM OXALIC PRECURSORS

To obtain particles with required morphological and magnetic characteristics for high density recording, we have prepared via oxalic precursors cobalt substituted (1-x)Fe3O4·(λ-Fe2O3) particles soped by boron (0.2 wt%). These particles have an average length of 0.15 to 0.2 μm, an average acicularity of 3 to 4 and specific surface areas of 15 m2/g. The variations of coercivities, remanent and saturation magnetizations were studied as a function of oxidation temperatures. For partially oxidized magnetites substituted by 2 wt% of cobalt, we have obtained coercivities up to 730 Oe with remanent and saturation magnetizations of 37 and 76 emu/g, respectively. The coercivity temperature dependence factor is only -4.1 Oe/°C and that is near the common values for cobalt surface-doped oxides having the same coercivity. © 1990.