Substantially spherical magneto-plumbite ferrite (barium or strontium
ferrite) particles are formed from well-dispersed ultra-fine substantially
spherical iron-based oxide and/or hydroxide particles as precursor
particles. The precursor particles are mixed with a colloidal barium or
strontium carbonate (BaCO.sub.3 or SrCO.sub.3), and with small amounts of
a byproduct, such as sodium or potassium chloride (NaCl or KCl) or
hydroxide (NaOH or KOH) or nitrate (NaNO.sub.3 or KNO.sub.3), functioning
as a flux to lower the calcination temperature. The particles are filtered
out of the mixture, dried, and calcined for a time sufficiently long
and/or at a temperature sufficiently high to form magneto-plumbite ferrite
from the precursor particles, and for a time sufficiently short and/or a
temperature sufficiently low to maintain the general spherical shape of
the precursor particles. The particles are used for forming a magnetic
recording media by dispersing the particles in a magnetic paint and
coating the paint onto a substrate, or by dispersing the particles in a
self-supporting material.
