High quality permanent magnet materials prepared by hot-pressing of very fine ferrite powders

Very fine barium ferrite powders exhibiting good magnetic properties were recently produced by IMI (Israel Mining Industries) employing a special thermochemical process. Conventional sintering of these powders considerably lowered their magnetic properties. A hot-pressing process was therefore developed which yielded dense bulk samples of good magnetic properties. The optimal conditions of this process were found to be: temperature, T = 1000°C, pressure, P = 400 kg/cm
²
and duration time, t = 5 sec. Under these conditions a minimum average grain size of 0.5 μm was achieved giving rise to an intrinsic coercivity of
I
H
c
=4.32 kOe. Partial orientation effects of the hot-pressing process raised the remanence value from B
r
=1.36 kG for the powder to B
r
=2.88 kG for the hot-pressed bulk sample.