Cobalt--Ferrous ferrite with re-entrant hysteresis loop

If the field H
r
required to initiate flux reversal exceeds the H
w
required to continue reversal, a re-entrant hysteresis loop results. This has been observed in magnetically annealed cobalt-ferrous ferrites in which H
r
at 10 to 20 Oe may be as high as
1.5 \times H_{w}
at room temperature. Frequently, these ferrites are bistable and show no minor loops. Flux reversal appears to involve only one domain wall, giving rise to high squareness but slow switching ; typical values for a 12-mm toroid are
R_{s} = 0.99
and
s = 540 \mu
s Oe. Intermediate stabilized magnetization states have been introduced into these materials by a simple annealing procedure. Switching now occurs between three or more magnetization states, providing the basis for a multistable device. Details of preparation and measurement are given and the results discussed in terms of various models.