Magnetic measurements on single acicular particles of γFe2O3

Measurements of the remanent coercive force H
r
have been made upon large numbers of individual 'tape' particles of γFe
2
O
3
. The greatest range of values of H
r
sound for any one sample was 300r
<1100 0e, and other samples of different origins gave rather similar results. Using the data for two sets of samples, together with other known factors, the remanent loops of the corresponding tapes were synthesized. The synthesized loops resembled the experimental loops, but the remanent coercive forces were larger by 20 to 60 0e: very good agreement was obtained for one sample. The effect of a.c. demagnetization was investigated. This showed that particles of the highest H
r
were undoubtedly single, but that many of lower H
r
were multiple. Particles of similar morphologies have been observed in recording tape. A value for H
r
of 1100 0e is shown to be consistent with the magnetization reversing by the buckling process.