The measurement of the anisotropy field of single "tape" particles

The uniaxial anisotropy field H
a
of nominally single acicular particles was measured by three different methods, and the coercivity was also found. A very dilute suspension was made in a viscous liquid, and a particle observed with the microscope. Various types of magnetic field were then applied, and the particle's change in orientation enabled
H_{a}, H_{c}
and/or H
r
to be determined. One method gave anomalously low values for H
a
, but it was possible to reconcile the results. The larger values lay in a range consistent with the chain-of-spheres and prolate ellipsoid models. There was a linear relationship between H
a
and H
r
(or H
c
). The results suggested new reversal mechanisms.