Dielectric behaviour of a ferrofluid subjected to a uniform magnetic field

The electric susceptibility of samples of ferrofluids subjected to a uniform magnetic field
H
was measured. The electric susceptibility
\chi
is dependent on the magnitude of the magnetic field and on the relative direction between the electric field
E
and the magnetic field
H
. 1) When
E
is perpendicular to
H, \frac{\partial\chi_{\perp}}{\partialH} < 0
2) When
E
is parallel to
H, \frac{\partial\chi_{\parellel}}{\partialH} > 0
These results have been interpreted as a magneto-electric directive effect. A model is proposed, based on the assumption that the magnetic particles are roughly ellipsoidal and conducting grains.