  We present a semi-phenomenological treatment of light transmission through
and its reflection from a ferrofluid, which we regard as a magnetically tunable
system of dense random dielectric scatterers with weak dissipation. Partial
spatial ordering is introduced by the application of a transverse magnetic
field that superimposes a periodic modulation on the dielectric randomess. This
introduces Bragg scattering which effectively enhances the scattering due to
disorder alone, and thus reduces the elastic mean free path towards Anderson
localization. Our theoretical treatment, based on invariant imbedding, gives a
simultaneous decrease of transmission and reflection without change of incident
linear polarisation as the spatial order is tuned magnetically to the Bragg
condition, namely the light wave vector being equal to half the Bragg vector
(Q). Our experimental observations are in qualitative agreement with these
results. We have also given expressions for the transit (sojourn) time of light
and for the light energy stored in the random medium under steady illumination.
The ferrofluid thus provides an interesting physical realization of effectively
a "Lossy Anderson-Bragg" (LAB) cavity with which to study the effect of the
interplay of spatial disorder, partial order and weak dissipation on light
transport. Given the current interest in propagation, optical limiting and
storage of light in ferrofluids, the present work seems topical.
