I am not an expert in ferrocells and I had to read about them (it is actually the first time I hear the name). As for you, it was very hard to find any source of reliable information.

So here are my two cents (but I may be wrong). First, one does not bend the trajectory of light (in any measurable fashion) with a magnetic field, as photons have no electric charge. However, in a ferrofluid, we have mostly a medium which behaves like a gas. Therefore, the motion of light may be related to Rayleigh scattering.