  Random orientation of liquid-suspended magnetic nanoparticles (Ferrofluid)
gives rise to zero net magnetic orientation. An external magnetic field tends
to align them into clusters, leading to a strong linear dichroism on a
propagating wave. Using 10 nm-sized Fe3O4, we experimentally realize a
polarization-sensitive magnetic modulator operating at terahertz wavelengths.
We reached a modulation depth of 66% using a field of 35 mT. The proposed
concept offers a solution towards fundamental terahertz magnetic modulators.
