Use of anisotropy of light transmittance in a system to measure the frequency of nanowires' rotation in a viscous liquid

Fe nanowires with diameters of ca. 80 nm and lengths ranging from 1 to 3 μm were immersed in a viscous liquid and exposed to a static magnetic field in order to orient them in a specific direction. The nanowire suspension was illuminated with a laser beam. The light intensity was measured at the input and output. It was observed that the light transmittance of the nanowire system was strongly dependent on the nanowires' orientation in relation to the laser beam. The phenomenon was applied to measure the rotation frequency of the nanowires immersed in a liquid with a viscosity of 2 Pa·s. Rotation of the nanowires was enforced by a rotating magnetic field generated by a rotating magnet. On the basis of the obtained results it was observed that the highest frequency of the nanowires' rotation in the applied liquid, in a rotating magnetic field with induction of 46 mT, exceeded 382 Hz.