DYNAMICS OF A FERROFLUID IN CONTACT WITH Co MICRO-SQUARE ARRAYS

The square arrays are fabricated by e-beam lithography on polycrystalline Co sputtered on glass substrates. First, a continuous layer, 1000 nm thick, of polycrystalline Co is grown. This thickness guarantees optical opacity for the light used in the experiments, a 632.8 nm wavelength 1.5 mW laser. Secondly, the continuous Co layer is locally etched (all the way through to the glass substrate) to form an array of 5 x 5 μm Co squares separated by 0.5 μm using ion milling technique. The ferrofluid used is formed by spherical cobalt ferrite (CoFe2O4) nanoparticles (average diameter 12.3 nm) stabilised in water. We use a volume fraction of 7.84 %.