Proton-nuclear magnetic resonance study of water solvent magnetic fluid's phase separation

We report proton-nuclear magnetic resonance experiments on a diluted water solvent magnetic fluid of colloidal volume fraction phi=0.30%. By sweeping the external magnetic field strength, H-0, applied to the magnetic fluid around 4000 Oe, we found one major resonant field, H-M, and two satellite resonant fields, H-S1 and H-S2, which correspond to resonant protons in three different coexisting phases. H-S1 corresponds to needle-like macroclusters, or a dense phase, in which phi is evaluated to be 0.66% from H-S1, while H-S2 corresponds to needle-like stripes, or a diluted phase, in which phi is evaluated to be 0.24%. H-M corresponds to the rest of the area, the major region. The local field which the proton felt consisted of H-0, the Lorentz field and the demagnetizing field. Accordingly, in the major region, the extra field of about 2 Oe in the inverse direction was applied to the protons in addition to H-0. The discovery of the three coexisting phases is not explained by the conventional two phase separation model. (C) 2000 American Institute of Physics. [S0021-8979(00)29308-0].