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

Abstract

We report proton-nuclear magnetic resonance experiments on a diluted water solvent magnetic fluid of colloidal volume fraction φ=0.30%. By sweeping the external magnetic field strength, H0, applied to the magnetic fluid around 4000 Oe, we found one major resonant field, HM, and two satellite resonant fields, HS1 and HS2, which correspond to resonant protons in three different coexisting phases. HS1 corresponds to needle-like macroclusters, or a dense phase, in which φ is evaluated to be 0.66% from HS1, while HS2 corresponds to needle-like stripes, or a diluted phase, in which φ is evaluated to be 0.24%. HM corresponds to the rest of the area, the major region. The local field which the proton felt consisted of H0, 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 H0. The discovery of the three coexisting phases is not explained by the conventional two phase separation model.