Proton nuclear magnetic resonance and optical microscopic studies of magnetic fluids

Proton nuclear magnetic resonance has been studied for H-1 in the solvent o f super-paramagnetic fluid in which fine particles of magnetite, Fe3O4, are suspended as colloid. An optical microscope has been used to observe the f ilamentary agglomeration of colloidal clusters under an applied magnetic fi eld, H-0. The filaments are aligned in the direction parallel to H-0 within a minute after the application of the magnetic field of 1 kOe. An average of local magnetic fields at the positions of H-1 is antiparallel to the dir ection of H-0, and its magnitude depends on the arrangements of filaments. A tentative estimate of the interacting force between a colloidal cluster a nd a filament has been done by the measurement of the growing velocity of f ilaments. The force is estimated to be an order of 10(-19) dyne (10(-24) N) under H-0 of 1.1 kOe.