Iron oxide ionic ferrofluid (FF) was synthesized via co-precipitation method. X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM) were used for characterization of the solid particles, and the rheological properties of FF at relatively low shear rates were investigated with a special rheometer with variable magnetic field. Iron oxide particles were superparamagnetic with mean particle size of 10nm. Rheological results show that the shear thinning behavior in the absence and presence of magnetic field is different from that based fluid behavior and also concentration of FF can affect its rheological properties. Moreover, contrary to expectation, the magnetoviscous effect showed an initial increase at low shear rates in absence of magnetic field and an increase-decrease-increase behavior with magnetic field.

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