Magnetic-stimuli rheological response of soft-magnetic manganese ferrite nanoparticle suspension

The hydrothermal fabrication of crystalline manganese ferrite (MnFe₂O₄) nanoparticles and their application as a magnetorheological (MR) fluid dispersed in an insulating oil are described herein. The morphology and crystal structure of the MnFe₂O₄ nanoparticles are revealed by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. In addition, with a relatively high saturation magnetization of the MnFe₂O₄ particles, their typical MR behavior is demonstrated by rheometric steady shear and dynamic oscillation tests under an applied magnetic field. Moreover, the flow and yield stress curves for the MnFe₂O₄ nanoparticle-based MR fluid are shown to conform to the Herschel–Bulkley model with a slope of 1.5. Finally, under the same magnetic field strength, the dynamic yield stress is shown to be higher than the elastic yield stress.