The heat transfer oil-based magnetorheological fluid （MRF） was prepared using oleic acid-modified micron carbonyl iron powder as a magnetic dispersed phase and strontium hexaferrite （SrFe12019） nanoparticles as an additive. The sedimentation stability of MRFs was studied. The results indicated that the stability of MRFs was improved remarkably by adding SrFel2019 nanoparticles and the sedimenta- tion ratio was only 0.88 in 20 days when the content of nanoparticles reached 10wt%. The rheological properties were characterized by a HAAKE rheometer without a magnetic field and a capillary rheometer with and without a magnetic field. The effects of SrFe12019 nanoparticles, the temperature, and magnetic field strength were investigated. In addition, the rheological properties could be predicted well using the improved Herschel-Bulkley model, even under a magnetic field. A theoretical model was also proposed to predict the yield stress based on the microstructure of the MRF under an applied magnetic field.
