Elemental substitution tuned magneto-elastoviscous behavior of nanoscale ferrite MFe2O4 (M = Mn, Fe, Co, Ni) based complex fluids

The present article reports the governing influence of substituting the M²⁺ site in nanoscale MFe₂O₄ spinel ferrites by different magnetic metals (Fe/Mn/Co/Ni) on magnetorheological and magneto-elastoviscous behaviors of the corresponding magnetorheological fluids (MRFs). Different doped MFe₂O₄ nanoparticles have been synthesized using the polyol-assisted hydrothermal method. Detailed steady and oscillatory shear rheology have been performed on the MRFs to determine the magneto-viscoelastic responses. The MRFs exhibit shear thinning behaviors and augmented yield characteristics under influences of magnetic fields. The steady state magnetoviscous behaviors are scaled against the governing Mason number and self-similar responses from all the MRFs have been noted. The MRFs conform to an extended Bingham plastic model under field effect. Transient magnetoviscous responses show distinct hysteresis behaviors when the MRFs are exposed to time varying magnetic fields. Oscillatory shear studies using frequency and strain amplitude sweeps exhibit predominant solid like behaviors under field environment. However, the relaxation behaviors and strain amplitude sweep tests of the MRFs reveal that while the fluids show solid-like behaviors under field effect, they cannot be termed as typical elastic fluids. Comparisons show that the MnFe₂O₄ MRFs have superior yield performances among all. However, in case of dynamic and oscillatory systems, CoFe₂O₄ MRFs have the highest caliber. The viscoelastic responses of the MRFs are noted to correspond to a three element viscoelastic model. The study may find importance in design and development strategies of nano-MRFs for different applications.