Field-induced magnetorheological study towards the active magneto-viscoelastic behavior of stable MnFe 2 O 4 magnetic nanofluid

This work presents the fine-tuned synthesis of MnFe 2 O 4 oleic acid-coated magnetic nanoparticles (MNPs) by the chemical co-precipitation method. The X-ray photoelectron spectroscopy (XPS) was utilized to investigate the elemental composition and oxidation state of oleic acid-coated MnFe 2 O 4 MNPs. The Fourier transform infrared spectroscopy (FTIR) spectra were used to confirm the functional groups in the oleic acid-coated MnFe 2 O 4 magnetic nanoparticles. The spherical shape of MnFe 2 O 4 MNPs is confirmed by Field emission scanning electron microscopy (FESEM) and High-resolution transmission electron microscopy (HRTEM) techniques. Zeta potential (ζ) measurements were performed to confirm the stability of MnFe 2 O 4 magnetic nanofluid (MNF). Magnetic measurements (M−vs−H) reveal the saturation magnetization, M s  = 20.3 emu/g and coercivity, H C  = 30 Oe, confirming the single domain superparamagnetic nature at 300 K. Field-induced shear thinning behavior of the MnFe 2 O 4 magnetic fluid is confirmed by a power law, η = c γn  +  n∞ and steady-state behavior measurements. Magneto viscous effect initially increased at a low shear rate of 20 s −1 and then decreased at a higher shear rate of 100 s −1, which confirms the stability of the MnFe 2 O 4 magnetic fluid. Also, the highest deflection angle, θ = 243 m.rad of MnFe 2 O 4 magnetic fluid was observed at a moderate shear rate 100 s −1 and a high magnetic field of 1.2 T, while the lowest value of deflection angle, θ = 65 m.rad was observed in the absence of magnetic field. In contrast, the storage modulus (G') is greater than the loss modulus (G''), in corroboration with the viscoelastic-to-viscous behavior of MnFe 2 O 4 magnetic fluid.