A novel magnetic fluid was obtained using a colloidal dispersion of amorphous magnetic Fe-Ni-B nanoparticles into water. Its magnetorheological and viscoelastic behaviors were all investigated. Results showed that the generated particles were spherical amorphous particles 12–15 nm in diameter. The saturation magnetization of Fe-based amorphous magnetic particles could reach 49.3 emu/g. The amorphous magnetic fluid exhibited shear shinning behavior under magnetic fields and showed strong magnetic responsiveness. The yield stress increased with the rising magnetic field strength. A crossover phenomenon was observed from the modulus strain curves due to the phase transition under applied magnetic fields. The storage modulus G′ was higher than the loss modulus G″ at low strains, while G′ was lower than G″ at high strains. The crossover points shifted to higher strains with increasing magnetic field. Furthermore, G′ decreased and fell off in a power law relationship when the strain exceeded a critical value. However, G″ showed a distinct maximum at a critical strain, and then decreased in a power law fashion. The magnetorheological and viscoelastic behaviors were found to be related to the structural formation and destruction in the magnetic fluids, which is a joint effect of magnetic fields and shear flows.

Magnetorheological fluids (MRFs) based on amorphous Fe-Si-B alloy magnetic particles were prepared. The influence of annealing treatment on stability and rheological property of MRFs was investigated. The saturation magnetization ( Ms) of amorphous Fe-Si-B particles after annealing at 550°C is 131.5 emu/g, which is higher than that of amorphous Fe-Si-B particles without annealing. Moreover, the stability of MRF with annealed amorphous Fe-Si-B particles is better than that of MRF without annealed amorphous Fe-Si-B particles. Stearic acid at 3 wt% was added to the MRF2 to enhance the fluid stability to greater than 90%. In addition, the rheological properties demonstrate that the prepared amorphous particle MRF shows relatively strong magnetic responsiveness, especially when the magnetic field strength reaches 365 kA/m. As the magnetic field intensified, the yield stress increased dramatically and followed the Herschel-Bulkley model.