Synthesis, Structure and Magnetic Properties of Cobalt-Zinc Nanoferrite for Magnetorheological Liquids

Abstract

An upcoming trend in the application of micro- and nanosized magnetic particles is the development of magnetorheological fl uids for the automatic systems of damping devices in which the particles play the role of a component in the complex dispersed phase. In the search for magnetic materials for agnetorheological fl uids, the most important criteria in choosing are high shear stress of the suspension based on the particles vs. applied magnetic fi eld and a low value of coercive force. The aim of the work was to investigate the structure, morphology, and magnetic properties of the nanoscaled powders of Co, Zn-ferrites and the evaluation of their effectiveness upon the rheological properties of the developed magnetorheological fl uids. The Co, Zn-ferrite nanopowderwas synthesized by spray-drying technique followed by heat treatment in the presence of the inert matrix. The features of its morphology were investigated by x-ray diffraction analysis, transmission electron microscopy, and IR-spectroscopy. The powdered nanoferriteCo0.65Zn0.35Fe2O4, used as a fi ller of magnetic fl uids, demonstrated values of coercive force Hc (10K) = 10.8 kOe, Hc (300 K) = 0.4 kOe as well as relative residual magnetization Mr/Ms(10K) = 0.75, Mr/Ms(300K) = 0.24. The proposed synthesis technique allows obtaining crystallized particles of the ferrite with sizes not larger than 50 nm, which possess high shear stress in magnetorheological suspensions. The synthesis technique allows controlling the magnetic properties of Co,Zn-ferrite (as a component of magnetorheological suspensions) by non-magnetic double-charged ion substitution of Co2+, i.e. ions Zn2+, in Co,Zn-spinel has been developed. The possibility has been established to decrease the coercive force and increase the magnetization up to the maximum cobalt content, corresponding to the composition formulae Co0.65Zn0.35Fe2O4. The high value of shear stress (103 Pa) at a relatively low value of magnetic induction (600 mT and higher) makes the material applicable as a filler for the magnetorheological suspensions of damping devices.