  In this paper, we present the study of magnetorheological properties of
magnetic fluids containing Co0.9Ni0.1 nanocluster that have been measured as a
function of both magnetic field and temperature. Co-rich nanoclusters were
synthesized by conventional homogeneous nucleation in liquid polyol.
Morphological characterization using FESEM revealed the non-aggregated nature
of nanoclusters with an average diameter of 450 nm. Crystal structure and room
temperature magnetization measurements were performed by powder XRD and
vibrating sample magnetometry (VSM). Two MR samples of different particle
volume fractions were prepared. Temperature-dependent steady shear MR
characterizations for both the samples in the range of 250C-550C demonstrated
systematic decline of MR parameters with increasing temperatures. The
temperature-induced thinning of shear stress and viscosity was explained in
terms of change in effective volume fraction and magnetic saturation. To
analyze the measured variation in MR response with increasing temperature,
suitable temperature-sensitive scaling parameters were also constructed.
Finally to generalize the trend, rheological master curves were constructed by
using time-temperature-field superposition method.
