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The research work examines the influence of magnetic field and temperature on the magneto viscous and magneto viscoelastic nature of cobalt ferrite ferrofluid (FF). Steady rotational and oscillatory rheological measurements which examined the rheological responses of the fluid have been performed. A steady state flow was established through the application of suitable relaxation modulus and attempt was made to regulate unwanted oscillatory behavior by application of damping function. The particles were ultra-sonicated and coated with oleic acid to minimize agglomeration and improve fluid stability and its rheological behavior. The fluid is underdamped at high shear rate and high magnetic field due to damping factor that is less than one but overdamped behavior was obtained at low shear rate. Storage modulus (G’) and loss modulus were used to examine the viscoelastic behavior of the fluid. This fluid is accurately viscoelastic, because it exhibits of both elastic and viscous behaviors. Storage modulus is higher than loss modulus as a result of dominant magnetostatic forces at low strain rate. A crossover point was formed at critical strain due to overlapping of loss and storage modulus curves at high strain rate, this effect indicates the formation of phase transition. This occurred due to dominant hydrodynamic forces over magnetostatic forces. Magnetic effect revealed a steady increase in viscous effect which is as a result of formation of enhanced chain-like structure and strong particle aggregation. Enhanced viscous effect was shown in the presence of low temperature, low angular frequency and high applied magnetic field.

Cadmium nickel (Cd-Ni) ferrite samples have been successfully synthesized via chemical co-precipitation technique. The structural analysis revealed the formation of FCC framework and Fe-phase in a trivalent state. The crystallite size is decreased with increasing Cd2+ ion composition whereas the lattice constant is increased. SEM was used to obtain the surface morphology and average grain size of the microstructure. The FTIR shows the formation of metal oxide, hydroxyl and carboxylic groups. EDX revealed the formation of Ni2+, Cd2+, Fe3+, and O2- ions in proper stoichiometric composition. Large optical losses were revealed by Cd2+ poor-NiFe2O4 samples whereas Cd2+ rich-CdxNi1-xFe2O4 samples revealed low optical losses and showed enhanced photoconductivity and photoelectric effect. Result from optical analysis showed that Cd2+ rich-CdxNi1-xFe2O4 nanoparticles can be used as infrared (IR) detector, ultraviolet (UV) filter and in optoelectronics device applications. VSM measurement showed an increase in saturation magnetization and decrease in coercivity as Cd2+ ion content is increased. The remanance magnetization and magnetic anisotropy were also examined. Photoluminescence (PL) spectroscopy examined the nature of the light emission of the samples at the excitation wavelength 380 nm and emission of series of colours such as red, green, yellow, orange and violet light at different wavelengths were found.