LAUSR

Abstract Water-based magnetite nanofluids of various Zn-doping concentrations have been synthesized through co-precipitation method. The structural and morphological studies are done using X-Ray Diffraction and Transmission Electron Microscopy technique. Magnetic studies reveal that, all the samples possess superparamagnetic nature and the sample with dopant concentration x = 0.2 shows maximum magnetization. Also, the particle size distribution is calculated for all the samples from M-H curves by fitting with Langevin function and is found to be in agreement with the values calculated from XRD and TEM. The Ultrasonic velocity studies shows that the sample with doping concentration x = 0.2 shows higher inter-particle interaction. The measured ultrasonic velocity values of the undoped magnetite nanofluids at various temperatures are found to fit in the Urick model. Acoustical parameters such as adiabatic compressibility, acoustic impedance, mean-free path, Rao's constant and Wada constant are derived and analysed, which again confirms the maximum interparticle interaction shown by Zn0.2Fe1.8O4 sample. The temperature effect on acoustical parameters is explained with open and closed packed structure of water. Also, the acoustical studies are made by applying various magnetic fields and the changes observed are attributed to the formation of clusters in the samples. In addition to that, the attenuation coefficient of ultrasonic wave propagating through all the samples is measured with and without applying magnetic field and is compared with value obtained using stoke's theory.