Structure of transformer oil-based magnetic fluids studied using acoustic spectroscopy

The structural changes in transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. The attenuation of acoustic wave was measured as a function of the magnetic field in the range of 0–300mT and in the temperature range of 15–35°C for various magnetic nanoparticles concentrations. The effect of anisotropy of the acoustic attenuation was determined, too. The both strong influence of the magnetic field on the acoustic attenuation and its hysteresis were observed. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs, leading to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids also has very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. The observed influences of both magnetic field and temperature on the investigated magnetic fluid structure are discussed.