Comparison of the Change of Acoustic Attenuation and Anisotropy in Magnetic Fluids Based on Transformer Oils

In the application of a magnetic field to a magnetic fluid, magnetic nanoparticles are created with various structures. In this contribution, we compare the structural changes in three types of transformer oil-based (TECH-NOL, MOGUL, and MOL) magnetic fluids upon different developments of magnetic fields and temperatures by the acoustic spectroscopy. The change of the acoustic attenuation was slow (> 10 min) or fast (< 4 min) depending on the step change of the magnetic field. After switching off the magnetic field, a fast decrease of the acoustic attenuation was observed only for MOL-based magnetic fluid. For linear changes of the magnetic field, the acoustic attenuation increased in steps and a hysteresis effect was observed. The effect of anisotropy of the acoustic attenuation was observed and analysed.