STUDY OF STRUCTURAL CHANGES IN WATER-BASED MAGNETIC-FLUID BY ACOUSTIC SPECTROSCOPY

Changes in the structural arrangement of magnetic nanoparticles in water-based magnetic fluid under the effect of an external magnetic field were studied by the methods of acoustic spectroscopy. The interaction between the magnetic field and the magnetic moment of nanoparticles leads to the aggregation of magnetic nanoparticles to various structures followed by the increase of acoustic attenuation. The changes of attenuation of acoustic waves at the application of linear increase / decrease and jump changes of the magnetic field at various temperatures were measured. The main part of the article is focused on the description of anisotropy of acoustic attenuation and the determination of structure types of nanoparticles created in magnetic fluid. Acoustic attenuation decreased monotonically with increasing angle between the vector of the acoustic wave and the direction of the magnetic flux density, supporting mainly chains or smaller structures in the study. The measured anisotropy of acoustic attenuation using three different models was analyzed. By comparison of experimental anisotropy measurements with theoretical predictions models, a prolate ellipsoid as the most probable structure was determined.