The effect of temperature on the anisotropy of ultrasound attenuation in a ferrofluid

Abstract

This paper reports results of a study on the acoustic properties of a ferrofluid, APG-513A. The anisotropy of the ultrasonic wave absorption coefficient was determined in a sample subjected to an external magnetic field. The measurements were performed in a strong magnetic field HDC = 125 kA m−1, for temperatures of 1–60°C. The dependence of the absorption coefficient of the ultrasonic wave (f = 3.6 MHz) on the angle between the direction of measurement and that of the magnetic field provided important information on the ferrofluid structure in a magnetic field. A comparison of the experimental results with the predictions of the Taketomi theory allowed a determination of the cluster radius and the number density of the colloidal particles. These data allowed us to draw conclusions about the changes in the parameters describing the structure of the ferrofluid at different temperatures. The per cent contribution of the magnetic particles in the cluster structures was estimated. On the basis of the measurements performed, it was possible to establish the proportion of the ultrasonic wave used for excitation of the translational and rotational degrees of freedom. The results revealed a significant effect of temperature on the translational and rotational components of the absorption coefficient. Moreover, the magnetic susceptibility was measured versus the external magnetic field intensity.