M. Łabowski

The influence of the concentration of ferroparticles in a ferrofluid on its magnetic and acoustic properties

This paper reports results of a study of magnetic and acoustic properties of a ferrofluid, EMG-605. The measurements were performed for three samples of the same ferrofluid differing in concentration. The magnetic susceptibility was measured as a function of an external magnetic field for each sample, which allowed us to determine the magnetization curves and saturation magnetization. The results provide information on the mean magnetic moment and the mean radius of the magnetite grain. In the samples subjected to an external magnetic field, the anisotropy of the ultrasonic wave absorption coefficient was determined. The mechanisms of ultrasonic wave energy dissipation through the translational and rotational degrees of freedom were established for some ferrofluid concentrations.

Hysteresis of changes of ultrasonic wave absorption coefficient in a magnetic fluid caused by the magnetic field

The magnetic fluids change their structure under the influence of an external magnetic field and do not return to the initial state after the magnetic field removal. It is supposed that the cluster formed in the fluid subjected to a magnetic field remains after the field has been removed. The resulting dependence of the ferrofluid properties on its magnetic history has been studied by the analysis of changes in the ultrasonic wave absorption coefficient.

Resonance absorption of the ultrasonic waves in magnetic liquids in DC magnetic field

An external magnetic field, applied to a magnetic fluid, gives rise to spherical and chain-like clusters. The present paper is based on an acoustic method permitting the determination of the presence and size of the clusters by having recourse to resonance absorption of an ultrasonic wave in a magnetic fluid acted on by a magnetic field. We report our measurements of the variations Δα of the ultrasonic absorption coefficient for three frequencies of the wave in a selected magnetic fluid versus the external magnetic field strength applying the pulse method.

The measurements of anisotropy of ultrasound propagation and magnetic susceptibility in viscous ferrofluid

Results of experimental study of anisotropy of ultrasound propagation and anisotropy of magnetic susceptibility in a ferrofluid of considerable viscosity are reported. The dependence of the propagation velocity and absorption coefficient of ultrasonic wave on the angle between the direction of measurement and that of the magnetic field provides important information on the ferrofluid structure in a magnetic field. The results show that the ultrasonic absorption coefficient of a wave propagating in a viscous ferrofluid in a DC magnetic field depends mainly on the rotational degree of freedom. Measurements of the anisotropy of the magnetic susceptibility of a ferrofluid bring the information on the magnetic moment of the magnetic particles and their mean radius.

Effects of the sweep rate of the magnetic field on the changes of ultrasonic wave velocity in magnetic fluid

An external magnetic field applied to a homogeneous magnetic fluid induces a change in its structure manifested as the appearance of chains of magnetic particles arranged along the direction of the field. This change implies changes in the acoustic and magnetic properties of the magnetic fluid such as the acoustic wave propagation velocity and coefficient of ultrasonic wave absorption, and in magnetisation. The paper reports results of a study on the influence of the magnetic field sweep rate and the magnetic fluid temperature on the value of ultrasonic wave velocity, proving that the degree of the aggregation of the magnetic particles (chain formation process) depends on the above-mentioned parameters.