Influence of magnetic field on ultrasonic propagation velocity in magnetic fluids

Experimental results for anisotropy and hysteresis of ultrasonic propagation velocity in a kerosene-based magnetic fluid are reported. The ultrasonic frequencies used are 1, 2 and 4 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0 degrees to 90 degrees. The ultrasonic propagation velocity increases with magnetic field intensity and ultrasonic frequency. Anisotropy due to the configuration of chain-like clusters is also observed. These results seem to be caused by cluster formation and the characteristic time of Brownian motion of the magnetic particles. (c) 2004 Elsevier B.V. All rights reserved.