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∘ to 90∘. 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.