Temperature dependent acoustic properties of temperature sensitive magnetic fluid subjected to magnetic field

Abstract

The ultrasonic velocity of temperature sensitive magnetic fluid is investigated as a function of volume fraction, temperature and magnetic field. The ultrasonic velocity decreases with increasing volume fraction of magnetic nanoparticles. This is attributed to the particle-carrier interaction which leads to form shorter aggregates. The pre-aggregates in magnetic fluid break when temperature increases in the absence of a field. Magnetic field makes the system anisotropic to ultrasound wave propagation. The change in ultrasonic propagation velocity under the influence of magnetic field shows chain like alignment for low volume fraction of magnetic nanoparticles (1.6%) which changes to short dipolar chains at an intermediate volume fraction (6.8%). Above this volume fraction, short chains become thicker by aligning sidewise to the neighboring chains resulting in spherical drop like structures. The modified Tarapov's theory fit to change in ultrasonic propagation velocity confirms the transformation from chains to aggregates with increasing magnetic nanoparticles volume fraction. The optical microscopy study also confirms the results. Upon increasing the temperature the field dependent velocity variation shows breaking of thick chain like aggregates. The modified Tarapov's theory fit shows that this is attributed to decrease in magnetic moment with increasing temperature. The variation of magnetic moment with temperature obtained from the fitting gives the Curie temperature of fluid as 363K. This value agrees with those obtained from other techniques.