The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid

• Published in: Journal of magnetism and magnetic materials 2017-06, Vol.431, p.74-78
• Main Authors: Parekh, Kinnari, Upadhyay, R.V.
• Format: Article
• Language: English
• Subjects: Acoustic impedance; Acoustic velocity; Aggregates; Alignment; Anisotropy; Chains; Clusters; Dipolar interaction; Elastic properties; Elongation; Magnetic effects; Magnetic fields; Magnetic fluid; Magnetic moments; Magnetism; Propagation; Ultrasonic wave propagation; Velocity anisotropy; Wave propagation
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2016.08.024

Ultrasonic wave propagation in the aqueous magnetic fluid is investigated for different particle concentrations. The sound velocity decreases while acoustic impedance increases with increasing concentrations. The velocity anisotropy is observed upon application of magnetic field. The velocity anisotropy fits with Tarapov’s theory suggests the presence of aggregates in the system. We report that these aggregates are thermodynamically unstable and the length of aggregate changes continuously with increasing concentration and, or magnetic field and resulted in a decrease in effective magnetic moment. The Taketomi's theory fits well with the experimental data suggesting that the particle clusters are aligned in the direction of the magnetic field. The radius of cluster found to increase with increasing concentration, and then decreases whereas the elastic force constant increases and then becomes constant. The increase in cluster radius indicates elongation of aggregate length due to tip-to-tip interaction of aggregates whereas for higher concentration, the lateral alignment is more favorable than tip-to-tip alignment of aggregates which reduces the cluster radius making elastic force constant to raise. Optical images show that the chains are fluctuating and confirming the lateral alignment of chains at higher fields. •Magnetic field induced aggregates investigated using ultrasonic wave in aqueous magnetic fluid.•Velocity anisotropy induces upon applications of magnetic field.•Tarapov’s theory fit shows reduction in effective magnetic moment as concentration increases.•Taketomi's theory shows alignment of clusters in field direction.•Cluster radius increases and then decreases with increasing volume fractions.•Optical images show that fluctuating chains and lateral alignment of chains at higher fields.