Dynamics of magnetic nano-flake vortices in Newtonian fluids

TL;DR

This paper investigates the rotational dynamics of ferromagnetic nano-flake discs in Newtonian fluids, combining analytical modeling with experimental validation to understand their behavior under magnetic fields and Brownian motion.

Contribution

It provides a comprehensive analytical model for nano-flake vortex dynamics in fluids, validated by experiments, and estimates orientation uncertainty due to Brownian torque.

Findings

Excellent agreement between model and experiments.

Orientation uncertainty proportional to thermal and magnetic energy ratio.

Potential applications in biotechnology and fluidics.

Abstract

We study the rotational motion of nano-flake ferromagnetic discs suspended in a Newtonian fluid, as a potential material owing the vortex-like magnetic configuration. Using analytical expressions for hydrodynamic, magnetic and Brownian torques, the stochastic angular momentum equation is determined in the dilute limit conditions under applied magnetic field. Results are compared against experimental ones and excellent agreement is observed. We also estimate the uncertainty in the orientation of the discs due to the Brownian torque when an external magnetic field aligns them. Interestingly, this uncertainty is roughly proportional to the ratio of thermal energy of fluid to the magnetic energy stored in the discs. Our approach can be implemented in many practical applications including biotechnology and multi-functional fluidics.