  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.
