Dynamics of concentration profiles of nano-sized magnetic particles in a non-uniform magnetic field

Results of numerical and experimental investigation of nano-sized magnetic particles diffusion in a non-uniform magnetic field are presented. Diffusion of the nanoparticles is studied in a 2D Hele-Shaw cell submitted to a magnetic field gradient along the vertical axis. An optical interferometry method (particularly, Mach-Zehnder interferometer) is applied to read the concentration profile by proceeding the time. Experiments confirm the theoretical prediction of a "negative region" of the concentration profile in the middle of the Hele-Shaw cell, i.e. dφ/dH <0. The concentration profile is calculated numerically from the conservation equation and compared with the experimental results and with the analytical solution in the boundary layer approximation.