Effect of Magnetic Susceptibility Gradient on the Magnetomigration of Rare-Earth Ions

Magnetomigration of rare-earth ions activated by thermal and evaporation-based gradients was demonstrated using Mach-Zehnder interferometry. Magnetic susceptibility gradients were induced in aqueous solutions of rare-earth ions by local heating/cooling or by evaporation of the solvent. Both methods yielded the enrichment of strongly paramagnetic Dy3+ ions in the region of the highest magnetic field. Three different orientations of the magnetic field were tested using temperature as the source of magnetic susceptibility gradient. Enhanced magnetomigration was observed when gradients of magnetic field and magnetic susceptibility were noncollinear, indicating that the rotational component of the magnetic force drives the process. Additionally, four rare-earth ions with distinct values of magnetic susceptibility were studied: the diamagnetic ion Y3+ and the paramagnetic ions Nd3+, Gd3+, and Dy3+. A strong correlation between the obtained magnetomigration and the magnetic susceptibility of the rare-earth ions was found. When heating/cooling or evaporation were stopped during magnetization experiments, the magnetic effect gradually faded. This demonstrates that the presence of magnetic susceptibility gradients in the system is crucial for the magnetomigration. These findings are of importance for the development of a magnetic separation process for rare-earth ions.