Magnetic Fields Enrich Paramagnetic Ion Concentrations via Magnetophoresis and Magnet-Induced Convection

Magnetic fields alter the transport behavior of paramagnetic solutions, with implications for the processing and separation of critical materials. We monitored the diffusion of rare-earth metal ions across a gel medium in the presence of a 0.5 T magnet and observed a 6-14% increase in effective diffusivity of paramagnetic Nd³⁺ and Dy³⁺ ions in 0.3-0.7 M solutions, with no appreciable effect on diamagnetic La³⁺ ions. This magnetophoretic enhancement was larger in the presence of nitrate compared to chloride counterions. Continuum fluid dynamics simulations based on the magnetic Kelvin force suggested characteristic migrating domain sizes of 7.7-51.7 nm. Furthermore, the direct addition of a droplet of paramagnetic ion solution onto a thin layer of water produced patterns of local ion enrichment within a few seconds, rather than hours, indicating an even stronger effect arising from magnetically induced convection. These results demonstrate how magnetic fields facilitate the enrichment of critical material ions in solutions.