How pointed can magnetized ferrofluid tips be

The typical magnetized ferrofluid tip radius is ~0.1 mm, where capillary stress balances magnetostatic stress. Here we confirm experimentally the controlling role of magnetic saturation in more general conditions, even for ferrofluid menisci in highly nonuniform magnetic fields created by supporting them at a ferrous needle tip facing a strong magnet. We use a wide range of ferrofluid tensions and solvent polarities. Substantial changes in saturation magnetization are achieved with solvent evaporation, and record tip radii to 9.5 mm demonstrated at high volume fractions of magnetic particles.