Ferrite particles and rare earth magnets can have plenty of force between them. That is easy to see if you have a ferromagnetic fluid full of microscopic ferrite; a magnet will make it distort. There are a number of videos out there showing that. Iron in blood is quite different magnetically because the electrons are bound differently. Anyway, I have a vial of ferromagnetic fluid and a strong magnet easily sticks to even small drops of it.