Creating a Perma Magnetic Field Around a 1mm Glas Ring

Does anyone have experience or a supplier contact that can offer a type of magnetic coating (perhaps nano particles)onto the outer edges of a 1mm round glas ring?

Are there companys or organisations that can provide and place sustainable magnetic particels in very precise dimesions / perhaps defined multiy layers and width position onto such a small glas edge?

We have done some experiments with fero magnetic materials. But they get to big and can not be placed precise enough. We have no real sense on the magnetic field density needed so we need to produce several different prototypes to be tested.

thanks for any tip