I am currently using a pair of cubic (5x5x5 mm) vertically alligned N52 magnets separated by 0.3 mm. My chambers are quite thin (0.19 mm from chamber surface to the tethers) and I am using MyOne C1 beads.

I am not interested in using bigger beads because they reduce the yield of the experiments.

I think that magnets with sharp edges might be useful to increase the magnetic field gradient but I have not found any company that can provide them.

Another option would be getting beads with higher saturation of magnetization. Aurosphere 800? Has someone used them for this?