Looking for a way to increase magnetic forces in electrical devices, an option is reduce the air gap, but some times it is not a practicable solution. The question is what happend if we put a ferrofluid between the magnets? Imagine the following situation: a closed volume composed by a non magnetic tube and two magnets in N-S orientation at the ends. First case, air between magnets. Second case, ferrofluid filling the gap. Is the force in the second case bigger that force in first case? The ferrofluid has more magnetic permeability, but my doubt is about pressure gradients inside the fluid . I do not know if the pressure is constant along the tube or we have a higher pressure at the ends. If it is the case, do it balance the increment in force due to a higher magnetic permeability in the medium? I did not make the experiment. What do think about that? please remember that a ferrofluid has magnetic particles inside, and it experiment forces due to magnetic fields.