Hello, I am looking to design an electromagnet with the greatest flux possible.  I am working with very limited power as well as overall volume the coil can occupy.  I am using this coil to repel a permanent magnet when pulsed.  I am currently using a Si-Fe laminated core of about .250" in length with a .100x.100 cross sectional area.  Power is DC and voltage is limited to about 5v at about 500mA.  The coil I have now uses about 400 turns.  The load I need to move is rather small ~5g.  The current setup works well but I would like to use an even smaller core if possible.  My question is what can be done to maximize the flux between the coil and the magnet.  I know reducing the gap between them will increase the force but a problem I am finding is that at low power the permanent magnet seems to overcome the relatively low output of the electromagnet and actually attract the steel core rather than repel until they are seperated to a farther distance.  Height is the dimension of concern as there is more leeway with the diameter of the coil.  Will decreasing the height and increasing the diameter lead to a stronger coil at lower power?  What effect will changing the shape or size of the core have?  Are there better core materials than Grain oriented silicon steel for use at lower power? Also is it possible to shape the core so as to concentrate the flux in a certain direction?

Thanks for any help!