what is the best type of metal to use for a rod core for a large electromagnet?

Question

steel? iron? something else?

Answer 1

Well, the canonical answer would be "soft iron" -- a low-carbon steel alloy especially chosen to magnetise easily and lose any acquired magnetism quickly. There are also various iron-based ceramic materials (ferrites) which can be used as cores. But unless you have access to a specialist supplier, you may well be stuck with a limited range. The best thing to use if nothing else is available is ordinary mild steel. Annealing (heating it to a dull cherry red and allowing it to cool as slowly as possible) might improve its performance a little (and will certainly look good in any project write-up).

If you're using DC to energise your electromagnet, the core can be a simple steel rod.

If you're using AC (yes, this does work: an unmagnetised piece of steel will be attracted equally strongly to a North or South pole, and won't have moved out of the way in the time it takes for the mains to reverse direction) then your core needs to be non-conductive across its width, to avoid power losses due to eddy currents. You could use a bundle of plastic-coated (or heavily painted) steel wires, or a stack of painted sheets of thin steel (like transformer stampings). But, diodes are cheap nowadays, so you might find it simpler to use a bridge rectifier and a solid core.

Best of luck with it!

Answer 2

materials with high permeability.
iron has 5000, steel has 800, but nickel-iron alloy has the highest permeability.

Answer 3

heavy metal