I'm attempting to build an alternating current electromagnetic coil and want to maximize its potential field. My initial query was to find the very best core material for the electromagnet. I found an older post (2005) on the subject and saw some very interesting answers there. Being new here I learned that we can not ask new questions on old posts so I'm presenting these questions here. Thank you for any responses. What are the benefits/downfalls of using a permanent magnet as the core of an electromagnet? (like a series of round Neodymium magnets - stacked in opposing faces - n/s,s/n/n/s, etc) Will the electromagnet (with a magnet core stacked in the opposing nature as above) change polarity when the current through its coil changes polarity? I know that using a ferrite core will allow the polarity change but am not sure about the magnet core. A poster named Intuitive said that he had made several magnets from joining broken bits of old magnets in that opposing fashion, with n/s, s/n, n/s, s/n, etc. I'm not sure if he was implying that he was physically joining these opposing faces together with some sort of cement or something. Is it possible to physically join magnets together with some sort of bonding agent? Also (and this is just for curiosity's sake) he said that certain magnets need to be packaged in a special way when being shipped because they can actually wipe out credit card info and hard drive data info at up to 5 feet away. I did not know any material existed that could insulate magnetic fields. Was I wrong about that? And if so, what is the material and is it possible to use that insulating material to concentrate a magnetic field or flux?