When making an electromagnet, why does a hard core stay permanently magnetized while a soft core does not?
Iron and steel are intrinsically magnetic materials, meaning that at the atomic scale they exhibit magnetic order and have magnetic poles present. Most materials, including copper and aluminum, have no such magnetic order—they are nonmagnetic all the way to the atomic scale. But while it is composed of magnetic atoms, a large piece of iron or steel normally doesn’t appear magnetic. That’s because a large piece of iron or steel contains many tiny magnetic domains. Although each of these magnetic domains is highly magnetic, with a north pole at one end and a south pole at the other end, the metal appears nonmagnetic at first because these domains point equally in all directions and their magnetizations cancel one another. Before the magnetic character of a piece of iron or steel will become visible, something must align its magnetic domains. In an electromagnet, an iron or steel core is surrounded by a coil of wire. When you run current through that coil of wire, the magnetic field of th
