What causes hysteresis?
Why is there a maximum saturation value of the magnetism of the magnet, and what is happening inside it to cause hysteresis? The answer is that the iron bar is made up of thousands of tiny magnets, and when the bar is unmagnetized, the magnets are pointing in all directions, so that their effects cancel each other. The magnets are the individual atoms of iron, but groups of many atoms called domains. Each atom of iron acts like a magnet, with its own north and south pole. In a domain the atoms are arranged in an orderly fashion, so that they reinforce each other. The domain acts like a magnet, but in unmagnetized soft iron the directions of magnetizations of groups of domains are so arranged that their effective magnetization is zero. The effect of the current is to swivel round the domains so that they are all pointing in the same direction. When they are all pointing in the same direction, no amount of current increase can strengthen them any more. The iron bar is magnetically satura
