Energy relations in hard and soft magnetic materials

Koch has criticized the common assumption that the force exerted by a permanent magnet on a keeper can be calculated from the increase of the internal or external energy of the magnet, since both these quantities pass through a maximum as the keeper is removed. He introduces a new term the "Demagnetizing energy". The present paper shows that this term is equal to the total field energy inside and outside the magnet, the former being equal to the energy of the self-demagnetizing field with the magnet treated as free space. The energy transitions in a permanent magnet are more easily understood, if it is recognized that the energy at the remanence point on closed circuit is not zero. This energy appears to be used in D.C. pulse transformers and ferrite memory cores.