The contribution of the magnetization to the after-effect in iron

Abstract

In recent experiments on the after-effect of the magnetostriction in α-iron due to the diffusion of interstitial carbon or nitrogen, it was observed that the magnetic contribution to the after-effect is opposite in sign to the mechanical contribution. It was also found that the magnetic contribution to the free energy, D, differs more radically between carbon and nitrogen than the mechanical contribution, ϵ. We show that the energy D is related to changes of the second rank component of the electrostatic interaction energy of the interstitial impurity with the iron atoms. These are caused by distortions of the 3 d electron clouds of the iron atoms by the magnetization. By also relating the energy ϵ to changes of the zero-th rank component of the electrostatic interaction energy, caused by anisotropic magnetostrictive strains, we are able to understand why the energy ϵ for carbon and nitrogen is proportional to their ionic radii whereas the energy D differs more radically. The opposite signs of the energies D and ϵ, imply that the magnetization, through spin-orbit interaction energy of the 3 d iron electrons, favors states with prolate charge distributions over those with oblate charge distributions.