The paramagnetism of the ferromagnetic elements

Abstract The theory of paramagnetism, originally developed by Langevin (1905) and extended by Weiss (1907) to include ferromagnetics, led to expressions giving the variation of magnetization with temperature above and below the Curie point. These proved of great value in correlating experimental results, and the general agreement between theory and experiment leaves no doubt of the essential correctness of the ideas involved. However, with the introduction of the quantum theory, the nature of the elementary carriers of magnetic moment became apparent, and new values of atomic moments were calculated from the variation of susceptibility with temperature above the Curie point. The chief problem has been to reconcile these with the values more directly measured at low temperatures. Whilst the saturation intensities of the three ferromagnetics–iron, cobalt and nickel—are known with reasonable certainty, the susceptibility measurements of several workers on iron and cobalt show such large discrepancies that, except for nickel, the theoretical development has been considerably hampered by lack of sufficiently accurate data.