STRONG OR WEAK FERROMAGNETISM IN TRANSITION-METALS

The various new magnetic phases obtained by epitaxial growth have regiven a large interest to the study of magnetic moment versus the lattice parameter. Considering systems with equivalent sites in the Stoner model, we propose simple criteria to obtain the energetically stablest magnetic moment as a function of the lattice parameter. Strong and weak ferromagnetism are clearly predicted. Also we point out that the well-known Stoner criterion is not enough to describe the onset of magnetism, first order transition from paramagnetic to ferromagnetic state are often present. Finally we show that, for a given "d" band occupation, the possible values for bulk fcc or bcc magnetic moment are surprisingly, rather limited.