Correlation effects in ferromagnetism of transition metals

The effect of electronic correlations on the ferromagnetic instabilities, effective local moments, and fluctuations in spin and charge in a transition metal is discussed with a model Hamiltonian which includes intraatomic Coulomb and exchange interactions. The one-particle properties of $d$ electrons are described by bcc and fcc canonical bands. We find that reduction of density fluctuations and formation of local moments change the Stoner criterion and the condition for the ground state to be completely ferromagnetic. The magnetic states of Fe, Co, and Ni are studied in more detail, where the electrons are found to be considerably correlated for realistic model parameters. Redistribution of electrons between the $e_g$ and $t_{2g}$ states seen there causes deviations from the Stoner theory and is responsible for different exchange splittings of both types of states. The results are in qualitative agreement with the experimental data and suggest the use of anisotropic exchange correlation potentials in transition metals.