Microscopic conditions favoring itinerant ferromagnetism

A systematic investigation of the microscopic conditions stabilizing itiner ant ferromagnetism of correlated electrons in a single-band model is presen ted. Quantitative results are obtained by quantum Monte Carlo simulations f or a model with Hubbard interaction U and direct Heisenberg exchange intera ction F within the dynamical mean-field theory. Special emphasis is placed on the investigation of (i) the distribution of spectral weight in the dens ity of states, (ii) the importance of,genuine correlations, and (iii) the s ignificance of-the direct exchange, for the stability of itinerant ferromag netism at finite temperatures. We find that already a moderately strong pea k in the density of states near the band edge suffices to stabilize ferroma gnetism at intermediate U values in a broad range of electron densities n. Correlation effects prove to be essential: Slater-Hartree-Fock results for the transition temperature are both qualitatively and quantitatively incorr ect. The nearest neighbor Heisenberg exchange does not, in general, play a decisive role. Detailed results for the magnetic phase diagram as a functio n of U, F, n, temperature T, and the asymmetry of the density of states are presented and discussed. [SO163-1829(98)08943-7].