Two-band model for the magnetism of iron

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Abstract
We introduce a two-band model for the magnetism of Fe and report results in fairly good agreement with many experimental facts both at low and high temperatures. One band is narrow and degenerate, representing the ‘‘quasilocalized’’ electrons. The second one is a wide band containing very few itinerant electrons. The occupation of these bands is suggested by positron annihilation data and the observed saturation moment. The one-particle excitations and the transverse dynamical susceptibility are calculated within the Hartree-Fock and the random-phase approximations, respectively. An exchange coupling between electrons of both bands plays a crucial role in determining the magnetic state of the system, as evidenced in the derived modified Stoner criterion. On the other hand, an effective interatomic exchange coupling between electrons of the narrow band is necessary for the spin-wave stiffness constant to assume the extrapolated ‘‘experimental value’’ at zero temperature. Moreover, an excellent fitting of the temperature dependence of the static paramagnetic susceptibility is obtained. The results are analyzed in view of Stearns’s ideas concerning the origin of the magnetism of Fe.

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