Conduction electron self‐energy effects in ferromagnetic semiconductors

Abstract

AbstractThe interaction between conduction electrons and localized lattice spins is studied. The problem is considered in broad conduction band ferromagnetic semiconductors at low temperatures using spin‐wave approximation to obtain the lattice moment correlation functions. Calculating the self‐ energies in generalized Born approximation for both the conduction electron spin directions it is shown that a spin gap does not exist i.e. even at zero temperature the spin down band has a tail extending down to the spin up band edge. Consequently the relative conduction electron spin polarization does not reach the ideal value 100%, but ‐ with parameter values appropriate for EuS ‐ remains always smaller than 93% and further keeps practically constant at low temperatures. At T = 10 K the value 93% exactly coincides with the known experimental result for EuS. In addition the mobility including self‐energy terms only is evaluated. For spin down electrons the mobility is found to be several orders of magnitude smaller than for spin up electrons. Moreover, due to the non‐existence of the spin gap the spin flip scattering is always present, which tends to reduce the mobility of spin up electrons from the ordinary Boltzmann result.