Unified treatment of theory on magnetic properties of FeGe and FeSi

The magnetic properties of FeGe and FeSi are studied in a unified way on the basis of the realistic model derived from the first principle calculations. We can show that, with decreasing the temperature, the transition from the paramagnetic metallic state to the ferromagnetic metallic state takes place for FeGe, while the transition of FeSi from the paramagnetic metal to the paramagnetic insulator is a continuous crossover, consistent with experiments. It is shown that the distinct magnetic behaviors in FeGe and FeSi are attributed to the difference of the strength of the electron correlation effects, controlled by the effective bandwidth.