The regime of strong Hubbard correlations and magnetic ground state formation in FeSi

The comprehensive study of low-temperature magnetization together with DC and AC transport has been carried out in magnetic fields up to 120 kOe in the almost magnetic narrow-gap cubic semiconductor FeSi. The analysis of the experimental data obtained on single crystals of iron monosilicide demonstrates that the Mott-Hubbard scenario of metal-insulator transition with on-site Coulomb interaction U≤3D (D is the band half-width) is likely to be the most appropriate description of the low temperature anomalies in the physical properties of this strongly correlated electron system. When the temperature decreases below 100 K, a density of states renormalization together with the formation of short-range (∼1017 cm-3) spin polarons occurs. Moreover, below Tc∼15 K a transformation of the low-density (∼1017 cm-3) heavy fermions into ferromagnetic microdomains takes place in the matrix of FeSi. The crossover in magnetic and transport properties of FeSi is discussed in terms of the many-body resonance suppression at higher temperatures T>100 K