Crossover in magnetic properties of FeSi

The magnetization of high quality iron monosilicide single crystals has been studied in a wide temperature and magnetic-field range. These data are analyzed by taking into account strong Hubbard correlations between e(g) and t(2g) states of Fe and the formation of spin polarons in the cubic FeSi matrix at low temperatures (T<100 K). These heavy particles are transformed into ferromagnetic microregions at T-c approximate to 15 K, which result in the appearance of the low-temperature anomalies in transport and thermodynamic properties of this compound. The suppression of the many-body resonance at E-F occurs in FeSi at high temperatures, thus leading to the crossover in magnetic properties of FeSi. The transition to the temperature induced magnetic moments causes a dramatic increase of the magnetic susceptibility at temperatures T> 100 K.