Effects of pd-hybridization in strongly correlated insulator FeSi

•Strongly correlated compound FeSi investigated in the pd-hybridization model.•Transfer states between p- and d-bands induces spin fluctuations in the insulator phase.•Increasing spin fluctuation amplitude leads to the disappearance of hybridization gap.•Spin susceptibility induced by fluctuations with increasing temperature.•The result of the calculation of the susceptibility agrees with experiment.

We study the hybridization effects in the system of the strongly correlated d-electrons and the nearly free p-electrons. It has been established that there is the hybridization of the spin states of electrons in addition to the hybridization of p- and d-states of different atoms. This leads to the formation of four energy bands – spin-symmetrized and spin-antisymmetrized of singlets of A- and B-states. It has been shown that the increase of the temperature leads to a change of the number of d-like states, gaps into hybridization spectra of spin-antisymmetrized and spin-symmetrized states, and to the shift of these spectra relative to each other. Numerical analysis performed on an example of strongly correlated semiconductor iron monosilicide. The semi-quantitative description of the electronic and magnetic properties of this compound has been obtained. In particular, we obtained the disappearance of the semiconducting gap at 90 K and the values of temperatures corresponding to the features of the temperature dependence of the magnetic susceptibility.