SPIN FLUCTUATIONS AND ELECTRONIC SEMICONDUCTOR-METAL TRANSITIONS IN IRON MONOSILICIDE

This paper discusses the effect of dynamic zero-point and thermal spin -density fluctuations (SDF) on the electronic spectrum of the nearly-f erromagnetic semiconductor FeSi. It is shown that near T=0 degrees zer o-point SDF can lead to so much splitting of the electron states of th e valence and conduction band that a ''gapless'' ground state arises. As the temperature increases, the forbidden gap in the spectrum of d e lectrons first reappears due to suppression of zero-point fluctuations and then disappears again, as the amplitude of thermal spin fluctuati ons increases. It is these transformations of the electronic spectrum that are the reason for the anomalous changes in the magnetic suscepti bility with temperature observed experimentally. (C) 1998 American Ins titute of Physics. [S1063-7834(98)01108-3].