Ground state formation in a strong Hubbard correlation regime in iron monosilicide

Low-temperature anomalies in the physical properties of iron monosilicide are analyzed based on the results of thorough measurements of the conductivity, Hall coefficients, thermo emf, and magnetic characteristics of high-quality single-crystal FeSi samples at liquid helium (LHe) and intermediate temperatures. It is demonstrated that the most adequate and consistent interpretation of the experimental magnetic, transport, and optical characteristics can be given within the framework of the Hubbard model. The model parameters are determined and the arguments are presented which provide evidence of the spin polaron formation and the density of state (DOS) renormalization taking place in FeSi in the vicinity of the Fermi energy at intermediate temperatures. It was found that a decrease in the sample temperature in the region of T < T-c approximate to 15 K is accompanied by a transition to a coherent regime of the spin density fluctuations. As a result, the ferromagnetic character of the interaction leads to the formation of magnetic microdomains with a characteristic size similar to 10 Angstrom. The exchange-induced magnetization enhancement in the vicinity of charge carriers in these microdomains probably accounts for the anomalous components in the Hall coefficient and the magnetization hysteresis observed in FeSi at LHe temperatures. The nature of the low-temperature transition at T-m approximate to 7 K in the system of interacting magnetic microparticles in iron monosilicide is discussed. (C) 2001 MAIK Nauka/Interperiodica.