Spin fluctuations in the temperature-induced paramagnet FeSi

Extensive polarized-neutron experiments have been performed on an FeSi single crystal in a temperature range between 150 and 600 K, and the first concrete evidence that FeSi exhibits temperature-induced magnetism is presented. The magnetic scattering depends strongly on q around ``ferromagnetic'' reciprocal-lattice points, but the integrated intensity over energy is independent of q. The magnetic moment M(q) deduced from the integrated intensity increases with increasing temperature and is in good agreement with the temperature variation of the magnetic moment calculated from the static susceptibility. The width of the energy spectrum depends strongly on both temperature and q. These results can be interpreted in terms of temperature-induced paramagnetism with a narrow-band-gap model.