Is MnSi an itinerant-electron magnet? Results of ESR experiments

High-frequency (60 GHz) electron spin resonance (ESR) has been studied in manganese monosilicide, MnSi, single crystals. The measurements performed within the $4.2{-}300$ K temperatures range at the applied magnetic field up to 70 kOe have demonstrated that the magnetic resonance in MnSi is due to localized magnetic moments of the Heisenberg type with the $g$–factor depending only slightly on temperature, $g\sim1.9{-}2$. At the same time, it has been found that the ESR linewidth is determined by spin fluctuations and can be quantitatively described in the wide temperature range ($4.2<T<60$ K) in the framework of the Moriya theory using the $S_L(T)$ function. The revealed deviations from the model of weak itinerant-electron magnetism commonly used for the description of the magnetic properties of MnSi indicate a possible spin-polaron nature of the unusual magnetic properties of this strongly correlated metal.