Electron Spin Resonance in the Itinerant-Electron Helical Magnet MnSi

Electron spin resonance in MnSi single crystals was observed both above and below the transition temperature T N . The experimental results below T N were explained by applying the helical spin resonance theory developed by Copper and Elliott and the effective exchange fields { J ( q 0 )- J (0)} S / g µ B and { J (0)- J (2 q 0 )} S / g µ B were obtained as 3.0 kOe and 1.0 kOe, respectively, where q 0 is the screw vector. A dynamical anisotropy field should be taken into account to explain the experimental results. The paramagnetic resonance intensity above T N decreases strongly as temperature increases.