Spin Fluctuations of Itinerant Electrons in MnSi Studied by Muon Spin Rotation and Relaxation

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Abstract
The static and the dynamic character of the hyperfine field in weak itinerant helimagnet MnSi has been probed by using positive muon spins. The Knight shift has been measured by the transverse-field muon spin rotation method, which revealed a large negative hyperfine field at interstitial sites, even larger compared with other ferromagnetic metals. The hyperfine coupling constant A hf has been determined to be -4.8 kOe/µ B . The divergence of the muon spin-lattice relaxation rate near magnetic ordering has been observed for the first time by using the longitudinal-field muon spin relaxation method. The observed temperature dependence was found to be in agreement with the prediction of the self-consistent renormalization theory of itinerant electron spin fluctuations developed by Moriya and his collaborators.