SPIN DYNAMICS OF THE ITINERANT HELIMAGNET MNSI STUDIED BY POSITIVE MUON SPIN RELAXATION

The local magnetic fields and spin dynamics of the itinerant helimagnet MnSi (Tc 29.5 K) have been studied experimentally using positive muon spin rotation and relaxation (+SR) methods. In the ordered phase (T<Tc), zero-field SR was used to measure the hyperfine fields at the muon sites as well as the muon spin-lattice relaxation time T1. Two magnetically inequivalent interstitial + sites were found with hyperfine coupling constants Ahf(1)=-3.94 kOe/B and Ahf(2)=-6.94 kOe/B, respectively. In the paramagnetic phase (T>Tc), the muon nuclear-spin double-relaxation technique was used to simultaneously but independently determine the spin-lattice relaxation time T1Mn of Mn55 spins and that of positive muons (T1) over a wide temperature range (Tc<T 150 K). The temperature dependence of T1Mn and T1 in both phases shows systematic deviations from the predictions of self-consistent renormalization theory. © 1990 The American Physical Society.