Zero-field muon spin relaxation

Fig. 51. Zero-field muon-spin-relaxation function, Gj(t), observed in the spin glass CuMn5atom% (T, = 27.4 K) at various temperatures. The solid lines represent the best-fit curves for eq. 76 with the values of fl, and Aj given in fig. 52 (from Uemura et al. 1984).

Zero-field and longitudinal-field muon spin relaxation (ZF-/[Pg.281]

Muon Spin Relaxation refers to the observation of incoherent motions of the muon spins which result in a loss of polarization with time. This will occur if the magnetic field sensed by the ensemble of implanted muons is broadly distributed. If the local field each muon sees in addition fluctuates randomly during a muon s life we observe what is called dynamic depolarization , but also a stationary distributed field causes depolarization by phase incoherence ( static depolarization ). These two cases must be clearly distinguished. The situation corresponds to the two relaxation times Ty (spin-lattice) and Ti (spin-spin) in NMR. Muon Spin Relaxation measurements can be carried out without observing spin rotation and thus are possible in zero applied field or with a longitudinally applied field (i.e., a field applied parallel to the muon spin direction at the moment of implantation). Longitudinal field measurements are the most appropriate way to obtain a clear distinction between static and dynamic muon spin depolarization. Muon Spin Relaxation hence mostly refers to zero or longitudinal field (iSR. 

The dilute spin glasses are a special topic within p,SR because they generate distinctive muon spin relaxation via the Lorentzian field distribution. This was discussed as a possible field distribution (eq. 33) for p,SR in sect. 3.2.2 (the static ZF relaxation fimction, eq. (34), is shown in fig. 20). Whereas the Gaussian field distribution is expected (and often observed) in dense-moment systems, Walstedt and Walker (1974) predicted that the Lorentzian distribution applies in the dilute-moment limit (magnetic concentration goes to zero) of spin glasses, and Uemura and collaborators (Uemura et al. 1985, and references cited therein) observed it with xSR in the frozen state of dilute Cu(Mn) and Au(Fe). 

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