Critical slowing down in Zn-Mg-Ho quasicrystal

By means of longitudinal field muon-spin spectroscopy, we have found a clear critical slowing down caused by spin fluctuation of Ho moments in the icosahedral quasicrystal (QC), i-ZnMgHo, with freezing temperature (T-f=1.95 K), for which the susceptibility showed an anomaly at 5 K. The difference is attributed to crystalline electric field (CEF) effects. The muons experience a broad, fluctuating, field distribution, of width Delta similar to 6.3 T around T-f. The effect of the CEF is also apparent in zero field and weak applied transverse field measurements, with an onset around 60 K. For the Cd-based QCs (CdMgHo and CdMgGd), which exhibited two freezing temperatures in the susceptibility, the change in fluctuation rate, i.e. freezing, occurs at the lower T-f.