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cooling to T$_{C}$ from about 0.3 K above it; this is also not observed in our data. Magnetic polaron formation has been detected using Raman scattering [28] in a narrow range ( ≈ 20 K) above T$_{C}$ . It may be that the forma- tion of magnetic polarons modifies the relaxation in this regime from that which would be expected from theory, perhaps by providing an additional relaxation channel for the muon which masks the critical slowing down pre- dicted by the theory and hence the absence of the diver- gence in λ . We note that a similar absence of a divergence in λ is observed in EuB$_{6}$ [29] in which magnetic polarons have been found [28]. 

In conclusion, we have identified the muon site in EuO and estimated the hyperfine field. Our results confirm long-range order which is relatively insensitive to low doping of Gd. The measured λ in the paramagnetic state agrees quite well with the theory of Lovesey and Engdahl, but the available theories fail in the critical regime, pos- sibly due to magnetic polaron formation. 

We thank EPSRC (UK) for financial support and Alex Amato for experimental assistance. Part of this work was performed at the Swiss Muon Source, Paul Scherrer Institute, Villigen, Switzerland. 

∗ Electronic address: s.blundell@physics.ox.ac.uk 

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