. . . . . . . . . T/T$_{c}$ − 1 T ( K ) Lovesey and Engdahl Mode coupling 4 FIG. 4: (Color online.) Relaxation rate as a function of tem- perature in the paramagnetic regime for pure EuO (solid cir- cles) and (b) Eu 0 . 994 Gd 0 . 006 O (dots). The predicted relax- ation rates for T > T C according to Ref. 15 (numerical cal- culation: thick solid line  purple; critical regime using experi- mental values of correlation length: thick dashed line  purple) and Ref. 16 (dotted line  blue) are also shown. 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. [3] P. Sinjukow and W. Nolting  Phys. Rev. B 68   125107 (2003). [2] Y. Shapira  S. Foner and T. B. Reed  Phys. Rev. B 8   2299 (1973). [1] B. T. Matthias  R. M. Bozorth and J. H. van Vleck  Phys. Rev. Lett. 7   160 (1961). ∗ Electronic address: s.blundell@physics.ox.ac.uk [29] M. L. Brooks  T. Lancaster  S. J. Blundell  W. Hayes  F. L. Pratt and Z. Fisk  Phys. Rev. B 70   020401(R) (2004). [28] C. S. Snow  S. L. Cooper  D. P. Young  Z. Fisk  A. Comment and J.-P. Ansermet  Phys. Rev. B 64   174412 (2001). [27] A. D. Bruce and A. Aharony  Phys. Rev. B 10   2078 (1974). [26] J. Als-Nielsen  O. W. Dietrich  W. Kunnmann and L. Passell  Phys. Rev. Lett. 27   741 (1971). [25] V.G. Storchak  O.E. Parfenov  J.H. Brewer  P.L. Russo  S.L. Stubbs  R.L. Lichti  D.G. Eshchenko  E. Morenzoni  V.P. Zlomanov  A.A. Vinokurov and V.G. Bamburov  Physica B 404   899 (2009). [24] V.G. Storchak  O.E. Parfenov  J.H. Brewer  P.L. Russo  S.L. Stubbs  R.L. Lichti  D.G. Eshchenko  E. Morenzoni  T.G. Aminov  V.P. Zlomanov  A.A. Vinokurov  R.L. Kallaher and S. von Moln´ ar  Phys. Rev. B 80   235203 (2009). [23] V. G. Storchak  J. H. Brewer  D. J. Arseneau  S. L. Stubbs  O. E. Parfenov  D. G. Eshchenko  E. Morenzoni and T. G. Aminov  Phys. Rev. B 79   193205 (2009). [22] D.G. Eshchenko  V.G. Storchak  E. Morenzoni and D. Andreica  Physica B 404   903 (2009). [21] A. Kasuya and M. Tachiki  Phys. Rev. B 8   5298 (1973). [20] S. J. Blundell  Physica B 404   581  (2009). [19] A. Comment  J.-P. Ansermet  C. P. Slichter  H. Rho  C. S. Snow and S. L. Cooper  Phys. Rev. B 72   014428 (2005). [18] P. Dalmas de R´eotier and A. Yaouanc  J. Phys. C 9   9113  (1997). [17] S. F. J. Cox  J. Phys. C 20   3187  (1987); S. J. Blundell  Contemp. Phys. 40   175  (1999). [16] A. Yaouanc  P. Dalmas de R´eotier and E. Frey  Phys. Rev. B 47   796 (1993). [15] S. W. Lovesey and E. Engdahl  J. Phys.: Condens. Mat- ter 7   769 (1995). [14] S. W. Lovesey and E. B. Karlsson and K. N. Trohidou  J. Phys.: Condens. Matter 4   2043 (1992); S. W. Lovesey  K. N. Trohidou and E. B. Karlsson J. Phys.: Condens. Matter 4   2061 (1992). [13] H. G. Bohn  W. Zinn  B. Dorner and A. Kollmar  Phys. Rev. B 22   5447 (1980). [12] A. Mauger and C. Godart  Phys. Rep. 141   51 (1986). [11] Ven-Chung Lee and L. Liu  Phys. Rev. B 30   2026 (1984). [10] H. Miyazaki  T. Ito  H. J. Im  S. Yagi  M. Kato  K. Soda and S. Kimura  Phys. Rev. Lett. 102   227203 (2009). [9] O. W. Dietrich  J. Als-Nielsen and L. Passell  Phys. Rev. B 14   4923 (1976); J. Als-Nielsen  O. W. Dietrich and L. Passell  Phys. Rev. B 14   4908 (1976); L. Passell  O. W. Dietrich and J. Als-Nielsen  Phys. Rev. B 14   4897 (1976). [8] A. Schmehl et al. Nat. Mat. 6   882 (2007). [7] P. G. Steeneken  L. H. Tjeng  I. Elfimov  G. A. Sawatzky  G. Ghiringhelli  N. B. Brookes and D.-J. Huang  Phys. Rev. Lett. 88   047201 (2002). [6] K. Sattler and H. C. Siegmann  Phys. Rev. Lett. 29   1565 (1972). [5] K. J. Hubbard and D. G. Schlom  J. Mater. Res. 11   2757 (1996). [4] J. B. Torrance  M. W. Shafer and T. R. McGuire  Phys. Rev. Lett. 29   1168 (1972).