The Ag metallic host doped with Gd and Sb is an excellent model system to study the bottleneck effect associated to the conduction-electron (c-e) spin-flip scattering mechanism. Electron spin resonance of Gd3 + in both, Ag-(Gd doped)- and Ag-(Gd and Sb doped)-systems, reveal the presence of bottleneck which can be tuned by the amount of Gd and Sb impurities. The increase of the Gd concentration leads to a c-e spin-flip relaxation rate to the magnetic Gd3 + ions larger than that to the lattice, favoring the bottleneck regime. Whereas the effect of the non-magnetic impurities (Sb ions) is to increase, via spin-orbit scattering, the spin-flip relaxation rate of the c-e to the lattice, weakening the bottleneck regime. © 2009 Elsevier B.V. All rights reserved.4041827232725Zvyagin, A.A., Makarova, A.V., (2005) J. Phys. Condens. Matter, 17, p. 1251Barnes, S.E., (1981) Adv. Phys., 30, p. 801Taylor, R.H., (1975) Adv. Phys., 24, p. 681Overhauser, A.W., (1953) Phys. Rev., 89, p. 689Oseroff, S., Gehman, B., Schultz, S., Rettori, C., (1975) Phys. Rev. Lett., 35, p. 679Davidov, D., Rettori, C., Dixon, A., Baberschke, K., Chock, E.P., Orbach, R., (1973) Phys. Rev. B, 8, p. 3563Feher, G., Kip, A.F., (1955) Phys. Rev., 98, p. 337Dyson, F.J., (1955) Phys. Rev., 98, p. 349Pake, G.E., Purcell, E.M., (1948) Phys. Rev., 74, p. 1184Davidov, D., Maki, K., Orbach, R., Rettori, C., Chock, E.P., (1973) Solid State Commun., 12, p. 621Rettori, C., Kim, H.M., Chock, E.P., Davidov, D., (1974) Phys. Rev. B, 10, p. 1826Rettori, C., Oseroff, S.B., Rao, D., Pagliuso, P.G., Barberis, G.E., Sarrao, J., Fisk, Z., Hundley, M., (1997) Phys. Rev. B, 55, p. 1016Narath, A., (1967) Phys. Rev., 163, p. 232Shaw, R.W., Warren, W.W., (1971) Phys. Rev. B, 3, p. 1562Davidov, D., Rettori, C., Orbach, R., Dixon, A., Chock, E.P., (1975) Phys. Rev. B, 11, p. 3546