We report on mu SR measurements probing the dynamic magnetic properties of
HoBa2Cu3O6+x and GdBa2Cu3O6+x powder samples with different oxygen content
x. While the longitudinal field relaxation rate in GdBa2Cu3O6+x does not in
dicate a change of the dynamics of the Gd magnetic moments as function of o
xygen content, there is a strong dependence of the dynamics of the Ho magne
tic moments in HoBa2Cu3O6+x. (C) 1999 Elsevier Science B.V. All rights rese
rved.