  The temperature (T) dependence of the muon and $^{63}$Cu nuclear spin-lattice
relaxation rates $1/T_1$ in YbCu4.4Au0.6 is reported over nearly four decades.
It is shown that for $T\to 0$ $1/T_1$ diverges following the behaviour
predicted by the self-consistent renormalization (SCR) theory developed by
Moriya for a ferromagnetic quantum critical point. On the other hand, the
static uniform susceptibility $\chi_s$ is observed to diverge as $T^{-2/3}$ and
$1/T_1T\propto \chi_s^2$, a behaviour which is not accounted for by SCR theory.
The application of a magnetic field $H$ is observed to induce a crossover to a
Fermi liquid behaviour and for $T\to 0$ $1/T_1$ is found to obey the scaling
law $1/T_1(H)= 1/T_1(0)[1+(\mu_BH/k_BT)^2]^{-1}$.
