  We investigate the three-dimensional Anderson model of localization via a
modified transfer-matrix method in the presence of scale-free diagonal disorder
characterized by a disorder correlation function $g(r)$ decaying asymptotically
as $r^{-\alpha}$. We study the dependence of the localization-length exponent
$\nu$ on the correlation-strength exponent $\alpha$. % For fixed disorder $W$,
there is a critical $\alpha_{\rm c}$, such that for $\alpha < \alpha_{\rm c}$,
$\nu=2/\alpha$ and for $\alpha > \alpha_{\rm c}$, $\nu$ remains that of the
uncorrelated system in accordance with the extended Harris criterion. At the
band center, $\nu$ is independent of $\alpha$ but equal to that of the
uncorrelated system. The physical mechanisms leading to this different behavior
are discussed.
