  Criticality with strong coupling is described by a theory in the vicinity of
a non-Gaussian fixed point. The holographic duality conjectures that a theory
at a non-Gaussian fixed point with strong coupling is dual to a gravitational
theory. In this paper, we present a holographic theory in treating the strongly
coupled critical spin fluctuations in quasi-2-dimension. We show that a
universal frequency over temperature scaling law is a rather general property
of the critical ac spin susceptibility at strongly coupled limit. Explicit
results for the dynamic scaling of spin susceptibility are obtained in large-N
and large 't Hooft limit. We argue that such critical scaling are in good
agreement with a number of experiments, some of which can not be explained by
any perturbative spin-density-wave theory. Our results strongly suggest that
the anomalous behavior of non-Fermi liquids in materials is closely related to
the spin fluctuations described through the non-Gaussian fixed point. The
exotic properties of non-Fermi liquids can be viewed as the Fermi liquids
coupling to strongly coupled critical spin fluctuations.
