  This paper demonstrates the anisotropic response of quantum critical
fluctuations with respect to the direction of the magnetic field $B$ in
Ni-doped CeCoIn$_5$ by measuring the magnetization $M$ and specific heat $C$.
The results show that $M/B$ at $B=0.1\ {\rm T}$ for both the tetragonal $c$ and
$a$ directions exhibits $T^{-\eta}$ dependencies, and that $C/T$ at $B=0$
follows a $-\ln T$ function, which are the characteristics of non-Fermi-liquid
(NFL) behaviors. For $B\,||\,c$, both the $M/B\propto T^{-\eta}$ and $C/T
\propto -\ln T$ dependencies change into nearly temperature-constant behaviors
by increasing $B$, indicating a crossover from the NFL state to the
Fermi-liquid state. For $B\,||\,a$, however, the NFL behavior in $C/T$ persists
up to $B=7\ {\rm T}$, whereas $M/B$ exhibits temperature-independent behavior
for $B\ge 1\ {\rm T}$. These contrasting characteristics in $M/B$ and $C/T$
reflect the anisotropic nature of quantum critical fluctuations; the $c$-axis
spin component significantly contributes to the quantum critical fluctuations.
We compare this anisotropic behavior of the spin fluctuations to
superconducting properties in pure CeCoIn$_5$, especially to the anisotropy in
the upper critical field and the Ising-like characteristics in the spin
resonance excitation, and suggest a close relationship between them.
