  We investigate the effect of Ni${\text -}$substitution on the crystalline
structure and the critical behavior of $Nd_{0.6}Sr_{0.4}Mn_{1-x}Ni_{x}O_{3}$
(0.00 $\leq$ x $\leq$ 0.20) perovskite. X${\text -}$ray diffraction patterns
revealed that the major phase in all samples is the orthorhombic structure with
space group $\textit{Pnma}$. Rietveld refinement revealed a linear reduction in
the lattice parameters along with monotonic reduction in the O2${\text
-}$Mn${\text -}$O2 angel with increasing Ni concentration. The modified Arrott
plots and the Kouvel${\text -}$Fisher method have been used to analyze the
magnetization isotherms near the paramagnetic to ferromagnetic (PM${\text
-}$FM) phase transition. The obtained critical exponents ($\beta$, $\gamma$ and
$\delta$) revealed that the Ni${\text -}$free sample is consistent with
3D${\text -}$Heisenberg like behavior. However, upon Ni${\text -}$substitution,
the critical exponents exhibit a mean field like behavior. The reliability of
the obtained critical exponent ($\beta$, $\gamma$ and $\delta$) values have
been confirmed by the universal scaling behavior of the isothermal
magnetization near the transition temperature.
