On adding ammonia in aqueous solution of $\mathrm{N}{\mathrm{i}}^{2+}$ containing $\left[\mathrm{N}\mathrm{i}\right({\mathrm{H}}_2\mathrm{O}{)}_6{]}^{2+}$ a new complex is formed as follows
$\underset{\underset{{\mathrm{\mu }}_{\mathrm{e}\mathrm{f}\mathrm{f}}=2.8\mathrm{B}\mathrm{M}}{\mathrm{s}{\mathrm{p}}^3{\mathrm{d}}^2\mathrm{H}\mathrm{y}\mathrm{b}.}}{\left[\mathrm{N}\mathrm{i}\right({\mathrm{H}}_2\mathrm{O}{)}_6{]}^{2+}}+6\mathrm{N}{\mathrm{H}}_3\rightleftharpoons \underset{\underset{{\mathrm{\mu }}_{\mathrm{e}\mathrm{f}\mathrm{f}}=2.8\mathrm{B}\mathrm{M}}{\mathrm{s}{\mathrm{p}}^3{\mathrm{d}}^2\mathrm{H}\mathrm{y}\mathrm{b}.}}{\left[\mathrm{N}\mathrm{i}\right(\mathrm{N}{\mathrm{H}}_3{)}_6{]}^{2+}}+6{\mathrm{H}}_2\mathrm{O}$
As there is no change in hybridisation and number of unpaired electrons so magnetic moment remains same.