  The multifunctional materials with prominent properties such as electrical,
ferroelectric, magnetic, optical and magneto-optical are of keen interest to
several practical implications. In the roadmap of designing such materials, in
the present work, using density functional theory based first-principles
calculations, we have investigated the functional properties of transition
metal substituted-NBT. Our calculations predict the emergence of half-metallic
ferromagnetism in the system. A nonzero magnetic moment of 1.49 $\mu_{\rm
B}/{\rm f.u.}$ is obtained for 25\% concentration of Ni. Our data on optical
properties for pure NBT is in excellent agreement with available theory and
experiments. For Ni-NBT, we observed a diverging nature of static dielectric
constant, which could be attributed to the induced metallic character in the
material. Our simulations on MOKE predict a significant Kerr signal of
0.7$^\circ$ for 6.25\% Ni-concentration.
