  Employing first principles density functional calculations, together with
solution of the low-energy, model Hamiltonian constructed in a first principles
manner, we explored the origin of magnetism and $T_c$ trend in Cr-based double
perovskite series, Sr$_2$CrB$'$O$_6$ (B$'$=W/Re/Os). Our study shows that the
apparently puzzling $T_c$ trend in Sr$_2$CrB$'$O$_6$ (B$'$=W/Re/Os) series can
be understood in terms of the interplay of the hybridization driven mechanism
and the super-exchange mechanism.
