  We theoretically investigate zero-temperature magnetic ordering of mixtures
of spin-1 (alkali atoms) and spin-0 (alkaline-earth atoms) bosons in a
three-dimensional optical lattice. With the single-mode approximation for the
spin-1 bosons, we obtain an effective Bose-Hubbard model for describing the
heteronuclear mixtures in optical lattices. By controlling the interspecies
interactions between alkali and alkaline-earth atoms, we map out complete phase
diagrams of the system with both positive and negative spin-dependent
interactions for spin-1 atoms, based on bosonic dynamical mean-field theory. We
find that the spin-1 components feature ferromagnetic and nematic insulating
phases, in addition to the superfluid, depending on spin-dependent
interactions. Take the spin-1 alkali bosons as spin $\uparrow$, and spin-0
alkaline-earth bosons as spin $\downarrow$, we observe that the system favors
ferromagnetic insulator at filling $n=1$, and unorder insulator at $n=2$.
Interestingly, we observe a two-step Mott-insulating-superfluid phase
transition, as a result of mass imbalance between alkali and alkaline-earth
atoms.
