  We report a metal-insulator transition (MIT) in the half-filled multiorbital
antiferromagnet (AF) BaMn$_2$Bi$_2$ that is tunable by a magnetic field
perpendicular to the AF sublattices. Instead of an Anderson-Mott mechanism
usually expected in strongly correlated systems, we find by scaling analyses
that the MIT is driven by an Anderson localization. Electrical and
thermoelectrical transport measurements in combination with electronic band
calculations reveal a strong orbital-dependent correlation effect, where both
weakly and strongly correlated $3d$-derived bands coexist with decoupled charge
excitations. Weakly correlated holelike carriers in the $d_{xy}$-derived band
dominate the transport properties and exhibit the Anderson localization,
whereas other $3d$ bands show clear Mott-like behaviors with their spins
ordered into AF sublattices. The tuning role played by the perpendicular
magnetic field supports a strong spin-spin coupling between itinerant holelike
carriers and the AF fluctuations, which is in sharp contrast to their weak
charge coupling.
