  The intrinsic magnetic topological insulators, Mn(Bi1-xSbx)2Te4, in their
spin-aligned strong field configuration have been identified as a Weyl
semimetal with single pair of Weyl nodes1-4. A direct consequence of the Weyl
state is the layer-dependent Chern number (C) in thin film quantization.
Previous reports in MnBi2Te4 thin films revealed the higher C states in the
spin alignment by either increasing the film thickness5 or controlling chemical
potential into electron doping6-8. A clear picture of the higher Chern states
is still missing as the situation is complicated by the emerging of surface
band Landau levels (LLs) in magnetic field. Here, we report a tunable
layer-dependent of C= 1 state with the Sb substitutions by performing a
detailed analysis of the quantization states in Mn(Bi1-xSbx)2Te4 dualgated
devices, consistent with the calculations of the bulk Weyl point separations in
the compounds. The observed Hall quantization plateaus for our thicker
Mn(Bi1-xSbx)2Te4 films under strong magnetic fields can be interpreted from a
theory of surface and bulk spin-polarized Landau levels spectrum in thin film
magnetic topological insulators. Our results demonstrate that Mn(Bi1-xSbx)2Te4
thin films provide a highly tunable platform for probing the physics of the
anomalous Landau quantization that is strongly sensitive to magnetic order.
