  Coulomb interaction between two closely spaced parallel layers of electron
system can generate the frictional drag effect by interlayer Coulomb
scattering. Employing graphene double layers separated by few layer hexagonal
boron nitride (hBN), we investigate density tunable magneto- and Hall-drag
under strong magnetic fields. The observed large magneto-drag and Hall-drag
signals can be related with Laudau level (LL) filling status of the drive and
drag layers. We find that the sign and magnitude of the magneto- and Hall-drag
resistivity tensor can be quantitatively correlated to the variation of
magneto-resistivity tensors in the drive and drag layers, confirming a
theoretical formula for magneto-drag in the quantum Hall regime. The observed
weak temperature dependence and $\sim B^2$ dependence of the magneto-drag are
qualitatively explained by Coulomb scattering phase-space argument.
