  We present a numerical study of quasistatic magnetoconvection in a cubic
Rayleigh-B\'enard (RB) convection cell subjected to a vertical external
magnetic field. For moderate values of the Hartmann number Ha, we find an
enhancement of heat transport. Furthermore, a maximum heat transport
enhancement is observed at certain optimal $Ha_{opt}$. The enhanced heat
transport may be understood as a result of the increased coherency of the
thermal plumes, which are elementary heat carriers of the system. To our
knowledge this is the first time that a heat transfer enhancement by the
stabilising Lorentz force in quasistatic magnetoconvection has been observed.
We further found that the optimal enhancement may be understood in terms of the
crossing between the thermal and the momentum boundary layers (BL) and the fact
that temperature fluctuations are maximum near the position where the BLs
cross. These findings demonstrate that the heat transport enhancement
phenomenon in the quasistatic magnetoconvection system belongs to the same
universality class of stabilising$-$destabilising ($S$-$D$) turbulent flows as
the systems of confined Rayleigh-B\'enard (CRB), rotating Rayleigh-B\'enard
(RRB) and double-diffusive convection (DDC). This is further supported by the
findings that the heat transport, boundary layer ratio and the temperature
fluctuations in magnetoconvection at the boundary layer crossing point are
similar to the other three cases.
