  We present long-term (~10^4 M) axisymmetric simulations of differentially
rotating, magnetized neutron stars in the slow-rotation, weak magnetic field
limit using a perturbative metric evolution technique. Although this approach
yields results comparable to those obtained via nonperturbative (BSSN)
evolution techniques, simulations performed with the perturbative metric solver
require about 1/4 the computational resources at a given resolution. This
computational efficiency enables us to observe and analyze the effects of
magnetic braking and the magnetorotational instability (MRI) at very high
resolution. Our simulations demonstrate that (1) MRI is not observed unless the
fastest-growing mode wavelength is resolved by more than about 10 gridpoints;
(2) as resolution is improved, the MRI growth rate converges, but due to the
small-scale turbulent nature of MRI, the maximum growth amplitude increases,
but does not exhibit convergence, even at the highest resolution; and (3)
independent of resolution, magnetic braking drives the star toward uniform
rotation as energy is sapped from differential rotation by winding magnetic
fields.
