  We solve for the local vertical structure of a thin accretion disk threaded
by a poloidal magnetic field. The angular velocity deviates from the Keplerian
value as a result of the radial Lorentz force, but is constant on magnetic
surfaces. Angular momentum transport and energy dissipation in the disk are
parametrized by an alpha-prescription, and a Kramers opacity law is assumed to
hold. We also determine the stability of the equilibria with respect to the
magnetorotational (or Balbus-Hawley) instability. If the magnetic field is
sufficiently strong, stable equilibria can be found in which the angle of
inclination, i, of the magnetic field to the vertical at the surface of the
disk has any value in the range [0,90 degrees). By analyzing the dynamics of a
transonic outflow in the corona of the disk, we show that a certain potential
difference must be overcome even when i > 30 degrees. We determine this
potential difference as a function of i for increasing values of the vertical
magnetic field strength. For magnetorotationally stable equilibria, the
potential difference increases faster than the fourth power of the magnetic
field strength, quickly exceeding a value corresponding to the central
temperature of the disk, and is minimized with respect to i at i approximately
equal to 38 degrees. We show that this property is relatively insensitive to
the form of the opacity law. Our results suggest that an additional source of
energy, such as coronal heating, may be required for the launching of an
outflow from a magnetized disk.
