  We discuss the problem of the formation of a large-scale magnetic field in
the accretion disks around black holes, taking into account the nonuniform
vertical structure of the disk. The high electrical conductivity of the outer
layers of the disk prevents the outward diffusion of the magnetic field.
  This implies a stationary state with a strong magnetic field in the inner
parts of the accretion disk close to the black hole, and zero radial velocity
at the surface of the disk. Magnetic jet collimation is considered, when the
jet radius is hold due to magneto-torsional oscillations. The range of
parameters is found where jet radius is oscillating, regularly or chaotically,
within restricted values.
