Excitation of a large-scale magnetic field in a galactic disk surrounded by a gaseous corona

The evolution of the large-scale magnetic field in the disk of a spiral galaxy surrounded by a gaseous corona is considered. The diamagnetic effect can amplify the large-scale magnetic field in the galactic disk. During the amplification of the field via turbulent diamagnetism, both the ratio of the magnetic diffusion coefficients in the disk and corona and the thickness of the corona are important. In a disk embedded in a thick corona with parameters characteristic of spiral galaxies, a dipole magnetic-field configuration is generated, but is much weaker than the quadrupole field.