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 gal axy surrounded by a gaseous corona is considered. The diamagnetic effect ca n amplify the large-scale magnetic field in the galactic disk. During the a mplification of the field via turbulent diamagnetism, both the ratio of the magnetic diffusion coefficients in the disk and corona and the thickness o f the corona are important. In a disk embedded in a thick corona with param eters characteristic of spiral galaxies, a dipole magnetic-field configurat ion is generated, but is much weaker than the quadrupole field.