Degenerate electronic Fermi system with intrinsic (spin) magnetic moment and Landau diamagnetic moment of the electrons in a neutron star interior is magnetized. Taking the magnetizing effect into consideration, the magnetic induced equation must be changed: the resulting equation has an additional magnetic induction term and a magnetic diffusion coefficient that is different from the original one for plasma. When effective magnetic diffusion coefficient equals critical value ( zero) the fully degenerate electronic system approaches a new phase. In this phase, the magnetic field of neutron star will become very large until other mechanisms suppress the increasing of the field in the neutron star lowered crust. For a stable or de Hass-Van Alphen oscillatory state, it is possible for the neutron star to become a magnetar .