Influence of the diamagnetic effect on the magnetorotational instability in accretion discs

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We show that in protostellar discs the diamagnetic effect modifies the magnetorotational instability (MRI) that exists in the presence of the Hall electromotive force. We also make clear that the inclusion of magnetization into the governing magnetohydrodynamics equations does not weaken the unstable character of the disc. The maximum growth rate of the unstable mode exceeds the local Oort A-value. Another novel result is that the magnetic field gradient produced by the magnetization current in active zones produces an unstable mode, which drives the MRI when the magnetic moment and rotation axes are perpendicular.