We consider a satellite in a Keplerian circular orbit in the Earth's gravitational and magnetic fields. The satellite's librational motion near gravitationally stable equilibrium position is investigated. With taking into account the non-linear terms up to the third order of smallness the spectral structure of the Lorentz torque is analyzed. Possible resonant combinations due to the disturbing torque in the attitude motion of gravity oriented satellite are revealed. Relevant curves are plotted on the plane of the dimensionless inertial parameters of the satellite.