The stability of magnetostrophic waves is considered in a horizontal thin plane layer of a perfectly conducting fluid, which is stratified according to gravitation and permeated by a variable toroidal magnetic field. The layer rotates rigidly around an axis inclined to the horizontal plane. It is shown that unstable magnetostrophic waves, driven by magnetic buoyancy, are capable of inducing an electromotive force parallel to the toroidal magnetic field. This dynamic effect is an alternative to the kinematic α-effect and of importance for the dynamo theory of strong magnetic fields. For parameters of the lower convection zone of the sun the process leads to an effective α of a few cm/s. The dynamo action for various angles of inclination is discussed.