It is considered a model of the tangential breakup, formed by the two elastic half-spaces separated by a vacuum diamagnetic gap. One of the half-spaces moves with given velocity. The stability of this gap in relation to small perturbations in the form of surface waves is studied. The existence of diamagnetic gap in this case leads to the generating two types of surface waves with different phase velocities. It has been shown that perturbations will be unstable in the case when the value of the speed of the half-space is found in the interval between double phase velocities.