Magnetoelastic effects and magnetization plateaus in two-dimensional systems

We show the importance of both strong frustration and spin-lattice coupling for the stabilization of magnetization plateaus in translationally invariant two-dimensional systems. We consider a frustrated spin-1/2 Heisenberg model coupled to adiabatic phonons under an external magnetic field. At zero magnetization, simple structures with two or at most four spins per unit cell are stabilized, forming dimers or 2x2 plaquettes, respectively. A much richer scenario is found in the case of magnetization m=1/2, where larger unit cells are formed with nontrivial spin textures and an analogy with the corresponding classical Ising model is detectable. Specific predictions on lattice distortions and local spin values can be directly measured by x rays and nuclear magnetic resonance experiments.