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Antiferroelectric resonance in noncentrosymmetric multi-sublattice magnets

We predict the phenomenon of antiferroelectric resonance (AFER), in which an ac electric field causes magnetic ions located at noncentrosymmetric positions in a multi-sublattice magnet to undergo magnetic transitions corresponding to exchange collective excitations of the system. We construct a theory of such resonances, and show that in magnets with collinear magnetic structures AFER is caused by relativistic and exchange-relativistic magnetoelectric interactions, while in the noncollinear magnets a significant contribution can also come from the exchange magnetoelectric interaction. We predict an exchange enhancement of the resonance by exchange modes, and discuss the role of AFER in causing resonant enhancement of magnetooptical phenomena. The main results of our theory are illustrated with the four-sublattice rhombohedral antiferromagnets α-Fe_2O_3 and Cr_2O_3, as examples.