Ferroelectricity out of magnetic frustration

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Responding electrically to magnetic stimuli and vise versa, multiferroics offer exciting possibilities for applications and challenge our understanding of coupled lattice and spin degrees of freedom in solids. I discuss how multiferroic properties can develop in frustrated magnets where competing interactions produce non-collinear spin order and symmetry breaking lattice distortions. Our experiments in TbMnO3, Ni3V2O8, and RbFe(MoO4)2 show that when the low temperature magnetic order breaks spatial inversion symmetry it is accompanied by ferroelectricity [1-3]. Conversely, the application of an electric field favors one of the two inversion symmetry related antiferromagnetic domains. We infer that inversion symmetry breaking magnetic order acts as an effective electric field through magneto-elastic distortions that relieve frustration. We also present evidence for microscopic correspondence between the ferroelectric and the antiferromagnetic domain structure. The results presented are based on magnetic neutron diffraction, pyrocurrent measurements, and theoretical work by A. B. Harris [4]. [1] M. Kenzelmann, A. B. Harris, S. Jonas, C. Broholm, J. Schefer, S. B. Kim, C. L. Zhang, S.-W. Cheong, O. P. Vajk, and J. W. Lynn, Phys. Rev. Lett. 95, 087206 (2005). [2] G. Lawes, A. B. Harris, T. Kimura, N. Rogado, R. J. Cava, A. Aharony, O. Entin-Wohlman, T. Yildirim, M. Kenzelmann, C. Broholm, and A. P. Ramirez, Phys. Rev. Lett. 95, 087205 (2005). [3] M. Kenzelmann, G. Lawes, A.B. Harris, G. Gasparovic, C. Broholm, A.P. Ramirez, G.A. Jorge, M. Jaime, S. Park, Q. Huang, A.Ya. Shapiro, and L.A. Demianets, Phys. Rev. Lett. 98, 267205 (2007). [4] A. B. Harris, Phys. Rev. B 76 , 054447 (2007).