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Coupling of frustrated ising spins to the magnetic cycloid in multiferroic TbMnO3Prokhnenko, O.; Feyerherm, R.; Mostovoy, Maxim; Aliouane, N.; Dudzik, E.; Maljuk, A.; Argyriou, D. N. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.

X-ray resonant magnetic scattering studies of rare-earth magnetic ordering were performed on perovskite manganites RMnO 3 ͑R =Dy,Gd͒ in an applied magnetic field. The data reveal that the field-induced threefold polarization enhancement for H ʈ a͑H Ϸ 20 kOe͒ observed in DyMnO 3 below 6.5 K is due to a re-emergence of the Mn-induced Dy spin order with propagation vector Dy = Mn = 0.385b ‫ء‬ , which accompanies the suppression of the independent Dy magnetic ordering, Dy =1/ 2b ‫ء‬ . For GdMnO 3 , the Mn-induced ordering of Gd spins is used to track the Mn-ordering propagation vector. The data confirm the incommensurate ordering reported previously, with Mn varying from 0.245b ‫ء‬ to 0.16b ‫ء‬ on cooling from T N Mn down to a transition temperature TЈ.New superstructure reflections which appear below TЈ suggest a propagation vector Mn =1/ 4b ‫ء‬ in zero magnetic field, which may coexist with the previously reported A-type ordering of Mn. The Gd spins order with the same propagation vector below 7 K. Within the ordered state of Gd at T = 1.8 K we find a phase boundary for an applied magnetic field H ʈ b, H = 10 kOe, which coincides with the previously reported transition between the ground-state paraelectric and the ferroelectric phases of GdMnO 3 . Our results suggest that the magnetic ordering of Gd in magnetic field may stabilize a cycloidal ordering of Mn that, in turn, produces ferroelectricity.