Talk by Pascale Deen from ESS – Niels Bohr Institute - University of Copenhagen

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Talk by Pascale Deen from ESS

Spin dynamics in the hyperkagome compound Gd3Ga5O12

P. P. Deen1 . O. A. Petrenko2, G. Balakrishnan2, B. D. Rainford4 ,

C. Ritter3, L. Capogna3, H. Mutka3, T. Fennell3

1) European Spallation Source, Stora Algatan 4, SE-221 00 Lund, Sweden. 2) Department of Physics, University of Warwick, Coventry, CV4 7AL, U.K.. 3)Institut Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble, France. 4)Department of Physics and Astronomy, Southampton University, Southampton, SO17 0BJ, U.K.

Frustration is an unusual state of matter in which order cannot be achieved due to the presence of competing forces that cannot be simultaneously sat­isfied or geometric considerations [1]. Frustration is ubiquitous is nature and can be found in many types of materials ranging from liquid crystals, polymers to compounds with localised magnetic moments [2]. The study of magnetic frustration, in particular, is proving very fruitful in the development of a more general understanding.

The dynamic nature of magnetic frustration is governed by the connec­tivity of the many degenerate spin configurations and is thus one of the most interesting aspects of these systems. With this is mind we present the first neutron inelastic scattering results on the magnetic state of the frustrated hyperkagome Gd3Ga5O12 (GGG). GGG is unique since it offers the only opportunity to study frustration on a double hyperkagome structure. In ad­dition, although many frustrated compounds revert to an ordered state via an "order by disorder" transition [3] GGG shows no sign of long range order down to 25 mK despite a Curie-Weiss temperature of θCW ∼ -2 K [4 and references within].

Our neutron scattering studies suggest that the ground state of a three di­mensional hyperkagome compound differs distinctly from its frustrated coun­terparts on a pyrochlore lattice [4]. Indeed for a pyrochlore lattice a contin­uum of gapless excitations represents the manifold of degenerate states [5]. In contrast distinct gapped excitations are observed in GGG that can be assigned to zero energy modes thus endorsing a fundamental prediction for the kagome lattice [6,7 ].

[1] L. Balents. Nature 464, 08917, (2010), J. Gardner et al. Reviews of modern physics, 82, 53, (2010).[2] Jean-Franois Sadoc. Geometrical Frustration, Cambridge Books Online. [3] J. Villain et al. J. Physique 41, 1263-1272, (1980).

[4]P.P.Deen et al. Phys. Rev. B. 82, 174408 (2010). [5] R. Moessner et al. Phys. Rev. Lett. 80, 2929, (1998). [6] M.E.Zhitomirsky. Phys. Rev. B. 67, 104421 (2003). [7]J. Robert et al. Phys. Rev. Lett. 101, 117207 (2008)

Talk by Pascale Deen from ESS