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Séminaire Magnétisme frustré

Jeudi 27 Février à 14h00,
Salle Remy Lemaire, K223

Orateur : Mathieu Pasturel (Institut des Sciences Chimiques de Rennes)
"The Kagomé antiferromagnet U3Ru4Al12 (and related compounds)"


The Kagomé antiferromagnet U3Ru4Al12 (and related compounds) The investigation and comprehension of magnetic frustrations is quite a hot topic for solid state physicists today [1]. Triangular, tetrahedral or Kagomé lattices, where magnetic moments cannot order in a perfect antiferromagnetic structure, are favorable for the occurrence of such geometrical frustrations.

The hexagonal Gd3Ru4Al12 structure-type [2] can be a good candidate for frustrated systems, as long as the magnetic atoms (rare earth, RE) are forming triangles with short interatomic distances (order of magnitude of the sum of metallic radii) connected the one to each other via much larger triangles, forming a distorted planar Kagomé network. In accordance with this geometry the uranium aluminides U3T4+xAl12-x (T = Fe, Co) present a spin glass behavior [3,4].

In this context, more surprising is the antiferromagnetic (AF) ordering of U3Ru4Al12 evidenced at TN = 8.4 K on a polycristalline sample [5]. The investigation of a single crystal of this phase [6] reveals a strong anisotropy of the physical properties. The AF peak is observed on the temperature dependence of the susceptibility curve measured along the a-axis while only a broad hump is observed at lower temperature along the c-axis. Neutron diffraction experiments revealed an original spin ice arrangement in the magnetically ordered state, with magnetic moments lying inside the (a,b) plane. Further characterizations including specific heat under magnetic field (up to 14 T) and magnetization under pulsed high magnetic field (up to 60 T) were undertaken to describe the magnetic phase diagram of this compound, raising quite some questions still unsolved.

In order to better understand the frustration mechanism in this structure type, other isostructural aluminides RE3T4Al12 (T = Co, Ru) [7,8] have been synthesized and magnetically characterized.

This presentation will thus focus on the cristallochemistry of these aluminides and on the description of their physical properties, mainly dealing with the advanced characterization of the antiferromagnet U3Ru4Al12.

References :
[1] L. Balents, Nature, 464 (2010) 199.
[2] R. E. Gladyshevskii et al., Acta Cryst. B, 49 (1993) 474.
[3] O. Tougait et al., Phil. Mag., 87 (2007) 1085.
[4] A. P. Gonçalves et al., Intermetallics, 17 (2009) 25.
[5] M. Pasturel et al., J. Phys. : Cond. Matter, 21 (2009) 125401.
[6] R. Troć et al., Phys. Rev. B, 85 (2012) 064412.
[7] W. Ge et al., J. Phys. : Conf. Ser., 344 (2012) 012023

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