1. Spin glass behaviour in a new ternary intermetallic, U 3 Fe 4+x Al 12-x A.P. Gonçalves 1, O. Tougait 2, H. Noël 2 1 Departamento de Química, Instituto Tecnológico e Nuclear/CFMC-UL, Sacavém, Portugal 5 Sciences Chimiques de Rennes, Laboratoire de Chimie du Solide et Matériaux. UMR CNRS 6226, Université de Rennes 1, Avenue de Général Leclerc, 35042 Rennes, France

2. Outline Introduction Experimental Crystal structure Magnetic properties Conclusions

3. Phase equilibrium study of U-Fe-Al Introduction (1)UFe 2 Al 10 (2)U 2 Fe 4 Al 13 (3)UAl 2-x Fe x (4)U 3 Fe 4+x Al 12-x (5)UFe x Al 12-x (6)U 2 Fe 17­x Al x (7)UFe 1+x Al 1-x (8)U 2 Fe 12 Al 5 (9)UFe 2-x Al x R

4. U 3 Fe 4+x Al 12-x crystallizes in the Gd 3 Ru 4 Al 12 structure type

5. U atoms form a distorted Kagome net

6. Good candidate for spin glass due to geometrical frustration. ?

7. Samples prepared by arc-melting/annealing (850ºC, 2 weeks); Analyzed by powder XRD and Observed by SEM; Characterized by ac-susceptibility (30-10000 Hz, 1-500 Oe) and magnetization (ZFC/FC, 0-7 T) measurements between 2-300 K; Experimental

8. Crystal structure U 3 Fe 4 Al 12 P

9. AtomWyckoff positionxyzO.F.B iso, Å 2 U16h0.1972(2)0.3945(4)1/40.9(1.0)0.01* Al112k0.1589(8)0.318(2)0.9220(8)1.1(1.3)0.05* Al26h0.567(1)0.134(2)1/41.4(1.6)0.05* Al34f1/32/30.009(2)1.0(1.2)0.05* Al42b001/41.0(1.1)0.01* Fe16g1/5001.0(1.1)0.01* Fe22a0001.2(1.3)0.04* * - fixed parameter Cell parameters, Åa = 8.7516(3) c = 9.2653(4) RPRP 19.7 R WP 17.9 2 12.6 RBRB 7.86 RFRF 5.70 U 3 Co 4+x Al 12-x 8.7060(2) 9.2230(3) U 3 Co 4+x Al 12-x 8.7060(2) 9.2230(3) 0.1928(2)0.3857(3)1/4 0.1622(8)0.3244(2)0.9238(3) 0.5637(3)0.1274(3)1/4 1/32/30.0084(2) 001/4 1/500 000

10. -UFeAl 3

11. U-U = 3,553(2) Å U-Fe = 3,282(4) Å U-Al = 3,001(4) Å Fe-Al = 2,316(2) Å Fe-Fe = 4,358(1) Å

12. Magnetic properties μ

13. χ = C/(T- ) = -25.5(1) K, μ eff = 3.54(1) μ B (considered 1U:1Fe:3Al) μ eff (U 3+ ) = 3.62 μ B or μ eff (U 4+ ) = 3.58 μ B U intermetallics 2 – 3 μ B Fe contribution

16. R

18. T f / [T f log( )] Spin-glass: 0.004 - 0.03 (strong interactions between magnetic moments) Superparamagnets: 0.25 - 0.35 (weak interactions between clusters) U 3 Fe 4 Al 12 : 0.03 true spin-glass

19. Arrhenius law = 0 exp(-T A /T f ) Vogel-Fulcher law = 0 exp[-T A /(T f -T 0 )] 0 10 33 Hz and T A = E a /k B = 535 K Frequency dependence of the freezing temperature

20. 0 10 13 Hz

21. Conclusions U 3 Fe 4 Al 12 is a true spin glass; Fe magnetic contribution; Spin glass origin related to the topological frustration of the U moments and to the disorder at the Fe sites.

22. Acknowledgements GRICES/EGIDE 2007-2008;