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, Rennes, France

Outline Introduction Experimental Crystal structure Magnetic properties Conclusions

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

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

U atoms form a distorted Kagome net

Good candidate for spin glass due to geometrical frustration. ?

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

Crystal structure U 3 Fe 4 Al 12 P

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 = (3) c = (4) RPRP 19.7 R WP RBRB 7.86 RFRF 5.70 U 3 Co 4+x Al 12-x (2) (3) U 3 Co 4+x Al 12-x (2) (3) (2)0.3857(3)1/ (8)0.3244(2)0.9238(3) (3)0.1274(3)1/4 1/32/ (2) 001/4 1/

-UFeAl 3

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

Magnetic properties μ

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

R

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

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

Hz

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.

Acknowledgements GRICES/EGIDE ;