Spin glass behaviour in a new ternary intermetallic, U3Fe4+xAl12-x

A.P. Gonçalves1, O. Tougait2, H. Noël2

1Departamento 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

Outline

•Introduction

•Experimental

•Crystal structure

•Magnetic properties

•Conclusions

•Phase equilibrium study of U-Fe-Al

Introduction

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

FeAl3Fe2Al5

FeAl2

UAl3

AlU

Fe

UFe

Al

L

L

UAl2

UFe2

FeAl

1

2

34

56

78

9

(1) UFe2Al10

(2) U2Fe4Al13

(3) UAl2-xFex

(4) U3Fe4+xAl12-x

(5) UFexAl12-x

(6) U2Fe17 xAlx

(7) UFe1+xAl1-x

(8) U2Fe12Al5

(9) UFe2-xAlx

R

•U3Fe4+xAl12-x crystallizes in the Gd3Ru4Al12 structure type

ab

cPowderCell 2.0

U atoms form a distorted Kagome net

a

b

cPowderCell 2.0

Good candidate for spin glass due to geometrical frustration.

a

b

cPowderCell 2.0

?

• 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

Crystal structure

20 40 60 80 100

0

10000

20000

30000

40000

* *

Yobs Ycal Yobs-Ycal

Inte

nsity

(au

)

2 teta (º)

U3Fe4Al12

P

Atom Wyckoff position x y z O.F. Biso, Å2

U1 6h 0.1972(2) 0.3945(4) 1/4 0.9(1.0) 0.01*

Al1 12k 0.1589(8) 0.318(2) 0.9220(8) 1.1(1.3) 0.05*

Al2 6h 0.567(1) 0.134(2) 1/4 1.4(1.6) 0.05*

Al3 4f 1/3 2/3 0.009(2) 1.0(1.2) 0.05*

Al4 2b 0 0 1/4 1.0(1.1) 0.01*

Fe1 6g 1/5 0 0 1.0(1.1) 0.01*

Fe2 2a 0 0 0 1.2(1.3) 0.04*

* - fixed parameter

Cell parameters, Å a = 8.7516(3) c = 9.2653(4)

RP 19.7

RWP 17.9

2 12.6

RB 7.86

RF 5.70

U3Co4+xAl12-x 8.7060(2) 9.2230(3)

U3Co4+xAl12-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

1/3 2/3 0.0084(2)

0 0 1/4

1/5 0 0

0 0 0

 

-UFeAl3

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

FeAl3Fe2Al5

FeAl2

UAl3

AlU

Fe

UFe

Al

L

L

UAl2

UFe2

FeAl

1

2

34

56

78

9

a

b

c

Al1

Al1

al4

Al1

Fe2

Al1

al4

Al1

Al1

PowderCell 2.0

a

b

c

Al1

al4

Al1

Al1

Fe1

Al2

Al1

U

Al1

Fe1

Fe1

al3

Al1

Al2

U

al3

Fe1

U

PowderCell 2.0

a

b

c

Al1

al3

Al2

U

U

Al1

Fe1

Al1

U

U

Al2

al3

Al1

PowderCell 2.0

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, μeff = 3.54(1) μB (considered 1U:1Fe:3Al)

μeff(U3+) = 3.62  μB or μeff(U4+) = 3.58  μB

U intermetallics → 2 – 3 μB

Fe contribution

’’

’

’’

’

R

’

Tf / [Tf log()]

Spin-glass: 0.004 - 0.03 (strong interactions between magnetic moments)

Superparamagnets:

0.25 - 0.35 (weak interactions between clusters)

U3Fe4Al12: 0.03 → true spin-glass

Arrhenius law

 = 0 exp(-TA/Tf)

Vogel-Fulcher law

 = 0 exp[-TA/(Tf-T0)]

0  1033 Hz and TA = Ea/kB = 535 K

Frequency dependence of the freezing temperature

0  1013 Hz

Conclusions

•U3Fe4Al12 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 2007-2008;