spin glass behaviour in a new ternary intermetallic, u 3 fe 4+x al 12-x a.p. gonçalves 1, o....
TRANSCRIPT
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;