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Magnetism of ternary compounds U-T-Ga (T = transition elements)
Journal of Magnetism and Magnetic Materials 104-107 (1992) 57-59 North-Holland
AI I"
Magnetism of ternary compounds U - T - G a (T = transition elements) S. N o g u c h i
a n d K. O k u d a
College of Engineering, Unicersityof Osaka Prefecture, Sakai, Osaka 591, Japan Magnetic properties of ternary uranium compounds UTGa 5 (T = Co and Ni) have been investigated by magnetization and electric resistivity measurements. An antiferromagnetic-like ordering was found in the compound UNiGa 5 at TM = 85.5 K, where the temperature dependence of the magnetization and resistivity shows a peak and a small hump, respectively. In the compound UCoGa 5 the resistance has a minimum near 25 K.
In recent years, a great deal of interest has been shown in the electronic and magnetic properties of various uranium compounds. Ternary uranium gallides U T G a 5 (T = iron group) crystallize in the H o C o G a 5type structure, combining structural units of A u C u 3and PtHg2-type [1]. In order to investigate the magnetic properties, we synthesized the compounds U T G a 5 (T = Co and Ni) and measured the magnetization and electric resistivity. The samples U T G a 5 (T = Co and Ni) were synthesized by arc-melting the constituent metallic elements in an argon atmosphere. Subsequently, they were 1 wrapped with a Ta foil, sealed into a quartz tube with 3 Ar atmosphere and then annealed at 870 ° C for 7 days. By E P M A (electron probe micro analysis) and the X-ray powder diffraction measurements the samples obtained were found to be a stoichiometric single phase of U T G a s , which belongs to the H o C o G a 5 type structure with a tetragonal symmetry of P4/mmm-Dalh [1] as shown in fig. 1. The diffraction data were analyzed by the Rietveld method as shown in fig. 2. The lattice constants were refined to beo a = 4.233 A, c = 6.723 ,~ for U C o G a 5 and a = 4.231 A, c = 6.774 A for U N i G a 5. In the structure, the U and T atoms are located at (la) and (lb) positions, respectively. The Ga atoms are located at (lc) and (4i) positions. The fractional coordinates of Ga(4i) site were determined to be (0, ½, 0.3048) and (0, l , 0.3129) for U C o G a 5 and U N i G a s , respectively. T e m p e r a t u r e dependence of the magnetization M was measured by using a standard Faraday type magnetometer (Cahn-2000) in a magnetic field H = 7.38 kOe. The results ( M / H ) are shown in fig. 3. The magnetization of U C o G a 5 slightly decreases with decreasing temperature down to = 100 K, followed by the C u r i e - W e i s s law below 100 K. In the compound U N i G a 5 the magnetization gradually increases with decreasing temperature down to 85.5 K, showing a peak at T M = 85.5 K, followed by the C u r i e - W e i s s law below 40 K. The peak in U N i G a 5 suggests an antifer-
romagnetic-like ordering. These temperature dependences in the high temperature range suggest that the 5f electrons are rather itinerant than localized in both compounds. A C u r i e - W e i s s relation was fitted, X = C/(T-O)+xo in the low temperature region for both compounds. The parameters obtained were C = 2.73 and 9.77 x 10 -3 K e m u / m o l , O = - 2 . 8 and - 8 . 3 K, and X 0 = 0 . 8 3 and 1 . 1 2 x 10 _3 e m u / m o l for U C o G a 5 and U N i G a 5, respectively. The effective moments ~eff = 0.15 and 0.28p~B/f.u. for U C o G a 5 and U N i G a s , respectively, are estimated from the Curie constant. The origin of the C u r i e - W e i s s behavior is not clear. The temperature dependence of the electrical resistivity p was measured by a standard four terminal method in a temperature range from 4.2 to 300 K. The results are shown in fig. 4. The resistivity of U C o G a 5
¢
° a
©Co • Go
Fig. 1. Crystal structure of UCoGa 5. The inferatomic distance du_u, dtJ_Ga and du_co are 4.233, 2.946 and 3.361 ,~, respectively.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
S. Noguchi, K. Okuda / Magnetism of ternary_ compounds U-T-Ga
58
5. OR 4.
SR
o
~
~,
~
~
4. OK
233
a
=
4.
c
=
6.723
A
3. SX u) 3.0~ c
2
o o
o o
1. D .;~. r , o
1.0~
0 0 ~ 0
0
~-l~.
0
rxa
~..
.~'
~
;
~
~
.
.
O. S1
0,01
I 10[ 0
i
i
1
I
II
1
I
20'.0
I
II I li
,o'. o
30'.0
i
II
so'.o
28
i
i
II III llllilllllilN so'.o
7o:0
nnlfllillfllll
W.o
W.o
u 524~
Fig. 2. X-ray diffraction pattern of U C o G a 5. S t e p - s c a n n e d intensity data are shown by dots• T h e solid line is the Rietveld r e f i n e m e n t pattern• T h e R-factors are Rwp = 11.8%, Rp = 9.2%, R] = 10.8% and R F = 8.3%, w h e r e R's follow the definition of Y o u n g et al. [2]• I
I
I
I
[
I
I
l
I
I
2L
i
,
i
H = 7.38
i
[kOe]
o
E
,-.t
E
? O
UCoGa 5
0
I
0
I
I
I
I t i 100 TEMPERATURE
t
I
I 2OO [KI
I
I
I
00
Fig. 3. T e m p e r a t u r e d e p e n d e n c e of the m a g n e t i z a t i o n M, divided by applied field H = 7.38 k O e for U C o G a 5 and U N i G a 5. A clear p e a k is s e e n at T M = 85.5 K in the c o m p o u n d U N i G a 5.
S. Noguchi, K. Okuda /Magnetism of ternary compounds U-T-Ga 3001
I
~--
,
l
I
l
F "'A
f |
....
5
I
I
,
I
~"
I
,
r
UCoGa5
59
/
[
",.j_
I
,
10
,
•
20
I
,
/
50
a 5
100 --"-'-----"~
I
0
i
j~
I
i
I
i
I
I
J
I
100 200 T E M P E R A T U R E [K]
I
1
l
l
300
Fig. 4. Temperature dependence of the resistivity for UCoGa 5 and UNiGa s. A small hump is seen just below T M in the compound UNiGa 5. Inset shows the low temperature part for UCoGa 5 on a larger scale. A clear log T dependence is seen below 20 K. shows a minimum near 25 K, followed by a logarithmic temperature dependence down to 8 K. Below the temperature it deviates downwards from the log T-dependence as shown in the inset of the figure. In the compound U N i G a 5 the resistivity decreases smoothly down to T M, where it shows a small hump, followed by a rapid drop with decreasing temperature. The residual resistivity is 7.7 Ixf~ cm. No hysteresis was found in the resistivity around T M. Specific heat measurements of the compounds were done by Noguchi et al. [3]. An upturn of the specific heat for U C o G a 5 was observed from 2 K down to 1.5 K, which may be a tail of a magnetic transition occurring at the temperature below 1.5 K. In the compound U N i G a 5 a peak in the specific heat was found at the temperature T M. C / T vs. T 2 plots did not follow a straight line but had a positive curvature at temperatures below 20 K. The electronic specific heat coefficient 3, was found to be = 10 and 30 m J / m o l K 2 for U C o G a 5 and U N i G a s , respectively [3]. The ratio of
X/Xcal, where Xcal is the value calculated from the value 3' by using the free electron model, is 2.0-2.5 for both compounds. In conclusion, both compounds have rather itinerant character with the large magnetic exchange enhancement. This work is partially supported by the project of priority area for the physics on actinide compounds, a Grant-in Aid for Scientific Research from the Ministry of Education, Science and Culture in Japan. References
[1] Y.N. Grin, P. Rogl and K. Hiebl, J. Less-Common Met. 121 (1986) 497. [2] R.A. Young, E. Prince and R.A. Sparks, J. Appl. Crystallogr. 15 (1982) 357. [3] S. Noguchi, H. Suzuki, K. Okuda, T. Nishioka and M. Kontani, in preparation for publication.
AI I"
Magnetism of ternary compounds U - T - G a (T = transition elements) S. N o g u c h i
a n d K. O k u d a
College of Engineering, Unicersityof Osaka Prefecture, Sakai, Osaka 591, Japan Magnetic properties of ternary uranium compounds UTGa 5 (T = Co and Ni) have been investigated by magnetization and electric resistivity measurements. An antiferromagnetic-like ordering was found in the compound UNiGa 5 at TM = 85.5 K, where the temperature dependence of the magnetization and resistivity shows a peak and a small hump, respectively. In the compound UCoGa 5 the resistance has a minimum near 25 K.
In recent years, a great deal of interest has been shown in the electronic and magnetic properties of various uranium compounds. Ternary uranium gallides U T G a 5 (T = iron group) crystallize in the H o C o G a 5type structure, combining structural units of A u C u 3and PtHg2-type [1]. In order to investigate the magnetic properties, we synthesized the compounds U T G a 5 (T = Co and Ni) and measured the magnetization and electric resistivity. The samples U T G a 5 (T = Co and Ni) were synthesized by arc-melting the constituent metallic elements in an argon atmosphere. Subsequently, they were 1 wrapped with a Ta foil, sealed into a quartz tube with 3 Ar atmosphere and then annealed at 870 ° C for 7 days. By E P M A (electron probe micro analysis) and the X-ray powder diffraction measurements the samples obtained were found to be a stoichiometric single phase of U T G a s , which belongs to the H o C o G a 5 type structure with a tetragonal symmetry of P4/mmm-Dalh [1] as shown in fig. 1. The diffraction data were analyzed by the Rietveld method as shown in fig. 2. The lattice constants were refined to beo a = 4.233 A, c = 6.723 ,~ for U C o G a 5 and a = 4.231 A, c = 6.774 A for U N i G a 5. In the structure, the U and T atoms are located at (la) and (lb) positions, respectively. The Ga atoms are located at (lc) and (4i) positions. The fractional coordinates of Ga(4i) site were determined to be (0, ½, 0.3048) and (0, l , 0.3129) for U C o G a 5 and U N i G a s , respectively. T e m p e r a t u r e dependence of the magnetization M was measured by using a standard Faraday type magnetometer (Cahn-2000) in a magnetic field H = 7.38 kOe. The results ( M / H ) are shown in fig. 3. The magnetization of U C o G a 5 slightly decreases with decreasing temperature down to = 100 K, followed by the C u r i e - W e i s s law below 100 K. In the compound U N i G a 5 the magnetization gradually increases with decreasing temperature down to 85.5 K, showing a peak at T M = 85.5 K, followed by the C u r i e - W e i s s law below 40 K. The peak in U N i G a 5 suggests an antifer-
romagnetic-like ordering. These temperature dependences in the high temperature range suggest that the 5f electrons are rather itinerant than localized in both compounds. A C u r i e - W e i s s relation was fitted, X = C/(T-O)+xo in the low temperature region for both compounds. The parameters obtained were C = 2.73 and 9.77 x 10 -3 K e m u / m o l , O = - 2 . 8 and - 8 . 3 K, and X 0 = 0 . 8 3 and 1 . 1 2 x 10 _3 e m u / m o l for U C o G a 5 and U N i G a 5, respectively. The effective moments ~eff = 0.15 and 0.28p~B/f.u. for U C o G a 5 and U N i G a s , respectively, are estimated from the Curie constant. The origin of the C u r i e - W e i s s behavior is not clear. The temperature dependence of the electrical resistivity p was measured by a standard four terminal method in a temperature range from 4.2 to 300 K. The results are shown in fig. 4. The resistivity of U C o G a 5
¢
° a
©Co • Go
Fig. 1. Crystal structure of UCoGa 5. The inferatomic distance du_u, dtJ_Ga and du_co are 4.233, 2.946 and 3.361 ,~, respectively.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
S. Noguchi, K. Okuda / Magnetism of ternary_ compounds U-T-Ga
58
5. OR 4.
SR
o
~
~,
~
~
4. OK
233
a
=
4.
c
=
6.723
A
3. SX u) 3.0~ c
2
o o
o o
1. D .;~. r , o
1.0~
0 0 ~ 0
0
~-l~.
0
rxa
~..
.~'
~
;
~
~
.
.
O. S1
0,01
I 10[ 0
i
i
1
I
II
1
I
20'.0
I
II I li
,o'. o
30'.0
i
II
so'.o
28
i
i
II III llllilllllilN so'.o
7o:0
nnlfllillfllll
W.o
W.o
u 524~
Fig. 2. X-ray diffraction pattern of U C o G a 5. S t e p - s c a n n e d intensity data are shown by dots• T h e solid line is the Rietveld r e f i n e m e n t pattern• T h e R-factors are Rwp = 11.8%, Rp = 9.2%, R] = 10.8% and R F = 8.3%, w h e r e R's follow the definition of Y o u n g et al. [2]• I
I
I
I
[
I
I
l
I
I
2L
i
,
i
H = 7.38
i
[kOe]
o
E
,-.t
E
? O
UCoGa 5
0
I
0
I
I
I
I t i 100 TEMPERATURE
t
I
I 2OO [KI
I
I
I
00
Fig. 3. T e m p e r a t u r e d e p e n d e n c e of the m a g n e t i z a t i o n M, divided by applied field H = 7.38 k O e for U C o G a 5 and U N i G a 5. A clear p e a k is s e e n at T M = 85.5 K in the c o m p o u n d U N i G a 5.
S. Noguchi, K. Okuda /Magnetism of ternary compounds U-T-Ga 3001
I
~--
,
l
I
l
F "'A
f |
....
5
I
I
,
I
~"
I
,
r
UCoGa5
59
/
[
",.j_
I
,
10
,
•
20
I
,
/
50
a 5
100 --"-'-----"~
I
0
i
j~
I
i
I
i
I
I
J
I
100 200 T E M P E R A T U R E [K]
I
1
l
l
300
Fig. 4. Temperature dependence of the resistivity for UCoGa 5 and UNiGa s. A small hump is seen just below T M in the compound UNiGa 5. Inset shows the low temperature part for UCoGa 5 on a larger scale. A clear log T dependence is seen below 20 K. shows a minimum near 25 K, followed by a logarithmic temperature dependence down to 8 K. Below the temperature it deviates downwards from the log T-dependence as shown in the inset of the figure. In the compound U N i G a 5 the resistivity decreases smoothly down to T M, where it shows a small hump, followed by a rapid drop with decreasing temperature. The residual resistivity is 7.7 Ixf~ cm. No hysteresis was found in the resistivity around T M. Specific heat measurements of the compounds were done by Noguchi et al. [3]. An upturn of the specific heat for U C o G a 5 was observed from 2 K down to 1.5 K, which may be a tail of a magnetic transition occurring at the temperature below 1.5 K. In the compound U N i G a 5 a peak in the specific heat was found at the temperature T M. C / T vs. T 2 plots did not follow a straight line but had a positive curvature at temperatures below 20 K. The electronic specific heat coefficient 3, was found to be = 10 and 30 m J / m o l K 2 for U C o G a 5 and U N i G a s , respectively [3]. The ratio of
X/Xcal, where Xcal is the value calculated from the value 3' by using the free electron model, is 2.0-2.5 for both compounds. In conclusion, both compounds have rather itinerant character with the large magnetic exchange enhancement. This work is partially supported by the project of priority area for the physics on actinide compounds, a Grant-in Aid for Scientific Research from the Ministry of Education, Science and Culture in Japan. References
[1] Y.N. Grin, P. Rogl and K. Hiebl, J. Less-Common Met. 121 (1986) 497. [2] R.A. Young, E. Prince and R.A. Sparks, J. Appl. Crystallogr. 15 (1982) 357. [3] S. Noguchi, H. Suzuki, K. Okuda, T. Nishioka and M. Kontani, in preparation for publication.