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195Pt and 119Sn Knight shifts of U3Pt3Sn4
ELSEVIER
Physica B 206 & 207 (1995) 479-481
195pt and ll9Sn Knight shifts of U3Pt3Sn 4 K. Kojima*, T. Takabatake, A. Harada, T. Hihara Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 724, Japan
Abstract
The WSPt and 119Sn Knight shifts in U3Pt3Sn4 have been measured in the temperature range 4.2-298K. They exhibit Curie-Weiss like behaviors above about 50 K and remain constant below about 10 K. This suggests that the deviation of x(T) from the modified Curie-Weiss law is an intrinsic property of U3Pt3Sn4.
Uranium ternary compounds U3T3X 4 (T = transition element and X = metalloid) provide a suitable class for investigating such physical properties as the Kondo effect and heavy fermion, because these properties are associated with the hybridization between the 5f electron and the conduction sp and d electron states, which depend on the combination of T and X atoms [1]. The 195pt and algSn Knight shifts in U3Pt3Sn 4 have been measured in a series of NMR studies of the hybridization effect on the U 5f electron states in U3T3X 4 [2,3]. U3PtaSn 4 crystallizes in a cubic YaAu3Sb4-type structure with a lattice constant of 9.675 A and is a moderately heavy electron compound with a linear specific heat coefficient of 3' = 94 m J / K z mol U at 0 K [1]. The electrical resistivity shows a T 2 dependence with a coefficient of 0.68 i~I~ c m / K 2 below 10 K, and the temperature dependence of the magnetic susceptibility follows a modified Curie-Weiss law x ( T ) = go + C / ( T - 0p) with Xo = 1.36 x 10 -3 emu/molU, / ~ e f f = l . 8 4 / ~ / U and 0 p = - 3 8 K between 50 and 300K. Below about 2 0 K , x(T) has a tendency towards saturation, and no magnetic ordering is observed down to 1.5 K [1]. The specimen of U3Pt3Sn 4 was prepared by arc
* Corresponding author.
melting the constituent metals under a purified argon atmosphere and was annealed in an evacuated silica capsule at 800°C for 10 days. The X-ray diffraction analysis showed that the sample is in the cubic Y3Au3Sb4-type phase. In the NMR measurements a fine powdered specimen was used, which was annealed at 400°C for 1 day before use, and the field-swept spectrum was obtained by using a phase-coherent pulsed NMR spectrometer and a boxcar integrator. The 1195n and 195pt NMR were measured at 18 and 9 M H z , respectively, in the temperature range 4 . 2 298 K. The line shapes of the 117'1195n NMR are asymmetric, similar to those in U3Ni3Sn 4 [2]. In the Y3Au3Sb4-type lattice of U3Pt3Sn 4 each Sn atom site has an axial symmetry along the [1 1 1] or its equivalent direction. The Knight shifts parallel and perpendicular to the symmetry axis, KII and K l , for the l198n NMR are shown as a function of temperature in Fig. 1. They are positive values and they increase in a Curie-Weiss like manner with lowering temperature down to about 50K, below which their increase becomes more gradual. Changes in the line shapes were not observed, indicating that no magnetic order occurred down to 4.2 K. This was consistent with the result of the specific heat measurement that no magnetic ordering is observed down to 1.5 K. The temperature dependence of the isotropic Knight shift gis o = (KII + 2K±)/3 is shown in Fig. 1 by the closed circles. Below about 50 K it follows Kiso(T)= K 0 +
0921-4526/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0921-4526(94)00496-X
K. Kojima et al. / Physica B 206 & 207 (1995) 479-481
480
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,
8L
u
U3Pt3Sn 4 l'gSn NMR
f=18.0o0Maz
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U3Pt3Sn 4 195pt NMR f= 9.000 MHz
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KIr ~, K± o
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150
250
260
0(
300
T (K)
510
2&o
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T (K) Fig. 3. Temperature dependence of the mSPt Knight shifts KII and K±.
Fig. 1. Temperature dependence of Kib K~ and K~,o= (KII + 2K~ )/3 for the X'gSnNMR. x(T) is also shown in the insert.
The Knight shifts KII and K 1 for the 195pt N M R are shown as a function of temperature in Fig. 3. The Knight shift is positive and anisotropic, reflecting an anisotropy of the local susceptibility at the Pt atom site. KII increased like a19Kii with decreasing temperature, but K± decreased gradually. The temperature dependence of Kis o and the Kis o v e r s u s X plot are shown in Fig. 4. The Kiso versus X plot is essentially linear, yielding A h f = + 9 . 7 k O e / / ~ . The anisotropic Knight shifts of g a n = (KII - K1)/3 for 195pt as well as 1195n are shown as a function of temperature in Fig. 5. The ll9Sn N M R Ki~o and Ka, are due to the polarization of conduction s and p electrons by 5f electrons, respectively, the value of Ka, being much smaller. On the other hand, gan is almost half of the K~so for the
CK/(T-- OK) with K o = 1.4%, C K = 2 9 4 % / K and 0x = - 3 6 K . The value of OK agrees with 0p = - 3 8 K obtained from x(T) [1]. The value of Kis o remains constant below about 10K. This suggests that the tendency of saturation of x ( T ) below about 20 K (see the insert of Fig. 1), is intrinsic in nature and a slight increase in x(T) at lower temperatures is the result of impurities. In Fig. 2 K~,o(T ) was plotted against x(T) with the temperature as an implicit parameter. The K~,o versus g plot is linear except in the lowest temperature range, where x(T) increases slightly. Using Ki~o = AhfxINtxB, where A , f is the transferred hyperfine coupling constant and N is A v o g a r d o ' s number, we obtain A , f = + 4 1 . 0 k O e / / x B, which is nearly equal to that in U3Ni3Sn 4 [2]. The line shape of the X 9 5 p t ( l = l / 2 ) N M R is asymmetric, similar to those of the 117'1195n NMR.
X (lO3ernu/mol - U ) ~0 / 6 5
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% (10"3emu/mol-U ) 4 6
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UaPt3Sn 4 9Sn NMR f=18.000MHz •
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300
5'0
100
1,50
200
250
300
T (K) Fig. 4. Temperature dependence of the isotropic Knight shift K~so and the K.,o versus g plot for the '95pt NMR.
K. Kojima et al. / Physica B 206 & 207 (1995) 479-481
lower temperatures [4,5]. No observations of such a deviation in U3Pt3Sn 4 suggests that the transferred hyperfine coupling is only weakly dependent on the moment reduction in this compound [5] and (or) the temperature in this measurement was not low enough to induce such a non-linear K versus X relation. In U3Ni3Sn 4 the 1~98n nuclear relaxation results showed that the 5f electrons were delocalized below liquid He temperature [2]. Measurements of the nuclear spinlattice relaxation times of tl9Sn and 195pt are now in progress in order to obtain further microscopic magnetic properties of U3Pt3Sn 4.
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481
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T (K)
Fig. 5. Temperature dependence of the anisotropic parts of the 195pt and 1~9Sn Knight shifts K~n = (Kfl - K~)/3. 195pt NMR, suggesting that d electrons play an important role in the hyperfine interaction as in the 63Cu N M R of U3Cu3Sn 4 [3]. The 119Sn and 195pt Knight shifts in U3Pt3Sn 4 exhibit a Curie-Weiss like behavior above about 50 K and have a tendency to saturation at lower temperatures. This suggests that the character of the 5f electrons changes from localized to heavy fermion with decreasing temperature. In many 4f heavy fermion compounds it was observed that the K versus X plot exhibits a deviation from its linear relation at
References
[1] T. Takabatake, S. Miyata, H, Fujii, Y. Aoki, T. Suzuki, T. Fujita, J. Sakurai and T. Hiraoka, J. Phys. Soc. Japan 59 (1990) 4412. [2] K. Kojima, Y. Hukuda, S. Miyata, T. Takabatake, H. Fujii and T. Hihara, J. Phys. Soc. Japan 60 (1991) 2546. [3] K. Kojima, Y. Hukuda, S. Miyata, T. Takabatake, H. Fujii and T. Hihara, J. Magn. Magn. Mater. 104-107 (1992) 49. [4] D.E. MacLaughlin, F.R. de Boer, J. Bijvoet, P.F. de Ch~tel and W.C.M. Mattens, J. Appl. Phys. 50 (1979) 2094. [5] D.E. MacLaughlin, Hyperfine Interactions 49 (1989) 43.
Physica B 206 & 207 (1995) 479-481
195pt and ll9Sn Knight shifts of U3Pt3Sn 4 K. Kojima*, T. Takabatake, A. Harada, T. Hihara Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 724, Japan
Abstract
The WSPt and 119Sn Knight shifts in U3Pt3Sn4 have been measured in the temperature range 4.2-298K. They exhibit Curie-Weiss like behaviors above about 50 K and remain constant below about 10 K. This suggests that the deviation of x(T) from the modified Curie-Weiss law is an intrinsic property of U3Pt3Sn4.
Uranium ternary compounds U3T3X 4 (T = transition element and X = metalloid) provide a suitable class for investigating such physical properties as the Kondo effect and heavy fermion, because these properties are associated with the hybridization between the 5f electron and the conduction sp and d electron states, which depend on the combination of T and X atoms [1]. The 195pt and algSn Knight shifts in U3Pt3Sn 4 have been measured in a series of NMR studies of the hybridization effect on the U 5f electron states in U3T3X 4 [2,3]. U3PtaSn 4 crystallizes in a cubic YaAu3Sb4-type structure with a lattice constant of 9.675 A and is a moderately heavy electron compound with a linear specific heat coefficient of 3' = 94 m J / K z mol U at 0 K [1]. The electrical resistivity shows a T 2 dependence with a coefficient of 0.68 i~I~ c m / K 2 below 10 K, and the temperature dependence of the magnetic susceptibility follows a modified Curie-Weiss law x ( T ) = go + C / ( T - 0p) with Xo = 1.36 x 10 -3 emu/molU, / ~ e f f = l . 8 4 / ~ / U and 0 p = - 3 8 K between 50 and 300K. Below about 2 0 K , x(T) has a tendency towards saturation, and no magnetic ordering is observed down to 1.5 K [1]. The specimen of U3Pt3Sn 4 was prepared by arc
* Corresponding author.
melting the constituent metals under a purified argon atmosphere and was annealed in an evacuated silica capsule at 800°C for 10 days. The X-ray diffraction analysis showed that the sample is in the cubic Y3Au3Sb4-type phase. In the NMR measurements a fine powdered specimen was used, which was annealed at 400°C for 1 day before use, and the field-swept spectrum was obtained by using a phase-coherent pulsed NMR spectrometer and a boxcar integrator. The 1195n and 195pt NMR were measured at 18 and 9 M H z , respectively, in the temperature range 4 . 2 298 K. The line shapes of the 117'1195n NMR are asymmetric, similar to those in U3Ni3Sn 4 [2]. In the Y3Au3Sb4-type lattice of U3Pt3Sn 4 each Sn atom site has an axial symmetry along the [1 1 1] or its equivalent direction. The Knight shifts parallel and perpendicular to the symmetry axis, KII and K l , for the l198n NMR are shown as a function of temperature in Fig. 1. They are positive values and they increase in a Curie-Weiss like manner with lowering temperature down to about 50K, below which their increase becomes more gradual. Changes in the line shapes were not observed, indicating that no magnetic order occurred down to 4.2 K. This was consistent with the result of the specific heat measurement that no magnetic ordering is observed down to 1.5 K. The temperature dependence of the isotropic Knight shift gis o = (KII + 2K±)/3 is shown in Fig. 1 by the closed circles. Below about 50 K it follows Kiso(T)= K 0 +
0921-4526/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0921-4526(94)00496-X
K. Kojima et al. / Physica B 206 & 207 (1995) 479-481
480
lO
,
8L
u
U3Pt3Sn 4 l'gSn NMR
f=18.0o0Maz
| oo
6 I-'.. °,:~
/ '¢" 4~-
,
,
~" ~ 8~.'
{
E 4L
~=
,~%% o~ %~*~*~ ~ o o
,
'
'
~ ~
...... ol
200 T (K)
i
U3Pt3Sn 4 195pt NMR f= 9.000 MHz
°o 5
J
I
i
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7
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Kis° = ( K / ! + 2 K ± ) / 3
0~
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EDO0
KIr ~, K± o
2
/
I
4
150
250
260
0(
300
T (K)
510
2&o
1DO
300
T (K) Fig. 3. Temperature dependence of the mSPt Knight shifts KII and K±.
Fig. 1. Temperature dependence of Kib K~ and K~,o= (KII + 2K~ )/3 for the X'gSnNMR. x(T) is also shown in the insert.
The Knight shifts KII and K 1 for the 195pt N M R are shown as a function of temperature in Fig. 3. The Knight shift is positive and anisotropic, reflecting an anisotropy of the local susceptibility at the Pt atom site. KII increased like a19Kii with decreasing temperature, but K± decreased gradually. The temperature dependence of Kis o and the Kis o v e r s u s X plot are shown in Fig. 4. The Kiso versus X plot is essentially linear, yielding A h f = + 9 . 7 k O e / / ~ . The anisotropic Knight shifts of g a n = (KII - K1)/3 for 195pt as well as 1195n are shown as a function of temperature in Fig. 5. The ll9Sn N M R Ki~o and Ka, are due to the polarization of conduction s and p electrons by 5f electrons, respectively, the value of Ka, being much smaller. On the other hand, gan is almost half of the K~so for the
CK/(T-- OK) with K o = 1.4%, C K = 2 9 4 % / K and 0x = - 3 6 K . The value of OK agrees with 0p = - 3 8 K obtained from x(T) [1]. The value of Kis o remains constant below about 10K. This suggests that the tendency of saturation of x ( T ) below about 20 K (see the insert of Fig. 1), is intrinsic in nature and a slight increase in x(T) at lower temperatures is the result of impurities. In Fig. 2 K~,o(T ) was plotted against x(T) with the temperature as an implicit parameter. The K~,o versus g plot is linear except in the lowest temperature range, where x(T) increases slightly. Using Ki~o = AhfxINtxB, where A , f is the transferred hyperfine coupling constant and N is A v o g a r d o ' s number, we obtain A , f = + 4 1 . 0 k O e / / x B, which is nearly equal to that in U3Ni3Sn 4 [2]. The line shape of the X 9 5 p t ( l = l / 2 ) N M R is asymmetric, similar to those of the 117'1195n NMR.
X (lO3ernu/mol - U ) ~0 / 6 5
%%° % " ,,
4
3.51
% (10"3emu/mol-U ) 4 6
2
UaPt3Sn 4 9Sn NMR f=18.000MHz •
•
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2
4
6
8
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I
i
i
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._8
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UaPtaSn4 195pt NMR f= 9.000 MHz
1.0 j~.~
•
•
0.5
. .,...
..,,-"
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0"00
. ...,-.
s'o
160
40
260
2;0
T (K) Fig. 2. The K~o versus g plot for the U9Sn NMR.
300
5'0
100
1,50
200
250
300
T (K) Fig. 4. Temperature dependence of the isotropic Knight shift K~so and the K.,o versus g plot for the '95pt NMR.
K. Kojima et al. / Physica B 206 & 207 (1995) 479-481
lower temperatures [4,5]. No observations of such a deviation in U3Pt3Sn 4 suggests that the transferred hyperfine coupling is only weakly dependent on the moment reduction in this compound [5] and (or) the temperature in this measurement was not low enough to induce such a non-linear K versus X relation. In U3Ni3Sn 4 the 1~98n nuclear relaxation results showed that the 5f electrons were delocalized below liquid He temperature [2]. Measurements of the nuclear spinlattice relaxation times of tl9Sn and 195pt are now in progress in order to obtain further microscopic magnetic properties of U3Pt3Sn 4.
2.0
1.5
~D DD D
D 19Spt o ~gSn
OD
o~
D
1.0
DD Do D
0.5
D O
°°°°°(3°°°°O(000 0.0
510
1 (30
D
O
0 0 0 0 0 0D D
1;0
260
OD 250
481
300
T (K)
Fig. 5. Temperature dependence of the anisotropic parts of the 195pt and 1~9Sn Knight shifts K~n = (Kfl - K~)/3. 195pt NMR, suggesting that d electrons play an important role in the hyperfine interaction as in the 63Cu N M R of U3Cu3Sn 4 [3]. The 119Sn and 195pt Knight shifts in U3Pt3Sn 4 exhibit a Curie-Weiss like behavior above about 50 K and have a tendency to saturation at lower temperatures. This suggests that the character of the 5f electrons changes from localized to heavy fermion with decreasing temperature. In many 4f heavy fermion compounds it was observed that the K versus X plot exhibits a deviation from its linear relation at
References
[1] T. Takabatake, S. Miyata, H, Fujii, Y. Aoki, T. Suzuki, T. Fujita, J. Sakurai and T. Hiraoka, J. Phys. Soc. Japan 59 (1990) 4412. [2] K. Kojima, Y. Hukuda, S. Miyata, T. Takabatake, H. Fujii and T. Hihara, J. Phys. Soc. Japan 60 (1991) 2546. [3] K. Kojima, Y. Hukuda, S. Miyata, T. Takabatake, H. Fujii and T. Hihara, J. Magn. Magn. Mater. 104-107 (1992) 49. [4] D.E. MacLaughlin, F.R. de Boer, J. Bijvoet, P.F. de Ch~tel and W.C.M. Mattens, J. Appl. Phys. 50 (1979) 2094. [5] D.E. MacLaughlin, Hyperfine Interactions 49 (1989) 43.