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Physical properties of antiferromagnetic ternary compound SmPd2Al3
PHYSICA
Physica B 186-188 (1993) 661-663 North-Holland
Physical properties of antiferromagnetic ternary compound SmPd2A13 H. Kitazawa a, A. Mori b, S. Takano b, T. Yamadaya b, A. Matsushita c, and T. M a t s u m o t o c "The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan bYokohama City University, Kanazawa-ku, Yokohama 236, Japan ~National Research Institute for Metals, Tokyo 153, Japan Measurements of electrical resistivity, magnetic susceptibility and specific heat have been performed on a new ternary compound SmPd2AI3. The results indicate that the valence of Sm ions is almost trivalent and that SmPd2AI3 has a complicated magnetic phase diagram below 12 K.
Recently, the project of development of new ternary rare earth and actinide compounds, which show exotic physical properties, led to the discovery of new ternary compounds RPd2A13 (R: rare earth and actinide elements) with the hexagonal PrNi~A13 type structure. Among them, it was found that UPd2AI 3 and CePd2A13 were interesting substances. The former is a new heavy-fermion superconductor ( T c = 2 K , TN = 14 K) [1] and the latter is a new heavy fermion substance which exhibits an antiferromagnetic ordering below T N = 2.8 K [2]. In this article, we present the first results of the magnetic, transport and thermal properties of SmPd2AI 3 with a homologous structure by measurement of magnetic susceptibility, electrical resistivity and specific heat. Polycrystalline samples of SmPd2A13 were synthesized by arc-melting the stoichiometric mixtures of 3N-Sm, 3N-Pd and 5N-AI in an argon atmosphere. As-cast samples were annealed at 900°C for 120 h in a high vacuum. The pattern of X-ray powder diffraction agrees well with a calculated diffraction pattern for the hexagonal PrNi2Al3-type structure. The lattice constants were determined to be a = 5.41310(5)A and c = 4.19971(6) A by the whole-powder-pattern-decomposition (WPPD) method [3]. The volume of already observed homologous compounds RPd2A13 (R = La, Ce [2] and Sm) monotonously decreases with the radius of R 3+ ion. It suggests that the valence of Sm
ions is almost trivalent. The electrical resistivity was measured by the conventional four-terminal DC method in the temperature range 1.7-300 K. The specific heat between 1.5 and 4 0 K was measured using the conventional adiabatic technique. The susceptibility, X, and magnetization, M, in the field range 0 . 1 - 4 T and in the temperature range 1.7-300K were measured by a SQUID magnetometer (CCL Co.). The powdered and parallelpiped samples were used for the measurements of X and M, respectively. The overall temperature dependence of the electrical resistivity in SmPd2A13 exhibits metallic behavior as in the case of nonmagnetic LaPd2AI 3 as shown in fig. 1. However, a cusp is clearly observed at 12 K in SmPd2A13. This cusp suggests the presence of mag-
Correspondence to: H. Kitazawa, The Institute of Physical and Chemical Research (RIKEN) Wako, Saitama 351-01, Japan.
Fig. 1. The electrical resistivity R(T) of SmPd2A13 and LaPd2Al3 as a function of temperature. The inset shows p(T) of SmPd2A13 on an enlarged scale around the anomaly.
200
I
40
T1
~35
L,,,,~,~,~ ~°o"~
oE 150
SmPd 2AI3
> 100 ._~
rr 50
0
. . . .
0
0921-4526/93/$06.00 © 1993- Elsevier Science Publishers B.V. All rights reserved
i
. . . .
50
i
.
.
.
.
i
. . . .
i
. . . .
100 150 200 Temperature ( K )
i
. . . .
250
300
662
H. Kitazawa et al. / Physical properties of SmPd:AI,
netic ordering below T 1 = 12 K and is discussed later. Figure 2 shows the temperature dependence of the specific heat, C(T), of SmPd2A13 and LaPd2A13. Two large peaks of the A-type were clearly observed at 12 K (T1) and 4.3K ( T 2 ) . Moreover, a small shoulder, which is located in the vicinity of the large peak at 4.3 K, is visible at 4.0 K (T3) as shown in the inset. Therefore, there are three phase transition temperatures, T t, T~ and T3, above 1.5 K under zero field. The magnetic part of specific heat, C m, for SmPd2A13 was derived by subtracting the specific heat of the nonmagnetic LaPd2AI 3 as a phonon contribution. When the magnetic contribution to the entropy is neglected below 1.65 K, the value of the magnetic entropy reaches to 0 . 8 9 R l n 2 at 20K. A J = 5 / 2 multiplet of Sm 3+, which is sixfold degenerate, splits into three doublets by the hexagonal crystalline electrical field (CEF). The value of the obtained entropy indicates that the ground state is doublet. The Schottky anomaly is not observed up to 40 K in comparison with CePd2AI3, which has a maximum at 14 K [4]. At least, it is suggested that the first excited state is apart from the ground state by the order of 100K in SmPd2AI ~. Thus, this system is clearly influenced by the CEF effect. The susceptibility of LaPd2A13, which is paramagnetic, is found to be 6.0 × 10 5 emu/mol at room temperature and almost temperature independent. The electrical specific heat coefficient, 7, of LaPd:AI 3 was found to be 8 . 8 m J / m o l K 2 from the C / T versus T 2 plot. The 4f-spin susceptibility, XSm--XL~, in SmPd2AI 3 was estimated from the difference between Xsm and XL,, where XSm and XL, are the susceptibilities of SmPd2AI 3 and LaPdzAI 3, respectively. The temperature dependence of Xsm- XL~ between 1.7 and 300 K under the magnetic field of 0.1 T is shown in Fig. 3(a). It is clearly found that three peaks observed 35
8
30
.=Sm
25
~e" i,
o
E
20
/
°
R = La 2
15
O
T2
lO
T1 v
~
0
5
10
o°
o 3
4
\oo.°-"
1 5
I6
o°. oo:.
oo-
o~:." oO.~."
15 20 25 30 Temperature ( K )
"
R = La
35
40
Fig. 2. Temperature dependence of the specific heat of SmPd2AI3 and LaPd2AI3 between 1.5 and 40 K.
0.06
1200 SmPd 2 AI 3 i H=O.IT , . . . . ~ ~ " ' ~
0.05
1000
0.04
800
0.03
600 2z
;~ 0.02
400 /
Sm3*
(a)
0.01
0.00
200
50
250
20O r308
Temperature ( K )
0.06 5 E
2
•go%131"2 T
0.05
110oo
(b) ] t800 E
SmPd2 a13
0.04
H:O.1T
T,
0.03
tooo
E 0.02
o*
0.01 0.00
0 ,4 , .
8 e
-
.e~el ; o ~ . . T(K)
"
16o~28
]200 --
Fig. 3. (a) Temperature dependence of 4f-spin susceptibility, XSm--Xt.~, (O) and its inverse, 1/()(Sm-XL,) (O) in SmPd2AI3 under H = 0.1 T. (b) XSm--XL, and 1/(Xs,, X,~) as a function of temperature are shown on an enlarged scale at low temperatures. in C(T) are attributed to the magnetic phase transition and correspond to the anomalies of X as shown in fig. 3(b). With decreasing temperature, X changes as follows: (1) steep increase from 12K (T,); (2) two maxima at 10 and 4.3 K (T2) and (3) steep increase again from 4.0K (T3). The solid curve exhibits the contribution of free Sm 3÷ ions whose 4f state has an energy separation of 1500K between the ground J = 5/2 and the first excited J = 7/2 muitiplets. The temperature dependence of 1/(Xs m --XL,) indicates that the valence of Sm is almost trivalent rather than divalent. The deviation from the solid curve may be explained by the CEF effect and the exchange interaction. Figure 4 shows the magnetization, M ( T ) , as a function of temperature under the various magnetic fields. Although T~ and T 2 a r e not so influenced by field up to 4 T, T 3 shifts to the lower temperature with increasing field. The maximum observed at 10 K under 0.1 T smears out with increasing field. On the other hand, the other faint maximum observed around T2 under
H. Kitazawa et al. / Physical properties of SmPd,AI 3 0.030 "~"
0.025
4 T -..
,'"
~'~ ~ ~.=
0,020
3 T
•"
0.015
2T
,~
~
• • mm =" =
v
.-~
served in T < T 3 is too small, it is not obvious whether this is attributed to the intrinsic ferromagnetic component or the impurity. In summary, the measurements of lattice constants and X reveal that the valence of Sm is almost trivalent in SmPd2Al 3. This compound clearly has a complicated magnetic phase diagram and is influenced by the CEF effect. Further measurements to clarify the magnetic properties of SmPd2A13 are in progress.
S m P d 2AI 3
•,,,.
== •
•
=
===
=
=
==
0.01 0 0.5 T " ~ 0.005 0.1 T
° °~o o o o •.
~'°"
C~=OOq~q~
. . . . . . .
0.000 0
"'e
"
O,OO. CIOOOOOO O ~
5
D
o
°
" ° ° l
o DD
O O?.O
10
663
° Oo D n D " e I = . p~,,~.O
15
The authors are grateful to Mr. Y. Iimura for X-ray analysis.
Temperature ( K )
Fig. 4. Magnetization of SmPd2A13 as a function of temperature under the various magnetic fields.
References
0.1 T develops into a prominent broad peak with increasing field. When field above 2 T is applied, the amplitude of magnetization at T2 is greater than that below T 3. The field dependence of M at 1.7 K reveals a small remanence of about 0.003k%/Sm. However, a hysteresis phenomena and remanence were not observed in the M ( H ) curve with constant temperature of 4.2 K. At least, it is thought that the magnetic moments antiferromagnetically order in the narrow region between T 2 and T 3. Since the remanence ob-
[1] C. Geibel, C. Schank, S. Thies, H. Kitazawa, C.D. Bred|, A. B6hm, M. Rau, A. Grauel, R. Caspary, R. Helfrich, U. Ahlheim, G. Weber and F. Steglich, Z. Phys. B 84 (1991) 1. [2] H. Kitazawa, C. Schank, S. Thies, B. Seidel, C. Geibel and F. Steglich, J. Phys. Soc. Jpn. 61 (1992) 1461. [3] H. Toraya, J. Appl. Cryst. 19 (1986) 440. [4] H. Kitazawa, A. Mori, S. Takano, T. Yamadaya, A. Matsushita, T. Matsumoto, N. Sato, T. Komatsubara, C. Schank, C. Geibel and F. Steglich, Physica B 186-188 (1993) 612.
Physica B 186-188 (1993) 661-663 North-Holland
Physical properties of antiferromagnetic ternary compound SmPd2A13 H. Kitazawa a, A. Mori b, S. Takano b, T. Yamadaya b, A. Matsushita c, and T. M a t s u m o t o c "The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan bYokohama City University, Kanazawa-ku, Yokohama 236, Japan ~National Research Institute for Metals, Tokyo 153, Japan Measurements of electrical resistivity, magnetic susceptibility and specific heat have been performed on a new ternary compound SmPd2AI3. The results indicate that the valence of Sm ions is almost trivalent and that SmPd2AI3 has a complicated magnetic phase diagram below 12 K.
Recently, the project of development of new ternary rare earth and actinide compounds, which show exotic physical properties, led to the discovery of new ternary compounds RPd2A13 (R: rare earth and actinide elements) with the hexagonal PrNi~A13 type structure. Among them, it was found that UPd2AI 3 and CePd2A13 were interesting substances. The former is a new heavy-fermion superconductor ( T c = 2 K , TN = 14 K) [1] and the latter is a new heavy fermion substance which exhibits an antiferromagnetic ordering below T N = 2.8 K [2]. In this article, we present the first results of the magnetic, transport and thermal properties of SmPd2AI 3 with a homologous structure by measurement of magnetic susceptibility, electrical resistivity and specific heat. Polycrystalline samples of SmPd2A13 were synthesized by arc-melting the stoichiometric mixtures of 3N-Sm, 3N-Pd and 5N-AI in an argon atmosphere. As-cast samples were annealed at 900°C for 120 h in a high vacuum. The pattern of X-ray powder diffraction agrees well with a calculated diffraction pattern for the hexagonal PrNi2Al3-type structure. The lattice constants were determined to be a = 5.41310(5)A and c = 4.19971(6) A by the whole-powder-pattern-decomposition (WPPD) method [3]. The volume of already observed homologous compounds RPd2A13 (R = La, Ce [2] and Sm) monotonously decreases with the radius of R 3+ ion. It suggests that the valence of Sm
ions is almost trivalent. The electrical resistivity was measured by the conventional four-terminal DC method in the temperature range 1.7-300 K. The specific heat between 1.5 and 4 0 K was measured using the conventional adiabatic technique. The susceptibility, X, and magnetization, M, in the field range 0 . 1 - 4 T and in the temperature range 1.7-300K were measured by a SQUID magnetometer (CCL Co.). The powdered and parallelpiped samples were used for the measurements of X and M, respectively. The overall temperature dependence of the electrical resistivity in SmPd2A13 exhibits metallic behavior as in the case of nonmagnetic LaPd2AI 3 as shown in fig. 1. However, a cusp is clearly observed at 12 K in SmPd2A13. This cusp suggests the presence of mag-
Correspondence to: H. Kitazawa, The Institute of Physical and Chemical Research (RIKEN) Wako, Saitama 351-01, Japan.
Fig. 1. The electrical resistivity R(T) of SmPd2A13 and LaPd2Al3 as a function of temperature. The inset shows p(T) of SmPd2A13 on an enlarged scale around the anomaly.
200
I
40
T1
~35
L,,,,~,~,~ ~°o"~
oE 150
SmPd 2AI3
> 100 ._~
rr 50
0
. . . .
0
0921-4526/93/$06.00 © 1993- Elsevier Science Publishers B.V. All rights reserved
i
. . . .
50
i
.
.
.
.
i
. . . .
i
. . . .
100 150 200 Temperature ( K )
i
. . . .
250
300
662
H. Kitazawa et al. / Physical properties of SmPd:AI,
netic ordering below T 1 = 12 K and is discussed later. Figure 2 shows the temperature dependence of the specific heat, C(T), of SmPd2A13 and LaPd2A13. Two large peaks of the A-type were clearly observed at 12 K (T1) and 4.3K ( T 2 ) . Moreover, a small shoulder, which is located in the vicinity of the large peak at 4.3 K, is visible at 4.0 K (T3) as shown in the inset. Therefore, there are three phase transition temperatures, T t, T~ and T3, above 1.5 K under zero field. The magnetic part of specific heat, C m, for SmPd2A13 was derived by subtracting the specific heat of the nonmagnetic LaPd2AI 3 as a phonon contribution. When the magnetic contribution to the entropy is neglected below 1.65 K, the value of the magnetic entropy reaches to 0 . 8 9 R l n 2 at 20K. A J = 5 / 2 multiplet of Sm 3+, which is sixfold degenerate, splits into three doublets by the hexagonal crystalline electrical field (CEF). The value of the obtained entropy indicates that the ground state is doublet. The Schottky anomaly is not observed up to 40 K in comparison with CePd2AI3, which has a maximum at 14 K [4]. At least, it is suggested that the first excited state is apart from the ground state by the order of 100K in SmPd2AI ~. Thus, this system is clearly influenced by the CEF effect. The susceptibility of LaPd2A13, which is paramagnetic, is found to be 6.0 × 10 5 emu/mol at room temperature and almost temperature independent. The electrical specific heat coefficient, 7, of LaPd:AI 3 was found to be 8 . 8 m J / m o l K 2 from the C / T versus T 2 plot. The 4f-spin susceptibility, XSm--XL~, in SmPd2AI 3 was estimated from the difference between Xsm and XL,, where XSm and XL, are the susceptibilities of SmPd2AI 3 and LaPdzAI 3, respectively. The temperature dependence of Xsm- XL~ between 1.7 and 300 K under the magnetic field of 0.1 T is shown in Fig. 3(a). It is clearly found that three peaks observed 35
8
30
.=Sm
25
~e" i,
o
E
20
/
°
R = La 2
15
O
T2
lO
T1 v
~
0
5
10
o°
o 3
4
\oo.°-"
1 5
I6
o°. oo:.
oo-
o~:." oO.~."
15 20 25 30 Temperature ( K )
"
R = La
35
40
Fig. 2. Temperature dependence of the specific heat of SmPd2AI3 and LaPd2AI3 between 1.5 and 40 K.
0.06
1200 SmPd 2 AI 3 i H=O.IT , . . . . ~ ~ " ' ~
0.05
1000
0.04
800
0.03
600 2z
;~ 0.02
400 /
Sm3*
(a)
0.01
0.00
200
50
250
20O r308
Temperature ( K )
0.06 5 E
2
•go%131"2 T
0.05
110oo
(b) ] t800 E
SmPd2 a13
0.04
H:O.1T
T,
0.03
tooo
E 0.02
o*
0.01 0.00
0 ,4 , .
8 e
-
.e~el ; o ~ . . T(K)
"
16o~28
]200 --
Fig. 3. (a) Temperature dependence of 4f-spin susceptibility, XSm--Xt.~, (O) and its inverse, 1/()(Sm-XL,) (O) in SmPd2AI3 under H = 0.1 T. (b) XSm--XL, and 1/(Xs,, X,~) as a function of temperature are shown on an enlarged scale at low temperatures. in C(T) are attributed to the magnetic phase transition and correspond to the anomalies of X as shown in fig. 3(b). With decreasing temperature, X changes as follows: (1) steep increase from 12K (T,); (2) two maxima at 10 and 4.3 K (T2) and (3) steep increase again from 4.0K (T3). The solid curve exhibits the contribution of free Sm 3÷ ions whose 4f state has an energy separation of 1500K between the ground J = 5/2 and the first excited J = 7/2 muitiplets. The temperature dependence of 1/(Xs m --XL,) indicates that the valence of Sm is almost trivalent rather than divalent. The deviation from the solid curve may be explained by the CEF effect and the exchange interaction. Figure 4 shows the magnetization, M ( T ) , as a function of temperature under the various magnetic fields. Although T~ and T 2 a r e not so influenced by field up to 4 T, T 3 shifts to the lower temperature with increasing field. The maximum observed at 10 K under 0.1 T smears out with increasing field. On the other hand, the other faint maximum observed around T2 under
H. Kitazawa et al. / Physical properties of SmPd,AI 3 0.030 "~"
0.025
4 T -..
,'"
~'~ ~ ~.=
0,020
3 T
•"
0.015
2T
,~
~
• • mm =" =
v
.-~
served in T < T 3 is too small, it is not obvious whether this is attributed to the intrinsic ferromagnetic component or the impurity. In summary, the measurements of lattice constants and X reveal that the valence of Sm is almost trivalent in SmPd2Al 3. This compound clearly has a complicated magnetic phase diagram and is influenced by the CEF effect. Further measurements to clarify the magnetic properties of SmPd2A13 are in progress.
S m P d 2AI 3
•,,,.
== •
•
=
===
=
=
==
0.01 0 0.5 T " ~ 0.005 0.1 T
° °~o o o o •.
~'°"
C~=OOq~q~
. . . . . . .
0.000 0
"'e
"
O,OO. CIOOOOOO O ~
5
D
o
°
" ° ° l
o DD
O O?.O
10
663
° Oo D n D " e I = . p~,,~.O
15
The authors are grateful to Mr. Y. Iimura for X-ray analysis.
Temperature ( K )
Fig. 4. Magnetization of SmPd2A13 as a function of temperature under the various magnetic fields.
References
0.1 T develops into a prominent broad peak with increasing field. When field above 2 T is applied, the amplitude of magnetization at T2 is greater than that below T 3. The field dependence of M at 1.7 K reveals a small remanence of about 0.003k%/Sm. However, a hysteresis phenomena and remanence were not observed in the M ( H ) curve with constant temperature of 4.2 K. At least, it is thought that the magnetic moments antiferromagnetically order in the narrow region between T 2 and T 3. Since the remanence ob-
[1] C. Geibel, C. Schank, S. Thies, H. Kitazawa, C.D. Bred|, A. B6hm, M. Rau, A. Grauel, R. Caspary, R. Helfrich, U. Ahlheim, G. Weber and F. Steglich, Z. Phys. B 84 (1991) 1. [2] H. Kitazawa, C. Schank, S. Thies, B. Seidel, C. Geibel and F. Steglich, J. Phys. Soc. Jpn. 61 (1992) 1461. [3] H. Toraya, J. Appl. Cryst. 19 (1986) 440. [4] H. Kitazawa, A. Mori, S. Takano, T. Yamadaya, A. Matsushita, T. Matsumoto, N. Sato, T. Komatsubara, C. Schank, C. Geibel and F. Steglich, Physica B 186-188 (1993) 612.