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Physical properties of SmMIn5 (M=Co , Rh, Ir)
ARTICLE IN PRESS
Physica B 378–380 (2006) 421–422 www.elsevier.com/locate/physb
Physical properties of SmMIn5 (M ¼ Co, Rh, Ir) Y. Inadaa,, M. Hedob, T. Fujiwarab, T. Sadamasab, Y. Uwatokoa a
Phys. II Laboratory, Department of Science Education, Faculty of Education, Okayama University, 700 8530, Japan b ISSP, University of Tokyo, Kashiwa 277 8581, Japan
Abstract SmMIn5 ðM ¼ Co; Rh; IrÞ crystallizes in the tetragonal HoCoGa5-type structure. This type of crystal structure is noticed as tetragonal variants of the AuCu3 -structure, in which new superconductors were discovered. PuCoGa5 and PuRhGa5 are also the interesting superconductors. On the other hand, it is expected that Sm has a ground state similar to Pu compounds. We have succeeded in growing single crystals of SmMIn5 by the flux method. SmRhIn5 and SmIrIn5 showed the antiferromagnetic ordering and extra transitions below T N , which is almost same as the results in the previous report. We have succeeded in growing single crystals of SmCoIn5. It also showed the antiferromagnetic ordering and extra transitions below T N ¼ 11:9 K. The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn5 compounds. r 2006 Elsevier B.V. All rights reserved. PACS: 74.25.Ha; 75 Keywords: SmCoIn5; Superconductivity; Magnetism
The tetragonal HoCoGa5-type crystal structure is known as a tetragonal variant of the AuCu3-strucuture in which new superconductors were discovered [1,2]. CeMIn5 ðM ¼ Co; Rh; IrÞ compounds exhibit a variety of interesting properties such as non-s-superconductivity, a first-order transition near the upper critical field, heavy-fermion behavior, pressure-induced superconductivity, etc. [3,4]. PuCoGa5 and PuRhGa5 are known as heavy-fermion ‘‘high T c ’’ superconductors [2,5]. In the exotic heavyfermion superconductors, Cooper pairs are expected formed by the exchange of magnetic spin fluctuations, in which f-electrons which are not simply localized play an important role. A large specific heat coefficient and Curie–Weiss behavior in the normal state or low antiferromagnetic ordering temperatures are features of the exotic heavy-fermion superconductors. Pu has valence states of Pu3þ ð5f 5 Þ, Pu4þ ð5f 4 Þ Pu5þ , Pu6þ in Pu-based compounds, while Sm has Sm2þ ð4f 6 Þ, Sm3þ ð4f 5 Þ. Sm3þ ð4f 5 Þ and Pu3þ ð5f 5 Þ ions have the same J ¼ 52 multiplet, and show the local moment behavior, i.e., obey a Curie–Weiss law. It is interesting that it depends on Corresponding author.
E-mail address: [email protected] (Y. Inada). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.01.148
the particular crystal structure whether Sm compounds show exotic behavior or not. We have succeeded in growing single crystals of SmMIn5 ðM ¼ Co; Rh; IrÞ by the flux method. The physical properties of single crystals of SmRhIn5 and SmIrIn5 have already been reported [6], but there is no report on singlecrystalline SmCoIn5. Specific heat measurements were carried out using the thermal-relaxation method. Magnetization measurements were made in a Quantum Design DC superconducting quantum interference device. Electrical resistivity measurements were performed by the conventional AC four-probe method. Fig. 1 shows the specific heat divided by temperature and the corresponding magnetic entropy below 30 K, for SmRhIn5, LaRhIn5 (a) and SmIrIn5, LaIrIn5 (b). The non-magnetic contribution of LaRhIn5 or LaIrIn5 has been subtracted from the specific heat of SmRhIn5 or SmIrIn5 to calculate the magnetic entropy. Two clear peaks were observed, of which the upper one corresponds to the antiferromagnetic order. The upper transition temperature T N is 15.0 and 14.9 K for SmRhIn5 and SmIrIn5, respectively. The lower transition temperature is 8.3 and 11.0 K for SmRhIn5 and SmIrIn5, respectively. In Ref. [6], a small, not sharp, maximum in C=T has been reported in
ARTICLE IN PRESS Y. Inada et al. / Physica B 378–380 (2006) 421–422
422
2 C/T (J/mol K2)
C/T (J/mol K2)
2 SmRhIn5 1
1 SmCoIn5
LaRhIn5 0 Rln4
5
Rln2
3
SmRhIn5 0
0
0
10
20
30
χ (10-3emu/mol)
S mag (J/mol K)
(a)
10
H⊥c
2 H // c SmCoIn5
Temperature (K)
(a)
0
C/T (J/mol K2)
2
1 LaIrIn5
S mag (J/mol K)
0 Rln4
5
Rln2 SmIrIn5
0 (b)
0
10
20
20
30
Fig. 2. (a) Specific heat divided by temperature versus temperature for SmCoIn5, and (b) static magnetic susceptibility w of SmCoIn5, measured in an applied field of 1 kOe.
SmIrIn5
10
10 Temperature (K)
(b)
30
Temperature (K)
Fig. 1. Specific heat divided by temperature and corresponding magnetic entropy as a function of temperature for (a) SmRhIn5 and (b) SmIrIn5.
both compounds at almost the same temperature as in our present results. At T N , in both compounds, the magnetic entropy is about 75% of R ln 4 at T N . At the lower transition temperature, the magnetic entropy is about 40% of R ln 2 in SmRhIn5, and about 70% of R ln 2 in SmIrIn5. In the case of SmSn3 with AuCu3 cubic crystal structure, the magnetic entropy is about 80% of R ln 4 at the quadrupolar ordering temperature T Q and almost R ln 2 at T N [7]. Below T Q , SmSn3 shows two sharp peaks associated with magnetic transitions. The ground-state level of SmSn3 is a G8 quartet [7], but in the tetragonal crystal structure, G8 quartet splits into two doublets, leading to three doublets. It is probable that there are two adjacent doublet levels in SmRhIn5 and SmIrIn5, as mentioned in Ref. [6]. It seems that the lower sharp transition does not substantially contribute to release the magnetic entropy especially in SmRhIn5. Although it is not clear, there is a possibility that the lower sharp transition is
associated with a spin reorientation. A direct observation is necessary to reveal the magnetic structure. Fig. 2(a) shows the specific heat divided by temperature versus temperature for SmCoIn5, and Fig. 2(b) the static magnetic susceptibility measured in an applied field of 0.1 T for the field along the c-axis (triangles) and perpendicular to the c-axis (circles) below 30 K. The magnetic susceptibility shows anisotropic behavior similar to SmRhIn5 and SmIrIn5, which is expected for antiferromagnetic ordering. Three peaks are observed in the temperature dependence of C=T, and the highest one has the largest jump. Also in the magnetic susceptibility three anomalies are observed, corresponding to the three peaks in C=T. The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn5 compounds. It is expected that SmCoIn5 is more near to the delocalized state than SmRhIn5 and SmIrIn5. However, the value of C=T at 2 K in SmCoIn5 is 53 mJ/ mol K2 which is not a large value compared to PuCoGa5 or PuRhGa5. Therefore, it may be concluded that the 4f electrons in SmCoIn5 are localized adn not itinerant. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant no. 16540317). References [1] [2] [3] [4] [5] [6] [7]
J.D. Thompson, et al., J. Magn. Magn. Mater. 226 (2001) 5. J.L. Sarrao, et al., Nature 420 (2002) 297. A. Bianchi, et al., Phys. Rev. Lett. 91 (2003) 187004. H. Hegger, et al., Phys. Rev. Lett. 84 (2000) 4986. F. Wastin, et al., J. Phys.: Condens. Matter 15 (2003) S2279. P.G. Pagliuso, et al., Phys. Rev. B 63 (2001) 054426. M. Kasaya, et al., J. Magn. Magn. Mater. 52 (1985) 289.
Physica B 378–380 (2006) 421–422 www.elsevier.com/locate/physb
Physical properties of SmMIn5 (M ¼ Co, Rh, Ir) Y. Inadaa,, M. Hedob, T. Fujiwarab, T. Sadamasab, Y. Uwatokoa a
Phys. II Laboratory, Department of Science Education, Faculty of Education, Okayama University, 700 8530, Japan b ISSP, University of Tokyo, Kashiwa 277 8581, Japan
Abstract SmMIn5 ðM ¼ Co; Rh; IrÞ crystallizes in the tetragonal HoCoGa5-type structure. This type of crystal structure is noticed as tetragonal variants of the AuCu3 -structure, in which new superconductors were discovered. PuCoGa5 and PuRhGa5 are also the interesting superconductors. On the other hand, it is expected that Sm has a ground state similar to Pu compounds. We have succeeded in growing single crystals of SmMIn5 by the flux method. SmRhIn5 and SmIrIn5 showed the antiferromagnetic ordering and extra transitions below T N , which is almost same as the results in the previous report. We have succeeded in growing single crystals of SmCoIn5. It also showed the antiferromagnetic ordering and extra transitions below T N ¼ 11:9 K. The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn5 compounds. r 2006 Elsevier B.V. All rights reserved. PACS: 74.25.Ha; 75 Keywords: SmCoIn5; Superconductivity; Magnetism
The tetragonal HoCoGa5-type crystal structure is known as a tetragonal variant of the AuCu3-strucuture in which new superconductors were discovered [1,2]. CeMIn5 ðM ¼ Co; Rh; IrÞ compounds exhibit a variety of interesting properties such as non-s-superconductivity, a first-order transition near the upper critical field, heavy-fermion behavior, pressure-induced superconductivity, etc. [3,4]. PuCoGa5 and PuRhGa5 are known as heavy-fermion ‘‘high T c ’’ superconductors [2,5]. In the exotic heavyfermion superconductors, Cooper pairs are expected formed by the exchange of magnetic spin fluctuations, in which f-electrons which are not simply localized play an important role. A large specific heat coefficient and Curie–Weiss behavior in the normal state or low antiferromagnetic ordering temperatures are features of the exotic heavy-fermion superconductors. Pu has valence states of Pu3þ ð5f 5 Þ, Pu4þ ð5f 4 Þ Pu5þ , Pu6þ in Pu-based compounds, while Sm has Sm2þ ð4f 6 Þ, Sm3þ ð4f 5 Þ. Sm3þ ð4f 5 Þ and Pu3þ ð5f 5 Þ ions have the same J ¼ 52 multiplet, and show the local moment behavior, i.e., obey a Curie–Weiss law. It is interesting that it depends on Corresponding author.
E-mail address: [email protected] (Y. Inada). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.01.148
the particular crystal structure whether Sm compounds show exotic behavior or not. We have succeeded in growing single crystals of SmMIn5 ðM ¼ Co; Rh; IrÞ by the flux method. The physical properties of single crystals of SmRhIn5 and SmIrIn5 have already been reported [6], but there is no report on singlecrystalline SmCoIn5. Specific heat measurements were carried out using the thermal-relaxation method. Magnetization measurements were made in a Quantum Design DC superconducting quantum interference device. Electrical resistivity measurements were performed by the conventional AC four-probe method. Fig. 1 shows the specific heat divided by temperature and the corresponding magnetic entropy below 30 K, for SmRhIn5, LaRhIn5 (a) and SmIrIn5, LaIrIn5 (b). The non-magnetic contribution of LaRhIn5 or LaIrIn5 has been subtracted from the specific heat of SmRhIn5 or SmIrIn5 to calculate the magnetic entropy. Two clear peaks were observed, of which the upper one corresponds to the antiferromagnetic order. The upper transition temperature T N is 15.0 and 14.9 K for SmRhIn5 and SmIrIn5, respectively. The lower transition temperature is 8.3 and 11.0 K for SmRhIn5 and SmIrIn5, respectively. In Ref. [6], a small, not sharp, maximum in C=T has been reported in
ARTICLE IN PRESS Y. Inada et al. / Physica B 378–380 (2006) 421–422
422
2 C/T (J/mol K2)
C/T (J/mol K2)
2 SmRhIn5 1
1 SmCoIn5
LaRhIn5 0 Rln4
5
Rln2
3
SmRhIn5 0
0
0
10
20
30
χ (10-3emu/mol)
S mag (J/mol K)
(a)
10
H⊥c
2 H // c SmCoIn5
Temperature (K)
(a)
0
C/T (J/mol K2)
2
1 LaIrIn5
S mag (J/mol K)
0 Rln4
5
Rln2 SmIrIn5
0 (b)
0
10
20
20
30
Fig. 2. (a) Specific heat divided by temperature versus temperature for SmCoIn5, and (b) static magnetic susceptibility w of SmCoIn5, measured in an applied field of 1 kOe.
SmIrIn5
10
10 Temperature (K)
(b)
30
Temperature (K)
Fig. 1. Specific heat divided by temperature and corresponding magnetic entropy as a function of temperature for (a) SmRhIn5 and (b) SmIrIn5.
both compounds at almost the same temperature as in our present results. At T N , in both compounds, the magnetic entropy is about 75% of R ln 4 at T N . At the lower transition temperature, the magnetic entropy is about 40% of R ln 2 in SmRhIn5, and about 70% of R ln 2 in SmIrIn5. In the case of SmSn3 with AuCu3 cubic crystal structure, the magnetic entropy is about 80% of R ln 4 at the quadrupolar ordering temperature T Q and almost R ln 2 at T N [7]. Below T Q , SmSn3 shows two sharp peaks associated with magnetic transitions. The ground-state level of SmSn3 is a G8 quartet [7], but in the tetragonal crystal structure, G8 quartet splits into two doublets, leading to three doublets. It is probable that there are two adjacent doublet levels in SmRhIn5 and SmIrIn5, as mentioned in Ref. [6]. It seems that the lower sharp transition does not substantially contribute to release the magnetic entropy especially in SmRhIn5. Although it is not clear, there is a possibility that the lower sharp transition is
associated with a spin reorientation. A direct observation is necessary to reveal the magnetic structure. Fig. 2(a) shows the specific heat divided by temperature versus temperature for SmCoIn5, and Fig. 2(b) the static magnetic susceptibility measured in an applied field of 0.1 T for the field along the c-axis (triangles) and perpendicular to the c-axis (circles) below 30 K. The magnetic susceptibility shows anisotropic behavior similar to SmRhIn5 and SmIrIn5, which is expected for antiferromagnetic ordering. Three peaks are observed in the temperature dependence of C=T, and the highest one has the largest jump. Also in the magnetic susceptibility three anomalies are observed, corresponding to the three peaks in C=T. The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn5 compounds. It is expected that SmCoIn5 is more near to the delocalized state than SmRhIn5 and SmIrIn5. However, the value of C=T at 2 K in SmCoIn5 is 53 mJ/ mol K2 which is not a large value compared to PuCoGa5 or PuRhGa5. Therefore, it may be concluded that the 4f electrons in SmCoIn5 are localized adn not itinerant. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant no. 16540317). References [1] [2] [3] [4] [5] [6] [7]
J.D. Thompson, et al., J. Magn. Magn. Mater. 226 (2001) 5. J.L. Sarrao, et al., Nature 420 (2002) 297. A. Bianchi, et al., Phys. Rev. Lett. 91 (2003) 187004. H. Hegger, et al., Phys. Rev. Lett. 84 (2000) 4986. F. Wastin, et al., J. Phys.: Condens. Matter 15 (2003) S2279. P.G. Pagliuso, et al., Phys. Rev. B 63 (2001) 054426. M. Kasaya, et al., J. Magn. Magn. Mater. 52 (1985) 289.