- Email: [email protected]
Single crystal growth and electrical and magnetic measurements on CeFe4Sb12
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) 277–279 www.elsevier.com/locate/jmmm
Single crystal growth and electrical and magnetic measurements on CeFe4Sb12 I. Moria, H. Sugawaraa,, K. Magishia, T. Saitoa, K. Koyamaa, D. Kikuchib, K. Tanakab, H. Satob a
Faculty of the Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502, Japan b Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan Available online 27 October 2006
Abstract We have succeeded in growing single crystals of CeFe4 Sb12 by a Sb-self-flux method and measured the electrical resistivity and magnetization. The residual resistivity is about two times smaller than that of polycrystalline ones, suggesting that the sample quality is highly improved. The magnetization measurements at low temperature revealed that the sample contains almost no magnetic impurities which are always observed in polycrystalline samples. The weak temperature dependence and a broad maximum around 115 K in magnetic susceptibility, which is a typical feature of valence fluctuation compounds, have been observed. r 2006 Elsevier B.V. All rights reserved. PACS: 75.30.Mb; 72.27.+a Keywords: Filled skutterudite; CeFe4 Sb12 ; Single crystal
Ternary intermetallic compounds RT 4 X 12 (R ¼ rare earth; T ¼ Fe, Ru and Os; X ¼ P, As and Sb) crystallized in the filled skutterudite structure ðIm3Þ have attracted considerable attention because of their various novel phenomena, i.e., unconventional superconductivity, metal–insulator transition, heavy fermion behavior, etc., and also their prospect for thermoelectric applications [1,2]. Among them, most of Cebased CeT 4 X 12 compounds show a semiconducting behavior that is probably caused by the formation of an energy gap DE g due to the hybridization between the 4f- and conduction electrons. In fact, DE g estimated from the temperature dependence of electrical resistivity can be roughly scaled by the lattice constant; the smaller lattice constant ones, such as for CeFe4 P12 and CeRu4 P12 , have the larger energy gap [3]. The Ce-based filled skutterudite antimonides CeT 4 Sb12 , which have the largest lattice constant in CeT 4 X 12 , are metallic and show interesting anomalous behaviors such as non-fermi-liquid behavior in CeRu4 Sb12 [4] and Kondoinsulating behavior in CeOs4 Sb12 [5]. For CeFe4 Sb12 , the Corresponding author. Tel.: +81 88 656 7229; fax: +81 88 656 7665.
E-mail address: [email protected] (H. Sugawara). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.044
polycrystalline samples have been synthesized and investigated various physical properties, in which the heavy fermion behavior and large thermoelectric efficiency were reported in the early papers [6,7]. Recently, Viennois et al. have investigated the electrical resistivity rðTÞ, magnetic susceptibility wðTÞ and specific heat CðTÞ [8]. They reported that this compound shows a broad maximum around 130 K in the 4fcomponents of rðTÞ, wðTÞ and CðTÞ. They consistently explained the maxima both in rðTÞ and CðTÞ, assuming the combined effect of Kondo effect with the Kondo temperature T K 60280 K and the crystalline electric field (CEF) effect of splitting temperature DCEF 330 K above the doublet ground state. However, no explanation was proposed on the maximum in wðTÞ that have been usually discussed in correlation with the valence fluctuation phenomena. For the better understanding of these unusual behaviors, the preparation of high-quality single crystal sample is essential. In this paper we report on the first experimental results of electrical resistivity and magnetization on single crystal samples. Single crystals of CeFe4 Sb12 were grown by usual Sb-selfflux method; the starting composition is Ce:Fe:Sb ¼ 1:4:20. Single crystals of reference compound LaFe4 Sb12 were grown
ARTICLE IN PRESS I. Mori et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 277–279
278
0.01
ing clear log T dependence and shows a maximum at T rmax ¼ 94 K, which is similar to those of ordinary heavy fermion compounds. After showing a shallow minimum at T rmin 40 K, again Dr increases logarithmically with decreasing temperature down to 10 K and shows saturating tendency at lower temperatures. Such a temperature dependence of Dr is qualitatively the same with previous report except the absolute values of characteristic temperatures T rmax and T rmin as to be 130 and 50 K, respectively, in Ref. [8]. The higher-temperature log T dependence is ascribed to the Kondo scattering using all the channels and the maximum gives the corresponding Kondo temperature (T hK ) while the lower-temperature one reflects the Kondo effect due to CEF ground state doublet. By putting T hK 100 K and DCEF 330 K into the relation T hK ¼ ðD2CEF T K Þ1=3 [3], T K is estimated to be 10 K. Fig. 1(b) shows the temperature dependence of magnetic susceptibility wðTÞ both in CeFe4 Sb12 and LaFe4 Sb12 . For LaFe4 Sb12 , the behavior of wðTÞ is close to the previous work except the small difference of absolute value; wðTÞ shows the Curie–Weiss (CW)-like behavior above 200 K with effective magnetic moment meff ¼ 2:0 mB and paramagnetic CW temperature yP ¼ 34 K. Such CW-like behavior in LaFe4 Sb12 was explained by the itinerant magnetism of the Fe 3d-band possessing the spin fluctuations [9]. On the other hand, for CeFe4 Sb12 , the behavior is highly different from those of previous reports especially at low temperatures [6–8]. In the present single crystal sample, no drastic upturn has been observed at low temperatures, which was always observed in polycrystalline samples. As pointed out in the previous reports, the upturn of wðTÞ is due to the magnetic impurity, most probably CeSb2 (T C ¼ 15 KÞ. No such a ferromagnetic impurity effect can be also seen in the magnetization curve at 2 K in the present sample as shown in the inset of Fig 1(b). Therefore, combining with the smaller residual resistivity, the sample quality is highly improved in the present single crystal. The wðTÞ of CeFe4 Sb12 is larger than that of LaFe4 Sb12 at room temperature, and clearly shows a broad maximum around 115 K without subtracting wðTÞ of LaFe4 Sb12 . The broad maximum in wðTÞ is a typical features of valence fluctuation compounds, however, that is inconsistent with the results of resistivity measurement as already reported in polycrystalline samples. Such unusual behaviors are also observed in the CeRu4 Sb12 [4], which is a unique property of Ce-based filled skutterudite antimonides.
0
This work was supported by a Grant-in-Aid for Scientific Research Priority Area Skutterudite (No. 15072206) of the Ministry of Education, Culture, Sports, Science and Technology, Japan, and Iketani grant project.
by the same manner. The raw materials were 3N (99.9% pure)- Ce, 3N-La, 4N-Fe and 6N-Sb. We have mechanically isolated the single crystals from flux, since the crystal itself is dissolved by the aqua regia almost as easily as Sb-flux. The samples were characterized both by the powder X-ray diffraction and back Laue methods. The electrical resistivity was measured by the ordinary four-probe DC method using a 3 He cryostat down to 0:4 K and the magnetic measurements were made by a Quantum Design SQUID magnetometer up to 7 T. Fig. 1(a) shows the temperature dependence of electrical resistivity rðTÞ both in CeFe4 Sb12 and LaFe4 Sb12 . The general features in rðTÞ are almost the same with previous reports on polycrystalline samples, despite the improvement of residual resistivity of about two times [7,8]. For CeFe4 Sb12 , rðTÞ shows a weak temperature dependence above 100 K below which it decreases rapidly with decreasing temperature. On the other hand, for LaFe4 Sb12 , rðTÞ decreases monotonously with decreasing temperature suggesting that the phonon contribution is dominant. Here, we note that no superconductivity has been observed down to 0:4 K in LaFe4 Sb12 though the most La-based skutterudites show superconductivity, which may be related to the magnetic fluctuations due to the large electronic density of states of Fe 3d-band at Fermi energy [9,10]. As shown in the inset of Fig. 1(a), the 4f-component of resistivity Dr ¼ rðCeFe4 Sb12 Þ rðLaFe4 Sb12 Þ increases with decreasing temperature follow-
(a)
ρ (μΩ cm)
300
200
100
0 0.02
χ (emu/mol)
(b)
0
100
200
300
T (K) Fig. 1. Temperature dependence of (a) the electrical resistivity and (b) magnetic susceptibility both in CeFe4 Sb12 and LaFe4 Sb12 . The inset of (a) shows the 4f-component of resistivity in CeFe4 Sb12 . The inset of (b) shows the magnetization curves at 2 K.
References [1] Y. Aoki, H. Sugawara, H. Harima, H. Sato, J. Phys. Soc. Japan 74 (2005) 209.
ARTICLE IN PRESS I. Mori et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 277–279 [2] B.C. Sales, in: K.A. Gschneidner Jr., J.-C.G. Bunzli, V.K. Pecharsky (Eds.), Handbook on the Physics and Chemistry of Rare Earths, Elsevier Science B. V., Amsterdam, vol. 33, 2003, pp. 1–34 [3] H. Sugawara, S. Osaki, M. Kobayashi, T. Namiki, S.R. Saha, Y. Aoki, H. Sato, Phys. Rev. B 71 (2005) 125127. [4] N. Takeda, M. Ishikawa, J. Phys. Soc. Japan 69 (2000) 868. [5] E.D. Bauer, A. S´lebarski, E.J. Freeman, C. Sirvent, M.B. Maple, J. Phys. Condens. Matter 13 (2001) 4495. [6] D.T. Morelli, G.P. Meisner, J. Appl. Phys. 77 (1995) 3777.
279
[7] D.A. Gajewski, N. Dilley, E.D. Bauer, E.J. Freeman, R. Chau, M.B. Maple, D. Mandrus, B.C. Sales, A.H. Lacerda, J. Phys. Condens. Matter 10 (1998) 6973. [8] R. Viennois, D. Ravot, F. Terki, C. Hernandez, S. Charar, P. Haen, S. Paschen, F. Steglich, J. Magn. Magn. Mater. 272–276 (2004) e113. [9] K. Magishi, Y. Nakai, K. Ishida, H. Sugawara, I. Mori, T. Saito, K. Koyama, J. Phys. Soc. Japan 75 (2006) 023701. [10] Takegahara, Harima, J. Phys. Soc. Japan 72 (Suppl.) (2002) 240.
Journal of Magnetism and Magnetic Materials 310 (2007) 277–279 www.elsevier.com/locate/jmmm
Single crystal growth and electrical and magnetic measurements on CeFe4Sb12 I. Moria, H. Sugawaraa,, K. Magishia, T. Saitoa, K. Koyamaa, D. Kikuchib, K. Tanakab, H. Satob a
Faculty of the Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502, Japan b Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan Available online 27 October 2006
Abstract We have succeeded in growing single crystals of CeFe4 Sb12 by a Sb-self-flux method and measured the electrical resistivity and magnetization. The residual resistivity is about two times smaller than that of polycrystalline ones, suggesting that the sample quality is highly improved. The magnetization measurements at low temperature revealed that the sample contains almost no magnetic impurities which are always observed in polycrystalline samples. The weak temperature dependence and a broad maximum around 115 K in magnetic susceptibility, which is a typical feature of valence fluctuation compounds, have been observed. r 2006 Elsevier B.V. All rights reserved. PACS: 75.30.Mb; 72.27.+a Keywords: Filled skutterudite; CeFe4 Sb12 ; Single crystal
Ternary intermetallic compounds RT 4 X 12 (R ¼ rare earth; T ¼ Fe, Ru and Os; X ¼ P, As and Sb) crystallized in the filled skutterudite structure ðIm3Þ have attracted considerable attention because of their various novel phenomena, i.e., unconventional superconductivity, metal–insulator transition, heavy fermion behavior, etc., and also their prospect for thermoelectric applications [1,2]. Among them, most of Cebased CeT 4 X 12 compounds show a semiconducting behavior that is probably caused by the formation of an energy gap DE g due to the hybridization between the 4f- and conduction electrons. In fact, DE g estimated from the temperature dependence of electrical resistivity can be roughly scaled by the lattice constant; the smaller lattice constant ones, such as for CeFe4 P12 and CeRu4 P12 , have the larger energy gap [3]. The Ce-based filled skutterudite antimonides CeT 4 Sb12 , which have the largest lattice constant in CeT 4 X 12 , are metallic and show interesting anomalous behaviors such as non-fermi-liquid behavior in CeRu4 Sb12 [4] and Kondoinsulating behavior in CeOs4 Sb12 [5]. For CeFe4 Sb12 , the Corresponding author. Tel.: +81 88 656 7229; fax: +81 88 656 7665.
E-mail address: [email protected] (H. Sugawara). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.044
polycrystalline samples have been synthesized and investigated various physical properties, in which the heavy fermion behavior and large thermoelectric efficiency were reported in the early papers [6,7]. Recently, Viennois et al. have investigated the electrical resistivity rðTÞ, magnetic susceptibility wðTÞ and specific heat CðTÞ [8]. They reported that this compound shows a broad maximum around 130 K in the 4fcomponents of rðTÞ, wðTÞ and CðTÞ. They consistently explained the maxima both in rðTÞ and CðTÞ, assuming the combined effect of Kondo effect with the Kondo temperature T K 60280 K and the crystalline electric field (CEF) effect of splitting temperature DCEF 330 K above the doublet ground state. However, no explanation was proposed on the maximum in wðTÞ that have been usually discussed in correlation with the valence fluctuation phenomena. For the better understanding of these unusual behaviors, the preparation of high-quality single crystal sample is essential. In this paper we report on the first experimental results of electrical resistivity and magnetization on single crystal samples. Single crystals of CeFe4 Sb12 were grown by usual Sb-selfflux method; the starting composition is Ce:Fe:Sb ¼ 1:4:20. Single crystals of reference compound LaFe4 Sb12 were grown
ARTICLE IN PRESS I. Mori et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 277–279
278
0.01
ing clear log T dependence and shows a maximum at T rmax ¼ 94 K, which is similar to those of ordinary heavy fermion compounds. After showing a shallow minimum at T rmin 40 K, again Dr increases logarithmically with decreasing temperature down to 10 K and shows saturating tendency at lower temperatures. Such a temperature dependence of Dr is qualitatively the same with previous report except the absolute values of characteristic temperatures T rmax and T rmin as to be 130 and 50 K, respectively, in Ref. [8]. The higher-temperature log T dependence is ascribed to the Kondo scattering using all the channels and the maximum gives the corresponding Kondo temperature (T hK ) while the lower-temperature one reflects the Kondo effect due to CEF ground state doublet. By putting T hK 100 K and DCEF 330 K into the relation T hK ¼ ðD2CEF T K Þ1=3 [3], T K is estimated to be 10 K. Fig. 1(b) shows the temperature dependence of magnetic susceptibility wðTÞ both in CeFe4 Sb12 and LaFe4 Sb12 . For LaFe4 Sb12 , the behavior of wðTÞ is close to the previous work except the small difference of absolute value; wðTÞ shows the Curie–Weiss (CW)-like behavior above 200 K with effective magnetic moment meff ¼ 2:0 mB and paramagnetic CW temperature yP ¼ 34 K. Such CW-like behavior in LaFe4 Sb12 was explained by the itinerant magnetism of the Fe 3d-band possessing the spin fluctuations [9]. On the other hand, for CeFe4 Sb12 , the behavior is highly different from those of previous reports especially at low temperatures [6–8]. In the present single crystal sample, no drastic upturn has been observed at low temperatures, which was always observed in polycrystalline samples. As pointed out in the previous reports, the upturn of wðTÞ is due to the magnetic impurity, most probably CeSb2 (T C ¼ 15 KÞ. No such a ferromagnetic impurity effect can be also seen in the magnetization curve at 2 K in the present sample as shown in the inset of Fig 1(b). Therefore, combining with the smaller residual resistivity, the sample quality is highly improved in the present single crystal. The wðTÞ of CeFe4 Sb12 is larger than that of LaFe4 Sb12 at room temperature, and clearly shows a broad maximum around 115 K without subtracting wðTÞ of LaFe4 Sb12 . The broad maximum in wðTÞ is a typical features of valence fluctuation compounds, however, that is inconsistent with the results of resistivity measurement as already reported in polycrystalline samples. Such unusual behaviors are also observed in the CeRu4 Sb12 [4], which is a unique property of Ce-based filled skutterudite antimonides.
0
This work was supported by a Grant-in-Aid for Scientific Research Priority Area Skutterudite (No. 15072206) of the Ministry of Education, Culture, Sports, Science and Technology, Japan, and Iketani grant project.
by the same manner. The raw materials were 3N (99.9% pure)- Ce, 3N-La, 4N-Fe and 6N-Sb. We have mechanically isolated the single crystals from flux, since the crystal itself is dissolved by the aqua regia almost as easily as Sb-flux. The samples were characterized both by the powder X-ray diffraction and back Laue methods. The electrical resistivity was measured by the ordinary four-probe DC method using a 3 He cryostat down to 0:4 K and the magnetic measurements were made by a Quantum Design SQUID magnetometer up to 7 T. Fig. 1(a) shows the temperature dependence of electrical resistivity rðTÞ both in CeFe4 Sb12 and LaFe4 Sb12 . The general features in rðTÞ are almost the same with previous reports on polycrystalline samples, despite the improvement of residual resistivity of about two times [7,8]. For CeFe4 Sb12 , rðTÞ shows a weak temperature dependence above 100 K below which it decreases rapidly with decreasing temperature. On the other hand, for LaFe4 Sb12 , rðTÞ decreases monotonously with decreasing temperature suggesting that the phonon contribution is dominant. Here, we note that no superconductivity has been observed down to 0:4 K in LaFe4 Sb12 though the most La-based skutterudites show superconductivity, which may be related to the magnetic fluctuations due to the large electronic density of states of Fe 3d-band at Fermi energy [9,10]. As shown in the inset of Fig. 1(a), the 4f-component of resistivity Dr ¼ rðCeFe4 Sb12 Þ rðLaFe4 Sb12 Þ increases with decreasing temperature follow-
(a)
ρ (μΩ cm)
300
200
100
0 0.02
χ (emu/mol)
(b)
0
100
200
300
T (K) Fig. 1. Temperature dependence of (a) the electrical resistivity and (b) magnetic susceptibility both in CeFe4 Sb12 and LaFe4 Sb12 . The inset of (a) shows the 4f-component of resistivity in CeFe4 Sb12 . The inset of (b) shows the magnetization curves at 2 K.
References [1] Y. Aoki, H. Sugawara, H. Harima, H. Sato, J. Phys. Soc. Japan 74 (2005) 209.
ARTICLE IN PRESS I. Mori et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 277–279 [2] B.C. Sales, in: K.A. Gschneidner Jr., J.-C.G. Bunzli, V.K. Pecharsky (Eds.), Handbook on the Physics and Chemistry of Rare Earths, Elsevier Science B. V., Amsterdam, vol. 33, 2003, pp. 1–34 [3] H. Sugawara, S. Osaki, M. Kobayashi, T. Namiki, S.R. Saha, Y. Aoki, H. Sato, Phys. Rev. B 71 (2005) 125127. [4] N. Takeda, M. Ishikawa, J. Phys. Soc. Japan 69 (2000) 868. [5] E.D. Bauer, A. S´lebarski, E.J. Freeman, C. Sirvent, M.B. Maple, J. Phys. Condens. Matter 13 (2001) 4495. [6] D.T. Morelli, G.P. Meisner, J. Appl. Phys. 77 (1995) 3777.
279
[7] D.A. Gajewski, N. Dilley, E.D. Bauer, E.J. Freeman, R. Chau, M.B. Maple, D. Mandrus, B.C. Sales, A.H. Lacerda, J. Phys. Condens. Matter 10 (1998) 6973. [8] R. Viennois, D. Ravot, F. Terki, C. Hernandez, S. Charar, P. Haen, S. Paschen, F. Steglich, J. Magn. Magn. Mater. 272–276 (2004) e113. [9] K. Magishi, Y. Nakai, K. Ishida, H. Sugawara, I. Mori, T. Saito, K. Koyama, J. Phys. Soc. Japan 75 (2006) 023701. [10] Takegahara, Harima, J. Phys. Soc. Japan 72 (Suppl.) (2002) 240.