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de Haas–van Alphen effect in the filled skutterudite CeRu4Sb12
Physica B 312–313 (2002) 264–266
de Haas–van Alphen effect in the filled skutterudite CeRu4Sb12 H. Sugawaraa,*, K. Abea, T.D. Matsudaa, Y. Aokia, H. Satoa, R. Settaib, b,c % Y. Onuki a
Department of Physics, Graduate School of Science, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-0397, Japan b Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan c Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Abstract We have succeeded in observing the de Haas-van Alphen effect in the filled skutterudite CeRu4 Sb12 : The results predict a large difference in the Fermi surface topology compared to the reference compound LaRu4 Sb12 : The cyclotron effective mass mnc enhanced to 4:6B5:8m0 indicates a strong electron correlation in this compound. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Filled skutterudite; CeRu4 Sb12 ; de Haas–van Alphen effect
Ternary intermetallic compounds RT4 X12 (R ¼ rare earth; T ¼ Fe; Ru, and Os; X ¼ P; As, and Sb) with the filled skutterudite structure (space group Im 3% ) have attracted much attention because of their interesting anomalous physical properties [1,2]. Among them, most of the Ce-based compounds CeT4 X12 show a semiconducting behavior that is probably caused by the formation of an energy gap Eg due to the hybridization between f- and conduction electrons. Actually, the magnitude of Eg decreases with increasing lattice constant by replacing T and X elements [3]. CeT4 Sb12 ; which has the largest lattice constants in CeT4 X12 ; is exceptionally metallic and shows interesting anomalous behaviors such as heavy-fermion behaviors in CeFe4 Sb12 [4], non-Fermi-liquid anomalies in CeRu4 Sb12 [5,6] and Kondo-insulating behavior in CeOs4 Sb12 [7]. These features must be related to the difference of delicate electronic structure in the vicinity of the Fermi level. Thus a knowledge of the electronic structure is essentially important to understand these anomalous behaviors. In this proceeding, we report the first successful de Haas–van Alphen (dHvA) experiments on CeRu4 Sb12 : *Corresponding author. Tel.: +81-426-77-2487; fax: +81426-77-2487. E-mail address: [email protected] (H. Sugawara).
Single crystals of CeRu4 Sb12 were grown by Sb-selfflux method with an excess Sb (the ratio is Ce : Ru : Sb ¼ 1 : 4 : 20). The raw materials were 4N (99.99% pure)-Ce, 4N–Ru and 6N–Sb. The process of the sample preparation is basically the same as in Ref. [5]. The residual resistivity (r0 ) and the residual resistivity ratio (RRR) of the present samples are B30 and B10 mO cm; respectively. RRu4 Sb12 (R ¼ La; Pr and Nd) grown by the same method has r0 ¼ 0:5B10 mO cm and RRR ¼ 50B100 [8,9], indicating high quality of the samples. Judging only from these r0 and RRR values, the quality of CeRu4 Sb12 samples is worse compared with those of the others. However, it is not true as discussed later. The dHvA experiments were performed in a 15 T superconducting-magnet with 3 Hecryostat down to 0:4 K: The dHvA signals were detected by means of the field modulation method. Fig. 1 shows (a) the typical dHvA oscillations and (b) its fast Fourier transformation (FFT) spectra both in LaRu4 Sb12 and CeRu4 Sb12 at 0:5 K: For LaRu4 Sb12 ; there are at least three dHvA frequency branches denoted as a; b and g: The branches a and g are observed in the limited angular ranges centered at Hjj½1 0 0; following a 1=cos y (y is a tilting field angle from the ½1 0 0). These branches may originate from the parts of the multiply connected Fermi surface (FS). The frequency branch b is observed in the whole angular range and shows only a weak angular dependence
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 2 9 8 - 4
H // [100] 0.5 K
LaRu4Sb12
CeRu4Sb12
1/H
90kOe
60kOe
(a)
α γ
LaRu4Sb12
β
CeRu4Sb12 0
1 2 dHvA Frequency (x107 Oe)
3
ln{A[1-exp(-2λm*C T/H)]/T} (arb. units)
H. Sugawara et al. / Physica B 312–313 (2002) 264–266
265
10 8
CeRu4Sb12 H // [100]
0.40K 0.46K
6
0.63K 4
0.5
1.0
dHvA Frequency (x107 Oe)
2 0
m *C= 4.8 ± 0.2m 0 0.4
0.5 T (K)
0.6
Fig. 2. Temperature dependence of the FFT spectrum (inset) and the semi-logarithmic plot of the reduced dHvA amplitude A vs. temperature. l in the vertical-axis label is a constant l ¼ 2p2 ckB =e_: mnc was estimated at around 72 kOe: Table 1 The dHvA frequencies and the cyclotron effective masses in CeRu4 Sb12 Field direction
½1 0 0
½1 1 1
½1 1 0
F ð106 OeÞ mnc ðm0 Þ
7.47 4.8
7.35 5.8
7.06 5.5
(b) Fig. 1. (a) The typical dHvA oscillations and (b) its fast Fourier transformation (FFT) spectra both in LaRu4 Sb12 and CeRu4 Sb12 :
indicating a nearly spherical FS. In contrast, for CeRu4 Sb12 ; only one dHvA frequency branch is observed as shown in Fig. 1(b). The angular dependence of frequency branch is weak suggesting that the shape of FS is also nearly spherical like b-branch in LaRu4 Sb12 : However, the absolute value of dHvA frequency F ðB7 106 OeÞ is quite small compared to b-branch (F B1:2 107 Oe), which presents the large contrast with the result of dHvA experiments in PrRu4 Sb12 [9], where the excellent agreement of dHvA branches with LaRu4 Sb12 even in the smaller frequency branch (F B2 106 Oe) is clarified suggesting a well-localized character of 4f-electrons in PrRu4 Sb12 : A large difference of the FS topology between LaRu4 Sb12 and CeRu4 Sb12 is expected, which suggests the strong c–f hybridization or the itinerant nature of 4f-electrons in CeRu4 Sb12 : From the temperature dependence of the dHvA amplitude A; we can estimate the cyclotron effective
mass mnc as shown in Fig. 2. The mnc is found to be larger by more than two times than that of the LaRu4 Sb12 despite the smaller FS; mnc ¼ 1:1B1:7m0 for LaRu4 Sb12 [9]. The dHvA frequencies and cyclotron effective masses in CeRu4 Sb12 are listed in Table 1. Compared to the Sommerfeld coefficient of B100 mJ=K2 mol [5,6], the observed mnc is too small. If we simply estimate the Sommerfeld coefficient from the FS volume and mnc in the present experiments, the value should be B10 mJ=K2 mol: This disagreement can be naturally explained if there exists another FS (s) with a heavy mass of B50m0 ; that compensates the observed one. Under the present experimental conditions, the dHvA signal for such a heavy and small FS is hardly observable, that explains why only one dHvA branch has been observed in the present experiments. Taking into account the larger lattice constant in CeRu4 Sb12 compared to the semiconducting CeT4 X12 ; the small gap might lead to the heavy mass and the semimetallic FS. The authors are grateful to Prof. H. Harima for the helpful discussion. This work was supported by the Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.
266
H. Sugawara et al. / Physica B 312–313 (2002) 264–266
References [1] H. Sato, et al., Phys. Rev. 62 (2000) 15125, and references therein. [2] H. Sugawara, et al., J. Magn. Magn. Mater. 226–230 (2001) 48. [3] I. Shirotani, et al., J. Solid State Chem. 142 (1999) 146.
[4] D.T. Morelli, G.P. Meisner, J. Appl. Phys. 77 (1995) 3777. [5] N. Takeda, M. Ishikawa, Phys. B 259–261 (1999) 92; N. Takeda, M. Ishikawa, Phys. B 281–282 (2000) 388. [6] E.D. Bauer, et al., J. Phys.: Condens. Matter 13 (2001) 5183. [7] E.D. Bauer, et al., J. Phys.: Condens. Matter 13 (2001) 4495. [8] K. Abe, et al., unpublished (in preparation for this issue). [9] T.D. Matsuda, et al., Phys. B, this issue.
de Haas–van Alphen effect in the filled skutterudite CeRu4Sb12 H. Sugawaraa,*, K. Abea, T.D. Matsudaa, Y. Aokia, H. Satoa, R. Settaib, b,c % Y. Onuki a
Department of Physics, Graduate School of Science, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-0397, Japan b Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan c Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Abstract We have succeeded in observing the de Haas-van Alphen effect in the filled skutterudite CeRu4 Sb12 : The results predict a large difference in the Fermi surface topology compared to the reference compound LaRu4 Sb12 : The cyclotron effective mass mnc enhanced to 4:6B5:8m0 indicates a strong electron correlation in this compound. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Filled skutterudite; CeRu4 Sb12 ; de Haas–van Alphen effect
Ternary intermetallic compounds RT4 X12 (R ¼ rare earth; T ¼ Fe; Ru, and Os; X ¼ P; As, and Sb) with the filled skutterudite structure (space group Im 3% ) have attracted much attention because of their interesting anomalous physical properties [1,2]. Among them, most of the Ce-based compounds CeT4 X12 show a semiconducting behavior that is probably caused by the formation of an energy gap Eg due to the hybridization between f- and conduction electrons. Actually, the magnitude of Eg decreases with increasing lattice constant by replacing T and X elements [3]. CeT4 Sb12 ; which has the largest lattice constants in CeT4 X12 ; is exceptionally metallic and shows interesting anomalous behaviors such as heavy-fermion behaviors in CeFe4 Sb12 [4], non-Fermi-liquid anomalies in CeRu4 Sb12 [5,6] and Kondo-insulating behavior in CeOs4 Sb12 [7]. These features must be related to the difference of delicate electronic structure in the vicinity of the Fermi level. Thus a knowledge of the electronic structure is essentially important to understand these anomalous behaviors. In this proceeding, we report the first successful de Haas–van Alphen (dHvA) experiments on CeRu4 Sb12 : *Corresponding author. Tel.: +81-426-77-2487; fax: +81426-77-2487. E-mail address: [email protected] (H. Sugawara).
Single crystals of CeRu4 Sb12 were grown by Sb-selfflux method with an excess Sb (the ratio is Ce : Ru : Sb ¼ 1 : 4 : 20). The raw materials were 4N (99.99% pure)-Ce, 4N–Ru and 6N–Sb. The process of the sample preparation is basically the same as in Ref. [5]. The residual resistivity (r0 ) and the residual resistivity ratio (RRR) of the present samples are B30 and B10 mO cm; respectively. RRu4 Sb12 (R ¼ La; Pr and Nd) grown by the same method has r0 ¼ 0:5B10 mO cm and RRR ¼ 50B100 [8,9], indicating high quality of the samples. Judging only from these r0 and RRR values, the quality of CeRu4 Sb12 samples is worse compared with those of the others. However, it is not true as discussed later. The dHvA experiments were performed in a 15 T superconducting-magnet with 3 Hecryostat down to 0:4 K: The dHvA signals were detected by means of the field modulation method. Fig. 1 shows (a) the typical dHvA oscillations and (b) its fast Fourier transformation (FFT) spectra both in LaRu4 Sb12 and CeRu4 Sb12 at 0:5 K: For LaRu4 Sb12 ; there are at least three dHvA frequency branches denoted as a; b and g: The branches a and g are observed in the limited angular ranges centered at Hjj½1 0 0; following a 1=cos y (y is a tilting field angle from the ½1 0 0). These branches may originate from the parts of the multiply connected Fermi surface (FS). The frequency branch b is observed in the whole angular range and shows only a weak angular dependence
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 2 9 8 - 4
H // [100] 0.5 K
LaRu4Sb12
CeRu4Sb12
1/H
90kOe
60kOe
(a)
α γ
LaRu4Sb12
β
CeRu4Sb12 0
1 2 dHvA Frequency (x107 Oe)
3
ln{A[1-exp(-2λm*C T/H)]/T} (arb. units)
H. Sugawara et al. / Physica B 312–313 (2002) 264–266
265
10 8
CeRu4Sb12 H // [100]
0.40K 0.46K
6
0.63K 4
0.5
1.0
dHvA Frequency (x107 Oe)
2 0
m *C= 4.8 ± 0.2m 0 0.4
0.5 T (K)
0.6
Fig. 2. Temperature dependence of the FFT spectrum (inset) and the semi-logarithmic plot of the reduced dHvA amplitude A vs. temperature. l in the vertical-axis label is a constant l ¼ 2p2 ckB =e_: mnc was estimated at around 72 kOe: Table 1 The dHvA frequencies and the cyclotron effective masses in CeRu4 Sb12 Field direction
½1 0 0
½1 1 1
½1 1 0
F ð106 OeÞ mnc ðm0 Þ
7.47 4.8
7.35 5.8
7.06 5.5
(b) Fig. 1. (a) The typical dHvA oscillations and (b) its fast Fourier transformation (FFT) spectra both in LaRu4 Sb12 and CeRu4 Sb12 :
indicating a nearly spherical FS. In contrast, for CeRu4 Sb12 ; only one dHvA frequency branch is observed as shown in Fig. 1(b). The angular dependence of frequency branch is weak suggesting that the shape of FS is also nearly spherical like b-branch in LaRu4 Sb12 : However, the absolute value of dHvA frequency F ðB7 106 OeÞ is quite small compared to b-branch (F B1:2 107 Oe), which presents the large contrast with the result of dHvA experiments in PrRu4 Sb12 [9], where the excellent agreement of dHvA branches with LaRu4 Sb12 even in the smaller frequency branch (F B2 106 Oe) is clarified suggesting a well-localized character of 4f-electrons in PrRu4 Sb12 : A large difference of the FS topology between LaRu4 Sb12 and CeRu4 Sb12 is expected, which suggests the strong c–f hybridization or the itinerant nature of 4f-electrons in CeRu4 Sb12 : From the temperature dependence of the dHvA amplitude A; we can estimate the cyclotron effective
mass mnc as shown in Fig. 2. The mnc is found to be larger by more than two times than that of the LaRu4 Sb12 despite the smaller FS; mnc ¼ 1:1B1:7m0 for LaRu4 Sb12 [9]. The dHvA frequencies and cyclotron effective masses in CeRu4 Sb12 are listed in Table 1. Compared to the Sommerfeld coefficient of B100 mJ=K2 mol [5,6], the observed mnc is too small. If we simply estimate the Sommerfeld coefficient from the FS volume and mnc in the present experiments, the value should be B10 mJ=K2 mol: This disagreement can be naturally explained if there exists another FS (s) with a heavy mass of B50m0 ; that compensates the observed one. Under the present experimental conditions, the dHvA signal for such a heavy and small FS is hardly observable, that explains why only one dHvA branch has been observed in the present experiments. Taking into account the larger lattice constant in CeRu4 Sb12 compared to the semiconducting CeT4 X12 ; the small gap might lead to the heavy mass and the semimetallic FS. The authors are grateful to Prof. H. Harima for the helpful discussion. This work was supported by the Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.
266
H. Sugawara et al. / Physica B 312–313 (2002) 264–266
References [1] H. Sato, et al., Phys. Rev. 62 (2000) 15125, and references therein. [2] H. Sugawara, et al., J. Magn. Magn. Mater. 226–230 (2001) 48. [3] I. Shirotani, et al., J. Solid State Chem. 142 (1999) 146.
[4] D.T. Morelli, G.P. Meisner, J. Appl. Phys. 77 (1995) 3777. [5] N. Takeda, M. Ishikawa, Phys. B 259–261 (1999) 92; N. Takeda, M. Ishikawa, Phys. B 281–282 (2000) 388. [6] E.D. Bauer, et al., J. Phys.: Condens. Matter 13 (2001) 5183. [7] E.D. Bauer, et al., J. Phys.: Condens. Matter 13 (2001) 4495. [8] K. Abe, et al., unpublished (in preparation for this issue). [9] T.D. Matsuda, et al., Phys. B, this issue.