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Thermal expansion of CePt3Si under high pressure
ARTICLE IN PRESS
Physica B 378–380 (2006) 379–380 www.elsevier.com/locate/physb
Thermal expansion of CePt3 Si under high pressure Masashi Ohashia,, Gendo Oomia, Tomohito Nakanob, Yoshiya Uwatokoc a
Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan Department of Applied Physics, Waseda University, 3-4-1 Ohkubo Shinjuku-Ku, Tokyo 169-8555, Japan c ISSP University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581, Japan
b
Abstract We have carried out the thermal expansion measurement of CePt3 Si under pressure up to 3.0 GPa. It is found that a maximum in aðTÞ is observed and the temperature showing maximum T m increases significantly with increasing pressure having a coefficient qT m =qP ¼ 4 K=GPa. Assuming that T m corresponds to the Kondo temperature T K , qT K =qP is smaller than that of typical heavy fermion compounds such as CeCu6 . It comes from the fact that two kinds of interactions, the RKKY interaction and the Kondo effect, are competing each other. r 2006 Published by Elsevier B.V. PACS: 65.20.+w; 75.30.Mb; 74.62.Fj Keywords: Heavy fermion; Superconductivity; Antiferromagnetic order
CePt3 Si is a novel heavy fermion superconductor, crystallizing in the CePt3 B structure as a tetragonally distorted low symmetry variant of the AuCu3 structure type [1]. CePt3 Si exhibits antiferromagnetic order at T N ¼ 2:2 K and enters into a heavy fermion superconducting state at T C ¼ 0:75 K. Both transitions were observed clearly in the specific heat measurement. The normal state Sommerfeld value g was obtained to be 0:39 J=mol K2 . The Kondo temperature is estimated to be T K 11 K from susceptibility measurement [1]. It is well known that T K of heavy fermion compounds increases rapidly with increasing pressure to show a crossover into the intermediate valence state. In the present work, we made an attempt to measure the temperature dependence of thermal expansion of CePt3 Si at high pressure. The result is compared with that of typical heavy fermion compounds. Pollycristalline sample of CePt3 Si was prepared by melting constituent elements in an arc furnace. Thermal expansion Dl=l was measured by means of strain gage method [2], in which two gages were used as an active Corresponding author.
E-mail address: [email protected] (M. Ohashi). 0921-4526/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.physb.2006.01.134
(sample) and a dummy (reference) gage. Molybdenum (5N) was used as a reference material. Thermal expansion coefficient a was obtained by differentiating ðDl=lÞ with respect to T. Hydrostatic pressure up to 3.0 GPa was generated by using a piston–cylinder device which is made of Ni–Co–Cr–Mo (MP35N) alloy. DAFNE 7373 was used as a pressure transmitting medium. The detail of high pressure apparatus has been reported previously [3]. Fig. 1 shows aðTÞ below 50 K under high pressures up to 3 GPa. At 0.5 GPa, a shows a maximum around 13 K. T m and am are defined as the temperature and a showing the maximum in aðTÞ, respectively. This maximum is due to both Kondo and crystalline field as was seen in several Cebased compounds [4]. The Kondo temperature of the highest level, T hK is described as the relation, T hK ¼ ðD1 D2 T K Þ1=3 , where D1 and D2 are crystalline electric field excitation energies [5] and are estimated to be D1 12 K and D2 280 K [6] at ambient pressure. Assuming that D1 and D2 are independent to pressure, and T m corresponds to T K , T hK is estimated to be 35 K at 0.5 GPa, which is described by the open arrow in Fig. 1, and is roughly agreement with the temperature where aðTÞ has a shoulder. Such behavior is also observed in the magnetic contribution of electrical resistivity rmag ðTÞ, which is
ARTICLE IN PRESS 380
M. Ohashi et al. / Physica B 378–380 (2006) 379–380
Fig. 1. Thermal expansion coefficient aðTÞ at high pressures. Solid black arrows and an open arrow show the characteristic temperatures, T m and T hK , respectively (see the text).
characterized by a negative logarithmic term, followed by pronounced curvatures at about 15 KðT K Þ and 75 KðT hK Þ [1]. Both T m and am increase with increasing pressure. It is in agreement with a theoretical model for intermediate valence compounds [7] based on the periodic Anderson model. This model predicts the increase of am and T m when the 4f level approaches to the Fermi level. This evolution of a with pressure is similar to that for an intermediate valence compound CeNi0:8 Pt0:2 [8], in which an intermediate valence state is stabilized by applying pressure. In the case of CePt3 Si, on the other hand, it indicates a pressure induced crossover from low T K heavy fermion state to high T K intermediate valence state associated with the approach of 4f level to the Fermi level. Fig. 2 shows pressure dependence of T m for CePt3 Si. T m is found to increase with increasing pressure. The pressure derivative qT m =qP ¼ 4 K=GPa is an order of magnitude smaller than that of heavy fermion compounds: qT max =qP of CeCu6 is larger than 20 K/GPa [9], where T max is the temperature showing resistivity-maximum. It comes from the fact that T K is determined not only by the Kondo effect but also the RKKY interaction since CePt3 Si is an antiferromagnet at ambient pressure. Indeed, in the case of CeRh2 Si2 , which is an antiferromagnet at ambient pressure, the value of qT K =qP is related to the suppression of T N by applying pressure up to 1:0 GPað¼ PC Þ, that is, qT K =qP is 0.046 K/GPa below PC [10] while qT K =qP415 K=GPa is obtained above PC [11].
Fig. 2. Pressure dependence of T m of CePt3 Si.
In summary, the pressure dependence of Kondo temperature T K was obtained from the measurement of the thermal expansion of CePt3 Si. Since two kinds of interactions, the RKKY interaction and the Kondo effect, are competing each other, the pressure derivative qT K =qP is smaller than those of heavy fermion compounds without magnetic order.
References [1] E. Bauer, G. Hilscher, M. Michor, Ch. Paul, E.W. Scheidt, A. Gribanov, Yu. Seropegin, H. Noe¨l, M. Sigrist, P. Rogl, Phys. Rev. Lett. 92 (2004) 027003. [2] M. Ohashi, A. Tashiro, G. Oomi, A. Se nas, J. Rodrı´ guez Ferna´ndez, J.C. Go´mez Sal, Physica B 329–333 (2003) 1090. [3] F. Honda, S. Kaji, I. Minamitake, M. Ohashi, G. Oomi, T. Eto, T. Kagayama, J. Phys.: Condens. Matter 14 (2002) 11501. [4] G. Oomi, M. Ohashi, Y. Uwatoko, I. Satoh, T. Komatsubara, Physica B 359–361 (2005) 65. [5] F. Hanzawa, K. Yamada, K. Yoshida, J. Magn. Magn. Mater. 47&48 (1985) 357. [6] N. Metoki, K. Kaneko, T. Matsuda, A. Galatanu, T. Takeuchi, ¯ nuki, N. Bernhoeft, J. Phys.: S. Hashimoto, T. Ueda, R. Settai, Y. O Condens. Matter 16 (2004) L207. [7] G. Gangadhar Reddy, A. Ramakanth, Solid State Commun. 78 (1991) 113. [8] J. Rodrı´ guez Ferna´ndez, Y. Uwatoko, J.I. Espeso, J.C. Go´mez Sal, G. Oomi, Physica B 199&200 (1994) 506. [9] G. Oomi, T. Kagayama, H. Takahashi, N. Moˆri, T. Komatsubara, J. Alloys Compounds 192 (1993) 236. [10] H. Mori, N. Takeshita, N. Moˆri, Y. Uwatoko, Physica B 259–261 (1999) 58. [11] M. Ohashi, G. Oomi, S. Koiwai, M. Hedo, Y. Uwatoko, Phys. Rev. B 68 (2003) 114428.
Physica B 378–380 (2006) 379–380 www.elsevier.com/locate/physb
Thermal expansion of CePt3 Si under high pressure Masashi Ohashia,, Gendo Oomia, Tomohito Nakanob, Yoshiya Uwatokoc a
Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan Department of Applied Physics, Waseda University, 3-4-1 Ohkubo Shinjuku-Ku, Tokyo 169-8555, Japan c ISSP University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581, Japan
b
Abstract We have carried out the thermal expansion measurement of CePt3 Si under pressure up to 3.0 GPa. It is found that a maximum in aðTÞ is observed and the temperature showing maximum T m increases significantly with increasing pressure having a coefficient qT m =qP ¼ 4 K=GPa. Assuming that T m corresponds to the Kondo temperature T K , qT K =qP is smaller than that of typical heavy fermion compounds such as CeCu6 . It comes from the fact that two kinds of interactions, the RKKY interaction and the Kondo effect, are competing each other. r 2006 Published by Elsevier B.V. PACS: 65.20.+w; 75.30.Mb; 74.62.Fj Keywords: Heavy fermion; Superconductivity; Antiferromagnetic order
CePt3 Si is a novel heavy fermion superconductor, crystallizing in the CePt3 B structure as a tetragonally distorted low symmetry variant of the AuCu3 structure type [1]. CePt3 Si exhibits antiferromagnetic order at T N ¼ 2:2 K and enters into a heavy fermion superconducting state at T C ¼ 0:75 K. Both transitions were observed clearly in the specific heat measurement. The normal state Sommerfeld value g was obtained to be 0:39 J=mol K2 . The Kondo temperature is estimated to be T K 11 K from susceptibility measurement [1]. It is well known that T K of heavy fermion compounds increases rapidly with increasing pressure to show a crossover into the intermediate valence state. In the present work, we made an attempt to measure the temperature dependence of thermal expansion of CePt3 Si at high pressure. The result is compared with that of typical heavy fermion compounds. Pollycristalline sample of CePt3 Si was prepared by melting constituent elements in an arc furnace. Thermal expansion Dl=l was measured by means of strain gage method [2], in which two gages were used as an active Corresponding author.
E-mail address: [email protected] (M. Ohashi). 0921-4526/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.physb.2006.01.134
(sample) and a dummy (reference) gage. Molybdenum (5N) was used as a reference material. Thermal expansion coefficient a was obtained by differentiating ðDl=lÞ with respect to T. Hydrostatic pressure up to 3.0 GPa was generated by using a piston–cylinder device which is made of Ni–Co–Cr–Mo (MP35N) alloy. DAFNE 7373 was used as a pressure transmitting medium. The detail of high pressure apparatus has been reported previously [3]. Fig. 1 shows aðTÞ below 50 K under high pressures up to 3 GPa. At 0.5 GPa, a shows a maximum around 13 K. T m and am are defined as the temperature and a showing the maximum in aðTÞ, respectively. This maximum is due to both Kondo and crystalline field as was seen in several Cebased compounds [4]. The Kondo temperature of the highest level, T hK is described as the relation, T hK ¼ ðD1 D2 T K Þ1=3 , where D1 and D2 are crystalline electric field excitation energies [5] and are estimated to be D1 12 K and D2 280 K [6] at ambient pressure. Assuming that D1 and D2 are independent to pressure, and T m corresponds to T K , T hK is estimated to be 35 K at 0.5 GPa, which is described by the open arrow in Fig. 1, and is roughly agreement with the temperature where aðTÞ has a shoulder. Such behavior is also observed in the magnetic contribution of electrical resistivity rmag ðTÞ, which is
ARTICLE IN PRESS 380
M. Ohashi et al. / Physica B 378–380 (2006) 379–380
Fig. 1. Thermal expansion coefficient aðTÞ at high pressures. Solid black arrows and an open arrow show the characteristic temperatures, T m and T hK , respectively (see the text).
characterized by a negative logarithmic term, followed by pronounced curvatures at about 15 KðT K Þ and 75 KðT hK Þ [1]. Both T m and am increase with increasing pressure. It is in agreement with a theoretical model for intermediate valence compounds [7] based on the periodic Anderson model. This model predicts the increase of am and T m when the 4f level approaches to the Fermi level. This evolution of a with pressure is similar to that for an intermediate valence compound CeNi0:8 Pt0:2 [8], in which an intermediate valence state is stabilized by applying pressure. In the case of CePt3 Si, on the other hand, it indicates a pressure induced crossover from low T K heavy fermion state to high T K intermediate valence state associated with the approach of 4f level to the Fermi level. Fig. 2 shows pressure dependence of T m for CePt3 Si. T m is found to increase with increasing pressure. The pressure derivative qT m =qP ¼ 4 K=GPa is an order of magnitude smaller than that of heavy fermion compounds: qT max =qP of CeCu6 is larger than 20 K/GPa [9], where T max is the temperature showing resistivity-maximum. It comes from the fact that T K is determined not only by the Kondo effect but also the RKKY interaction since CePt3 Si is an antiferromagnet at ambient pressure. Indeed, in the case of CeRh2 Si2 , which is an antiferromagnet at ambient pressure, the value of qT K =qP is related to the suppression of T N by applying pressure up to 1:0 GPað¼ PC Þ, that is, qT K =qP is 0.046 K/GPa below PC [10] while qT K =qP415 K=GPa is obtained above PC [11].
Fig. 2. Pressure dependence of T m of CePt3 Si.
In summary, the pressure dependence of Kondo temperature T K was obtained from the measurement of the thermal expansion of CePt3 Si. Since two kinds of interactions, the RKKY interaction and the Kondo effect, are competing each other, the pressure derivative qT K =qP is smaller than those of heavy fermion compounds without magnetic order.
References [1] E. Bauer, G. Hilscher, M. Michor, Ch. Paul, E.W. Scheidt, A. Gribanov, Yu. Seropegin, H. Noe¨l, M. Sigrist, P. Rogl, Phys. Rev. Lett. 92 (2004) 027003. [2] M. Ohashi, A. Tashiro, G. Oomi, A. Se nas, J. Rodrı´ guez Ferna´ndez, J.C. Go´mez Sal, Physica B 329–333 (2003) 1090. [3] F. Honda, S. Kaji, I. Minamitake, M. Ohashi, G. Oomi, T. Eto, T. Kagayama, J. Phys.: Condens. Matter 14 (2002) 11501. [4] G. Oomi, M. Ohashi, Y. Uwatoko, I. Satoh, T. Komatsubara, Physica B 359–361 (2005) 65. [5] F. Hanzawa, K. Yamada, K. Yoshida, J. Magn. Magn. Mater. 47&48 (1985) 357. [6] N. Metoki, K. Kaneko, T. Matsuda, A. Galatanu, T. Takeuchi, ¯ nuki, N. Bernhoeft, J. Phys.: S. Hashimoto, T. Ueda, R. Settai, Y. O Condens. Matter 16 (2004) L207. [7] G. Gangadhar Reddy, A. Ramakanth, Solid State Commun. 78 (1991) 113. [8] J. Rodrı´ guez Ferna´ndez, Y. Uwatoko, J.I. Espeso, J.C. Go´mez Sal, G. Oomi, Physica B 199&200 (1994) 506. [9] G. Oomi, T. Kagayama, H. Takahashi, N. Moˆri, T. Komatsubara, J. Alloys Compounds 192 (1993) 236. [10] H. Mori, N. Takeshita, N. Moˆri, Y. Uwatoko, Physica B 259–261 (1999) 58. [11] M. Ohashi, G. Oomi, S. Koiwai, M. Hedo, Y. Uwatoko, Phys. Rev. B 68 (2003) 114428.